{"id":6051,"date":"2013-12-30T12:00:11","date_gmt":"2013-12-30T17:00:11","guid":{"rendered":"http:\/\/ezweather.com\/myblog\/?p=6051"},"modified":"2014-01-07T12:39:08","modified_gmt":"2014-01-07T17:39:08","slug":"donald-sutherland-winter-weather-column-december-updates","status":"publish","type":"post","link":"https:\/\/www.ezweather.com\/myblog\/2013\/12\/30\/donald-sutherland-winter-weather-column-december-updates\/","title":{"rendered":"Donald Sutherland – Winter Weather Column (December Updates)"},"content":{"rendered":"

Hi Everyone,<\/span><\/p>\n

Here’s Donald Sutherland’s Winter Weather Column for December. \u00a0As I kept updating his posts on this site for November, I’ll continue to do the same for this month.<\/span><\/p>\n

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In case you want to go back and read over his posts from November, click\u00a0here<\/a>.\u00a0<\/span><\/p>\n

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Posted Monday, December 30 @ 2:31 PM<\/abbr><\/strong><\/span><\/p>\n

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Afternoon thoughts…<\/span><\/p>\n

\u00a0<\/span><\/p>\n

For more than a week, the GFS and ECMWF ensembles have been indicating a period of severe cold for the first week of January (#388, #399) with only small timing differences on a run-to-run basis. As December comes to a close, the cold shot looks potentially even more impressive than first indicated. Below are the 12\/30 12z ECMWF, GFS, and MEX MOS numbers for lowest temperatures for select cities (1\/1-4\/2014):<\/span><\/p>\n

\u00a0<\/span><\/p>\n

\"12302013_2.jpg\"<\/p>\n

 <\/p>\n

At the same time, much above normal December snowfall in parts of the Mid-Atlantic region has often occurred in past winters that ultimately went on to have above average snowfall in parts of the Middle Atlantic and New England areas. The charts for cases in which Philadelphia, New York City, and Boston all received 8″ or more snowfall in December is below (NOTE: They were created on 12\/17 #359).<\/span><\/p>\n

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\"12172013_2.jpg\"<\/p>\n

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Posted Monday, December 30 @ 10:38 AM<\/abbr><\/strong><\/span><\/p>\n

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Not by Teleconnections Alone\u2026<\/span><\/p>\n

\u00a0<\/span><\/p>\n

For North America, the possibility of one or two bouts of severe to extreme cold to open the first 7-10 days of January appears increasingly likely. Whether or not the 12\/29 12z and 12\/30 0z ECMWF\u2019s idea of 1985- or 1994-style Arctic outbreaks verifies, the proverbial die has been cast that much of Canada, along with a large part of the eastern half of the CONUS will likely wind up colder than normal.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

With blocking developing\u2014the AO has now been negative for two consecutive days\u2014one should typically expect to see cold develop over parts of Europe where temperatures have been downright toasty. Indeed, Muscovites have sweated through a November that averaged almost 8\u00b0F above normal and December appears poised to finish at least as warm. Certainly, if one runs the maps for the forecast teleconnections, one sees a colder outcome.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

However, after a close look at the details beyond the teleconnections, the colder outcome appears unlikely. The persistent EPO- has led to an outcome in which almost all of the Northern Hemisphere\u2019s anomalous cold has drained into North America. The EPO- regime is likely to persist for the foreseeable future. As a result, very little anomalous cold will be available to be tapped for Europe despite what would typically be the development of a favorable synoptic pattern for cold.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Below are maps illustrating global cold anomalies for December 29, 2013; the December 1-28, 2013 timeframe for the Northern Hemisphere, and those for Decembers 1984 and 1993 for the Northern Hemisphere. Maps for the forecast teleconnection indices and January 1994 are also included.<\/span><\/p>\n

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\"12302013_1.jpg\"<\/p>\n

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December 1984 saw widespread cold anomalies in the Northern Hemisphere. December 1993, not unlike December 1-28, 2013 featured less expansive cold anomalies centered near North America. January 1985 wound up very cold across much of North America and also Europe. In contrast, North America experienced cold anomalies in January 1994, while much of Europe wound up warmer than normal.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

If one looks at the CFSv2\u2019s forecasts since 12\/20 (the beginning of its more skillful range), one finds a consistent theme of warmth in Europe. The GFS ensembles and ECMWF ensembles also indicate generally mild conditions through their extended range, with the GFS ensembles bringing about some cooling, particularly in southern Europe, Scandinavia, and extreme Western Europe at the end of their range. The 12\/30 0z run of the ECMWF produces anomalies very similar to the January 1994 map by 240 hours.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

In short, it appears that January 2013 could have warm anomalies centered near where they were centered in January 1994. The northern half of Scandinavia might wind up on the cool side of normal. Northern Africa and the Mideast might wind up near normal with perhaps some cool anomalies in the Mideast. But overall, one won\u2019t see the kind of widespread cold one saw in January 1985 despite what the teleconnection indices might imply.<\/span><\/p>\n

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Posted Sunday, December 29 @ 4:01 PM<\/abbr><\/strong><\/span><\/p>\n

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January 2014 Thoughts:<\/strong><\/span><\/p>\n

\u00a0<\/span><\/p>\n

There have been some winters where extremes in one or another teleconnection largely shaped the predominant pattern. For example, extreme blocking during winters 2009-10 and 2010-11 led to cold and snowy outcomes across parts of North America, in the former case during an El Ni\u00f1o and in latter with a La Ni\u00f1a. Since late autumn, it has been the negative to strongly negative EPO that has largely shaped the outcomes.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

My assumption has been that the EPO would be generally negative or neutral for the winter as a whole and I have little reason to see any radical shifts in the EPO\u2019s tendency for negative values to date through much of January. At the same time, a period of sustained blocking (AO) now appears likely for at least a part of January. In fact, it is plausible that the monthly average could be somewhat negative even if positive values return at some point.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

The outcome of such a combination would be cold across much of Canada and probably the eastern third to half of the CONUS. An exception would be Florida, parts of the Southeast, and the Gulf Coast, unless blocking is deeper or more sustained than what I assume will be the case.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Below are charts for the teleconnections as I see them for January (EPO: -1.75 to +0.25; AO -2.5 to +0.5; PNA: -0.5 to +0.3). I also produced a map using the teleconnections excluding the EPO just to illustrate the importance of the negative EPO this time around. The last chart is the latest CFSv2 forecast. The CFSv2 is now in the skillful range of its monthly forecasts.<\/span><\/p>\n

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\"January201412292013.jpg\"<\/p>\n

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Overall, I expect the following:<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Canada: Colder than normal, except northwestern Canada and parts of Atlantic Canada. The severe to extreme cold that will impact Quebec and New Brunswick should assure negative temperature anomalies there even if blocking eventually leads to some warming across northern Quebec, Labrador and Atlantic Canada.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Great Lakes, Northern Plains, Central Plains, Ohio Valley, New England, Mid-Atlantic region: Colder than normal, with the coldest anomalies probably centered from the Northern Plains, across the Upstate New York, and northern New England.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Southern Plains: Somewhat cooler than normal to near normal<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Southeast, Gulf Coast: Somewhat warmer than normal to warmer than normal.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Southwest and Pacific Northwest: Near normal to somewhat warmer than normal<\/span><\/p>\n

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Posted Sunday, December 29 @ 10:21 AM<\/abbr><\/strong><\/span><\/p>\n

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Morning thoughts…<\/span><\/p>\n

\u00a0<\/span><\/p>\n

1. A bout of\u00a0severe cold for the Great Lakes, Ohio Valley, Mid-Atlantic, New England, Ontario, and Quebec is now a high confidence idea. The ensembles have maintained the idea of a broad area of cold 1-2 standard deviations below normal with a small area of 3 standard deviations below normal during the first week of January.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

The idea of a subzero low in Boston and single-digit reading in New York City is a growing possibility. The last time that happened in both cities was January 24, 2011. Already, the GFS MOS shows a low of 12\u00b0 in NYC and 6\u00b0 in Boston. It also shows low temperatures of -4\u00b0 in Albany, -9\u00b0 in Burlington, 12\u00b0 in Columbus, 7\u00b0 in Detroit, -27\u00b0C (-17\u00b0F) in Montreal, 14\u00b0 in Philadelphia,\u00a0and -19\u00b0C (-2\u00b0F) in Toronto.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

2. Ahead of the Arctic front a Miller B-type system will likely form somewhere off the Mid-Atlantic Coast with a primary system moving into the Ohio Valley. Climatology and the ECMWF, which with its higher resolution should have a better idea of what is a complex set of variables in a fast flow, both favor a higher impact on some portion of New England than the Mid-Atlantic. There remains a lot of uncertainty, but at least some accumulations appear possible from Philadelphia to New England.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

3. Some guidance features a second shot of cold, perhaps behind another period of snow,\u00a0toward the end of the first week in January.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

4. In the longer-range, the coldest anomalies could shift westward some time after the first week in January for a time.<\/span><\/p>\n

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Posted Saturday, December 28 @ 9:03 AM<\/abbr><\/strong><\/span><\/p>\n

\n

January 8-15, 2014 Thoughts<\/strong><\/span><\/p>\n

\u00a0<\/span><\/p>\n

After a cold first week of January, highlighted by a bout of severe cold, along with at least some accumulating snow across parts of the eastern CONUS, the pattern appears poised to see the cold anomalies shift westward. There had been some question about the PNA, with the GFS ensembles having reverted back to a primarily negative PNA after having forecast a positive PNA for several runs. Overnight, the ECMWF ensembles yielded and they now forecast a PNA- developing by 240 hours. Both sets of ensembles shift the coldest anomalies westward, as well. Nevertheless, the ensembles have maintained good run-to-run continuity on the idea of an EPO-\/AO-. This could become important beyond mid-month.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Below are charts showing cold\/warm anomalies based on the forecast teleconnections and the NAEFS. A positive PNA would have led to the cold’s being centered farther east.<\/span><\/p>\n

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\"Jan8_152014.jpg\"<\/p>\n

 <\/p>\n

What’s interesting among the teleconnection dates is that January 13-16, 1994 and January 11-15, 2013 are among them. In both cases, the cold again came eastward, so that will be something to watch for. If so, the period of moderation could be temporary. More data will be required, but what appears likely is that moderation won’t mean that winter is finished even if the milder temperatures might tempt one in that direction.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

In terms of outcomes, I expect the Northern and Central Plains, along with much of Canada to turn out colder than normal. The Mid-Atlantic, Southeast and Gulf Coast should be warmer than normal. The Southwest could also be near normal to somewhat warmer than normal. New England and the Pacific Northwest will probably be near normal.<\/span><\/p>\n

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Posted Friday, December 27 @ 2:54 PM<\/abbr><\/strong><\/span><\/p>\n

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More on the Upcoming Cold Start for January…<\/span><\/p>\n

\u00a0<\/span><\/p>\n

This message builds on the data from Message #388.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

First, the 12\/27 12z GFS ensembles and 12\/27 12z ECMWF are in good agreement that a potentially severe shot of cold will impact the Great Lakes region to the Middle Atlantic and New England areas during the 1\/1-3 period. The 12\/27 12z run of the GFS delays the cold shot for several days beyond either the GFS ensembles or ECWMF. Hence, I cautiously favor the GFS ensemble-ECMWF combination for the timing of the cold.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Second, the latest run of the GFS ensembles now shows an area of cold anomalies in a narrow portion of Quebec that is 3 or more standard deviations below normal. Below are charts for the operational GFS and temperatures for select cities relative to the standardized anomalies (this table supplements the table for a number of additional cities that was posted in Message #388.<\/span><\/p>\n

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\"12272013_2.jpg\"<\/p>\n

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In addition, below are the lowest temperatures forecast by the 12z run of the ECMWF for all the cities in both tables:<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Albany: -25.4\u00b0C (-14\u00b0F)<\/span><\/p>\n

Boston: -24.1\u00b0C (-11\u00b0F)<\/span><\/p>\n

Burlington: -33.3\u00b0C (-28\u00b0F)<\/span><\/p>\n

Columbus: -13.8\u00b0C (7\u00b0F)<\/span><\/p>\n

Detroit: -16.3\u00b0C (3\u00b0F)<\/span><\/p>\n

Montreal: -37.0\u00b0C (-35\u00b0F)<\/span><\/p>\n

New York City: -13.0\u00b0C (9\u00b0F)<\/span><\/p>\n

Philadelphia: -12.1\u00b0C (10\u00b0F)<\/span><\/p>\n

Toronto: -24.4\u00b0C (-12\u00b0F)<\/span><\/p>\n

Washington, DC: -11.0\u00b0C (12\u00b0F)<\/span><\/p>\n

\u00a0<\/span><\/p>\n

For perspective, the Montreal temperature would be an amazing 3.54 standard deviations below normal, if it verified. New York City would have its first single-digit low since January 24, 2011 when the mercury fell to 6\u00b0. Boston would have its first subzero low since January 24, 2011 when the temperature reached -2\u00b0. The last time Boston had a temperature of -10\u00b0 or lower was January 15, 1957 when the temperature bottomed out at -12\u00b0.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

In sum, while it remains to be seen whether the ECMWF is overdone with some of the temperatures, the agreement between the GFS ensembles and ECMWF provide some degree of confidence that a potentially severe shot of cold lies ahead and that it could produce the colder readings in some major cities than one has witnessed during the most recent winters.<\/span><\/p>\n

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Posted Friday, December 27 @ 8:30 AM<\/abbr><\/strong><\/span><\/p>\n

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Some morning thoughts…<\/span><\/p>\n

\u00a0<\/span><\/p>\n

1. The GFS ensembles have returned to showing the redevelopment of a PNA- pattern by around 240 hours. Such a pattern would lead to ridging in the East and cold shifting farther west. Subsequent GFS ensemble forecasts show a trough in the West\/ridge in the East configuration.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

2. The reforecast ensembles show a similar development.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

3. The ECMWF ensembles are not as keen on that idea through 240 hours. Neither are the objective analogs based on the GFS ensembles.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

No matter the outcome, a large part of the eastern CONUs except Florida and perhaps a portion of the Gulf Coast and Southeast will wind up colder than normal, on average, for the first week of January with the Great Lakes Region, Ohio Valley, northern Mid-Atlantic, New England, Ontario, and Quebec seeing perhaps a brief bout of severe cold. The GFS ensembles show a small portion of Quebec having temperatures 3 standard deviations below normal on 1\/1 and a large part of the East having readings at least 1 standard deviation below normal.<\/span><\/p>\n

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Posted Wednesday, December 25 @ 3:28 PM<\/abbr><\/strong><\/span><\/p>\n

Some afternoon thoughts…<\/span><\/p>\n

\u00a0<\/span><\/p>\n

I hope that all who celebrate Christmas will find a KU snowstorm for sometime this season among the gifts under the Christmas Tree. For some, the snow squalls that briefly brought low visibilities and blanketed the ground in white, also brought renewed hope for the winter as a whole. Certainly, a number of cities in the northern Mid-Atlantic region(unfortunately, not the long-suffering Washington area)\u00a0have enjoyed above normal snowfall to date and such snowfall in December has often been a precursor of a snowy winter.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

The\u00a0guidance continues to show a generally cold start for the first week of 2014 across a large part of the CONUS and Canada. How the Arctic Oscillation (AO) evolves could play a large role in determining whether the first week cold is an appetizer for a main course of snow and cold.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Currently, the GFS ensembles have two ideas. The first hints a potential period of blocking. The second shows just a brief period, at best, with the persistent AO+ regime generally holding. The former could lead to a cold January in much of Canada and the eastern half of the CONUS. The second could see a finger of cold anomalies centered farther west, perhaps somewhere in the vicinity of the Plains States and Great Lakes region. Under that scenario, storms could more readily cut for the Great Lakes. Canada would be generally cold under both scenarios. The former would also have the potential to produce more widespread cold in Europe.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Given the remarkable persistence of the AO+, it makes sense to hedge somewhat away from the first scenario until more data for that idea becomes available. After all, as one approached December, one saw a “false alarm” for an appreciable period of blocking for December. That idea never verified.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

In any case, no matter the scenario that plays out, it appears unlikely that January would see almost unrelenting warmth on a\u00a0coast-to-coast basis. Absent that scenario, opportunities for winter weather should be available at least from time to time.<\/span><\/p>\n

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Posted Monday, December 23 @ 11:40 AM<\/abbr><\/strong><\/span><\/p>\n

Ensembles: EPO-, AO-, PNA+ Combination Growing More Likely…<\/span><\/p>\n

\u00a0<\/span><\/p>\n

The ensemble data has maintained continuity with the idea that the AO will go negative and the PNA+, while the EPO remains generally negative, near or during the first week in January. Such a combination has, in the means, seen cold anomalies in a large part of eastern North America.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Consistent with that outcome, the GFS ensembles are currently showing cold anomalies of 1\u03c3\u00a0– 2\u03c3\u00a0below normal for\u00a0the start of January. Below are the maps for 1\/1 and 1\/2, along with high and low temperatures associated with a\u00a0standardized anomalies ranging from 1\u03c3\u00a0to 3\u03c3\u00a0below normal for select cities (1\/1-3\u00a0for the 1981-2010 base period) for select cities.\u00a0<\/span><\/p>\n

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\"12232013_3.jpg\"<\/p>\n

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Although this outcome is not yet cast in proverbial stone, odds favor the first week of January averaging colder than normal in the eastern half of North America. Also, the timing of the cold shot could shift a little making the 12\/30\/2013-1\/3\/2014 period perhaps the most likely timeframe. The possibility of the kind of strong cold shot shown on the GFS ensembles is a realistic one if the AO- and PNA+ develop as currently modeled.<\/span><\/p>\n

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************************************************************************************************************************************************Posted Monday, December 23 @ 10:01 AM<\/abbr><\/strong><\/span><\/p>\n

A final note on the 12\/22\/2013 record high minimum temperatures…<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Below is a chart showing the records for select cities and standardized anomalies relative to the normal 12\/22 low temperature:<\/span><\/p>\n

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\"12232013_2.jpg\"<\/p>\n

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************************************************************************************************************************************************Posted Monday, December 23 @ 8<\/span>:14 AM<\/span>
\n<\/abbr><\/strong><\/p>\n

\u00a0<\/abbr><\/strong><\/p>\n

Record-tying and record-breaking high minimum temperatures for select cities for December 22, 2013:<\/span><\/p>\n

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\"12232013_1.jpg\"<\/p>\n

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NOTE: The December record high minimum temperature for IAD is 61\u00b0, which was set on December 23, 1990.<\/span><\/p>\n

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************************************************************************************************************************************************Posted Sunday, December 22 @ 11<\/span>:11 PM<\/span>
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Record-tying and record-breaking high temperatures from select cities for December 22, 2013:<\/span><\/p>\n

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\"Record_Highs12222013.jpg\"<\/p>\n

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************************************************************************************************************************************************Posted Sunday, December 22 @ 9:43 AM<\/abbr><\/strong><\/span><\/p>\n

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January 1-7, 2014 Thoughts:<\/strong><\/span><\/p>\n

Already, this morning record high temperatures had fallen in many cities in the eastern U.S. Cities included Atlanta, Baltimore, New York, Newark, and Philadelphia. Temperatures in that part of\u00a0North America were running in the 60s and even 70s. However, if one looks ahead to the first week of January, a return of more winterlike conditions appears increasingly likely.\u00a0<\/span><\/p>\n

\u00a0<\/span><\/p>\n

The ensemble guidance have been suggesting a change in both the AO and PNA heading into the first week in January. Today’s run shows the most decided signal yet for an AO- and PNA+ pattern. The EPO is forecast to remain predominantly negative. Nevertheless, given the PDO- and persistent AO+, some consideration has to be given to a more modest change in the indices.<\/span><\/p>\n

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\"January1_72014.jpg\"<\/p>\n

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The outcomes based on the forecast teleconnections and those shown on the GFS ensembles for 1\/5\/2014 0z are quite similar. As a result, my guess is that much of Canada, except for the extreme north and western portions will likely wind up colder than normal. A cold January looks increasingly likely across much of Canada, as well. Much of the CONUS will also wind up colder than normal with perhaps the coldest anomalies located somewhere near the Great Lakes region. Exceptions will be the western quarter of the U.S., particularly the Southwest and Pacific Northwest where warmer conditions appear likely. The Southeast and Gulf Coast may wind up close to normal with some warmer than normal anomalies, particularly across Florida where winter has been largely absent so far.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

As an added bonus, the ensembles have consistently signaled the possibility of a storm that could develop somewhere in the Gulf region and then move off the coast of the Southeastern U.S.\/lower Mid-Atlantic. Storm tracks are low skill at this time, but the important point is that the cold might coincide with some storminess in parts of the eastern CONUS.<\/span><\/p>\n

************************************************************************************************************************************************Posted Saturday, December 21 @ 1:44 PM<\/abbr><\/strong><\/span><\/p>\n

Record Warmth Now Underway…\u00a0<\/span><\/p>\n

Already, Atlantic City, Baltimore, Charleston, SC, Norfolk, Savannah, Washington, DC, and Wilmington, DE have broken daily record high temperatures. At Savannah, the temperature had reached 81\u00b0 as of 1 pm. That was the 5th time this month Savannah has had a temperature of 80\u00b0 or above. Only 1931 with 6 such dates has had more.<\/span><\/p>\n

************************************************************************************************************************************************Posted Thursday, December 19 @ 12:00 PM<\/abbr><\/strong><\/span><\/p>\n

\u00a0<\/abbr><\/strong><\/p>\n

The big weather story in the near-term will be the potential bout of record warmth in parts of the East that could occur ahead of an approaching cold front on Sunday, December 22. The GFS ensembles indicate a large area of readings 1.5\u03c3 to 2.5\u03c3 above normal for December 23 0z.<\/span><\/p>\n

 <\/p>\n

\"12192013_1.jpg\"<\/p>\n

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That would translate into readings into at least the 60s in the northern Mid-Atlantic and possibly some areas reaching or exceeding 70\u00b0.<\/span><\/p>\n

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\"12192013_2.jpg\"<\/p>\n

 <\/p>\n

For the longer range, there are some hints that a period where the EPO goes neutral or even slightly positive (recent ensemble runs) may yield to a renewed EPO- regime.As a result, while it is too early to have much confidence in the overall North American temperature anomalies for January, odds are increasing that at least a large portion of Canada could be colder than normal. That would be in marked contrast to the recent runs of the CFSv2 that have been depicting a classic EPO+\/WPO+ pattern.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Finally, the AO+ regime still looks to hold through the ensemble range. Through today, the AO has been positive on 86% of days during the November 1-December 19 period. During November-December 2006, the AO was positive on 90% of days and during the same timeframe in 2011, it was positive on 95% of days. If winters 2006-07 and 2011-12 (the only case where the AO averaged +1 or above for both November and December) have some relevance, a period of blocking could develop at some point in January, probably during the second half of the month. Both winter 2006-07 and winter 2011-12 saw a period of blocking develop on January 21. For winter 2006-07, the blocking lasted just 6 days, but marked the start of a dramatic pattern change that saw blocking redevelop and persist through almost all of February. In winter 2011-12, the period of blocking lasted 22 days and a persistent AO+ regime returned afterward. Given both the Snow Advance Index (SAI) and October Pattern Index (OPI), odds probably favor a resumption of the AO+ regime should blocking develop later in January. Needless to say, one can\u2019t be confident in the development of a period of blocking in January, but recent persistent November-December AO+ regimes have led to such an outcome. Those AO+ regimes include 1994-95 (period of blocking developed 1\/19) and 1999-00 (blocking developed 1\/17).<\/span><\/p>\n

************************************************************************************************************************************************Posted Tuesday, December 17 @ 1:56 PM<\/abbr><\/strong><\/span><\/p>\n

December snowfall in parts of the Middle Altantic and New England regions has been similar to what has occurred in winters that proved snowy, particularly in Philadelphia and New York City. Through December 16, monthly snowfall was as follows:<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Boston: 5.0″<\/span><\/p>\n

New York City: 7.1″<\/span><\/p>\n

Philadelphia: 11.1″<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Following today’s clipper system, both Boston and New York City will likely have reached or exceeded 8″ of snow for December. Going back to 1888, there were 12 years during which December snowfall reached 8″ or more in Boston, New York City, and Philadelphia. Those years and seasonal snowfall for Boston, New York City, Philadelphia, and Washington, DC are listed below. It should be noted that monthly snowfall in Washington, DC is currently lower than it was for all 12 cases, so that\u00a0creates greater uncertainty aside from the relatively small sample that is involved.<\/span><\/p>\n

 <\/p>\n

\"12172013_2.jpg\"<\/p>\n

************************************************************************************************************************************************Posted Monday, December 16 @ 8:25 AM<\/abbr><\/strong><\/span><\/p>\n


\n<\/abbr><\/strong><\/p>\n

Quick morning thoughts…<\/span><\/p>\n

\u00a0<\/span><\/p>\n

The EPO has now been negative for 39 consecutive days. The most prolonged negative EPO regime that commenced in November was 45 days (2010). The latest ensembles show the EPO going weakly positive around or just after 12\/22, but perhaps only temporarily.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

The AO is now above +4.000 for the second consecutive day. The AO will very likely remain positive for at least the next 1-2 weeks.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

The near-term excitement will concern a clipper system (possibly with a second weaker disturbance on its heels) that should bring a fairly wide 1″-3″ snowfall across parts of the northern Mid-Atlantic region and across a large swatch of southern and central New England. This system appears to be more robust than most clipper systems, so it could tap Atlantic moisture producing some areas of 3″-6″ snowfall. Where those enhanced areas of snowfall set up are difficult to pin down. Trying to do so is a lot like trying to pinpoint where thunderstorms will pop up on a humid summer day. Nevertheless, a portion of southern New England might have the highest chance of seeing such enhanced snowfall.<\/span><\/p>\n

 <\/p>\n

 <\/p>\n

************************************************************************************************************************************************Posted Sunday, December 15 @ 9:22 PM<\/abbr><\/strong><\/span><\/p>\n


\n<\/abbr><\/strong><\/p>\n

Mid-Month Update:<\/strong><\/span><\/p>\n

\u00a0<\/span><\/p>\n

To date, the month has been characterized by an EPO-\/AO+ pattern. Today, the AO was +4.201. That breaks the daily record high of +3.159, which was set in 2006. Nevertheless, unlike 2006, a snowstorm brought more than a foot of snow across parts of Maine. In 2006, the EPO was +1.589. Today, it was approximately -1.3.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Nevertheless, the ensembles have been hinting that the EPO could become more neutral as December winds down.<\/span><\/p>\n

 <\/p>\n

\"12152013_1.jpg\"<\/p>\n

 <\/p>\n

To date, the predominant EPO\/AO pattern has produced outcomes fairly close to those shown for the partial teleconnection cases (excluding ENSO) for the month of December (Message #204 of 11\/30). If, however, the more neutral EPO materializes, one could see the cold anomalies lift into Canada, and milder anomalies prevail, on average, during January. The 360-hour reforecast ensembles hint at a possible pattern evolution toward a milder January outcome. Fortunately, at this point in time, the skill level of both is low.<\/span><\/p>\n

 <\/p>\n

\"12152013_2.jpg\"<\/p>\n

 <\/p>\n

Finally, the snowfall that has blanked parts of the northern Mid-Atlantic this month, including the snowfall that appears likely on Tuesday courtesy of two clipper systems racing eastward, is providing a hint that the northern Mid-Atlantic region into southern New England may experience normal to above normal snowfall for the winter. For example, Philadelphia has already received 11.1″ snow this month. 8\/9 (89%) of winters that received 10″ or more snowfall in December since 1872\u00a0wound up with 20″ or more seasonal snowfall. and 6\/9 (67%) had 30″ or more.\u00a0The sample size is small, but the probability is very high, so odds probably lean toward a winter with 20″ or more snowfall.<\/span><\/p>\n

\u00a0<\/abbr><\/strong><\/p>\n

************************************************************************************************************************************************Posted Friday, December 13 @ 11:25 PM<\/abbr><\/strong><\/span><\/p>\n

December 23-31, 2013 Thoughts:<\/strong><\/span><\/p>\n

\u00a0<\/span><\/p>\n

In terms of teleconnections, the ensembles continue to favor a predominant EPO-, AO+, PNA+ regime during the closing days of December. At the same time, a large area of cold continues to cover North America and there is little evidence that the cold will be driven from North America anytime soon. Consequently, areas adjacent to the cold will likely wind up colder than normal, as well, even if 500 mb pattern might be expected to have some warmth into those areas.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Below are a number of charts showing the temperature anomalies associated with the forecast ENSO-teleconnections, teleconnections alone, GFS ensembles, and NAEFS.<\/span><\/p>\n

 <\/p>\n

\"Dec23to312013.jpg\"<\/p>\n

 <\/p>\n

Continuity with the predominant pattern since November argues that the areas of warmth could be more limited than depicted on some of the above charts. There also remains a distinct possibility of an Arctic outbreak sometime during the 12\/23-31 period with perhaps the coldest anomalies focused on the Plains States into central Canada.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

In terms of overall anomalies for the 12\/23-31 period, my thoughts are as follows:<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Much of Canada: Colder than normal<\/span><\/p>\n

Northern and Central Plains: Colder than normal<\/span><\/p>\n

Great Lakes Region\/Ohio Valley: Colder than normal<\/span><\/p>\n

Pacific Northwest: Near normal<\/span><\/p>\n

New England and the Middle Atlantic Region: Colder than normal<\/span><\/p>\n

Southeast\/Gulf States: Warmer than normal<\/span><\/p>\n

Southern Plains (including Texas): Somewhat cooler than normal to near normal<\/span><\/p>\n

Desert Southwest: Warmer than normal<\/span><\/p>\n

************************************************************************************************************************Posted Thursday, December 12 @ 11:32 AM<\/abbr><\/strong><\/span><\/p>\n

 <\/p>\n

Some morning thoughts…<\/span><\/p>\n

\u00a0<\/span><\/p>\n

The EPO and AO remain remarkably stable at their respective negative and positive states. The ensemble guidance shows little meaningful change from those states, even as their values are forecast to change. However, if one is looking for a possible evolution that could have longer-term implications, the ensemble guidance has slowly been shifting from persistent PNA- values to neutral values. Some ensemble members even point to the development of a weakly positive PNA.<\/span><\/p>\n

 <\/p>\n

\"12122013_1.jpg\"<\/p>\n

 <\/p>\n

If the PNA does, in fact, evolve as currently shown on the ensembles, the stage could be set for widespread cold anomalies in North America for the closing week of December. Moreover, a number of winters that saw such an evolution wound up with a cold January in Canada and parts of the northern CONUS. Hence, the potential evolution might have implications beyond the close of December.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

For now, those are ensemble forecasts. But at least one possible evolution would lead to cold and possible opportunities for snowfall, especially if ENSO Region 3.4 (current anomaly of +0.2\u00b0C experiences additional warming as the winter progresses).<\/span><\/p>\n

************************************************************************************************************************************************Posted Saturday, December 7 @ 11:09 AM<\/abbr><\/strong><\/span><\/p>\n

At Jordan, MT, the temperature fell to at least -42\u00b0 this morning. That shattered the daily record of -37\u00b0, which was set in 1927. Today’s frigid temperature was that city’s first -40\u00b0 temperature since January 12, 1998 when the temperature also fell to -40\u00b0. It\u00a0was also that city’s first December temperature of -40\u00b0 or below since December 31, 1992 when the temperature reached -40\u00b0. It was the coldest reading since December 22, 1989 when the thermometer fell to -45\u00b0. Finally, it was the earliest -40\u00b0 temperature on record beating the previous early date of December 21, 1989.<\/span><\/p>\n

**************************************************************************************************************************************************************<\/p>\n

Posted Saturday, December 7 @ 8:36 AM<\/abbr><\/strong><\/span><\/p>\n

This morning’s low temperature at Havre, MT has so far been -39\u00b0. That reading is its\u00a0third consecutive daily record low temperature and its coldest reading during the 2000-present period.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Its readings for the past two days have been:<\/span><\/p>\n

\u00a0<\/span><\/p>\n

12\/5 High: -14\u00b0 (broke daily record of -12\u00b0, 1880); Low: -28\u00b0 (broke daily record of -27\u00b0, 1956)<\/span><\/p>\n

12\/6 High: -13\u00b0; Low: -38\u00b0 (broke daily record of -31\u00b0, 1972<\/span><\/p>\n

\u00a0<\/span><\/p>\n

The 12\/5 high was also the lowest high temperature during the 2000-present period<\/span><\/p>\n

************************************************************************************************************************************************Posted Friday, December 6 @ 11:40 PM<\/abbr><\/strong><\/span><\/p>\n

Today, Portland, OR had a high temperature of 30\u00b0. That was Portland’s first subfreezing day since November 23, 2010 when the temperature also topped out at 30\u00b0. It was also the 2nd lowest daily maximum reading on record, tied with 1956. The record is 27\u00b0, which was set in 1972.\u00a0<\/span><\/p>\n

In addition, Portland picked up 0.5″ snow. That was the second largest snowfall for this date, tied with 1994. The daily record is 2.0″, which was set back in 1942.<\/span><\/p>\n

************************************************************************************************************************************************Posted Friday, December 6 @ 11:09 PM<\/abbr><\/strong><\/span><\/p>\n

 <\/p>\n

December 16-22, 2013 Thoughts:<\/strong>\u00a0<\/span><\/p>\n

Historical experience argues for the EPO to go neutral or positive within a week after mid-month, but the ensembles show a rise but do not conclusively agree on that outcome. As a consequence, my thoughts assume an EPO that is a compromise (neutral to somewhat negative through the duration of the period in question.<\/span>
\n\u00a0<\/span><\/p>\n

There are also some differences between the GFS ensembles and the reforecast ensembles. Considering the existence of somewhat of a disconnect between the objective analogs based on the GFS ensembles and the outcome for the ensembles themselves, as well as the reforecast ensembles showing more cold air in Canada, I suspect that the reforecast ensembles probably are closer to reality. The ensembles may be reducing the expanse of cold anomalies in Canada a little more quickly.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Nevertheless, the outcome suggests milder conditions will likely become more widespread across the CONUS during the period, though parts of the northern tier could still wind up colder than normal. A cold shot, particularly early in the period could impact the East.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Below are charts showing the ENSO+teleconnection cases, teleconnection cases excluding ENSO, the reforecast ensembles, and most recent run of the NAEFS:<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Overall, my thoughts err on the colder side across parts of the Northern tier of the CONUS for the overall anomalies during the period. Specifically, my thoughts are as follows:<\/span><\/p>\n

 <\/p>\n

\"Dec16to222013.jpg\"<\/p>\n

 <\/p>\n

Canada: Almost all of Canada would wind up with cold anomalies for the period as a whole.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Pacific Northwest, Northern Plains, Great Lakes region, New England: Somewhat cooler than normal.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Southwest, Central\/Southern Plains, Mid-Atlantic: Generally warmer than normal, but the northern Mid-Atlantic could wind up near to normal.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Southeast\/Gulf Coast: Warmer to possibly much warmer than normal.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

************************************************************************************************************************************************Posted Thursday, December 5 @ 9:58 AM
\n<\/abbr><\/strong><\/span><\/p>\n

The ensemble data continues to show a retrograding ridge that could lead to the EPO’s going neutral and then possibly positive after mid-month. In response, a milder pattern could set in across at least parts of the CONUS. Moreover, it appears that the possible pattern change could be hemispheric in nature.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

For example, both the ensembles and also partial teleconnection cases indicate a much warmer regime could set in across northern Europe where coming days will very likely produce readings 1-2 standard deviations below normal.<\/span><\/p>\n

 <\/p>\n

\"12052013.jpg\"<\/p>\n

 <\/p>\n

While nothing is cast in stone yet, there continue to enough signals to watch for a possible pattern change down the road. For now one of the most extreme early-season Arctic air masses in North America in recent years\u00a0is making weather headlines.<\/span><\/p>\n

**************************************************************************************************************************************************************Posted Thursday, December 5 @ 8:27 AM<\/abbr><\/strong><\/span><\/p>\n

A further note on Denver, which has so far had a reading of -15\u00b0 today, tying the daily mark set in 1972:<\/span><\/p>\n

\u00a0<\/span><\/p>\n

In terms of days on which the temperature fell to -10\u00b0 or lower prior to December 5, the only prior days were during the 19th century. Those dates, including yesterday’s reading are:<\/span><\/p>\n

\u00a0<\/span><\/p>\n

11\/28\/1877 -10\u00b0<\/span><\/p>\n

11\/29\/1877 -18\u00b0<\/span><\/p>\n

11\/30\/1877 -10\u00b0<\/span><\/p>\n

\u00a0<\/span><\/p>\n

11\/17\/1880 -14\u00b0<\/span><\/p>\n

11\/18\/1880 -12\u00b0<\/span><\/p>\n

11\/29\/1880 -10\u00b0<\/span><\/p>\n

\u00a0<\/span><\/p>\n

11\/27\/1887 -14\u00b0<\/span><\/p>\n

\u00a0<\/span><\/p>\n

12\/4\/2013 -13\u00b0<\/span><\/p>\n

************************************************************************************************************************************************Posted Thursday, December 5 @ 8:07 AM<\/abbr><\/strong><\/span><\/p>\n

On the warm side, Atlanta has had a low temperature of 65\u00b0 so far today. The daily record high minimum temperature is 60\u00b0, which was set in 1998. If today’s figure holds, that would be the second warmest minimum temperature on record for Atlanta in December, tied with 65\u00b0 on 12\/1\/1991 and just behind 68\u00b0 on 12\/2\/1991.<\/span><\/p>\n

************************************************************************************************************************************************Posted Wednesday, December 4 @ 5:46 PM<\/abbr><\/strong><\/span><\/p>\n

 <\/p>\n

Growing Hints of an EPO Flip…<\/strong><\/span><\/p>\n

\u00a0<\/span><\/p>\n

As had been noted previously (#197), historical experience argued that one should watch for the EPO’s possibly shifting to positive by mid-December +\/- 1 week. The longest stretch during which the EPO had remained negative after such a regime commenced in November was 45 days. The second and third longest such streaks were 33 and 32 days respectively.Through today, the EPO has been negative for 26 consecutive days.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

The latest guidance is now showing the EPO rising toward 0 in the extended range. Some individual ensemble members take it positive.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Below is the latest reforecast ensemble mean forecast from CDC:<\/span><\/p>\n

 <\/p>\n

\"EPO12042013.jpg\"<\/p>\n

 <\/p>\n

Such an outcome, particularly if the AO remains positive, would have potential implications. It would tend to favor milder weather across at least parts of the CONUS and, depending on the overall pattern evolution, possibly on a widespread basis. The composite EPO\/AO combinations for the December 16-31 period are below:<\/span><\/p>\n

 <\/p>\n

\"EPOAO1216to3119812010.jpg\"<\/p>\n

**************************************************************************************************************************************************************Posted Wednesday, December 4 @ 9:20 AM<\/abbr><\/strong><\/span><\/p>\n

Morning thoughts…<\/span><\/p>\n

\u00a0<\/span><\/p>\n

1. The well-modeled cold has now moved into the Pacific Northwest and Northern Plains<\/span><\/p>\n

\u00a0<\/span><\/p>\n

2. In the extended range, the AO and PNA look to remain locked in what has been their predominant state through the late fall into early winter: AO+ and PNA-. The ensemble guidance continues to indicate a relaxation of the EPO-.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

3. Consistent with the forecast teleconnections, there are growing indications on the ensembles of a milder pattern in the long-range after mid-month (~12\/20 +\/- a few days might be reasonable timing)\u00a0for the CONUS while Canada remains cold for the most part. This progression is also consistent with the evolution of the composite pattern associated with predominant EPO-\/AO+ regimes (1950-2012).<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Given how far out that possible change is, it is still within the speculative realm. Nevertheless, it is perhaps something to watch for in subsequent guidance, especially as it is consistent with the evolution of past EPO-\/AO+ regimes. It is also not dissimilar to the evolution of the late November\/December 2008 pattern that has\u00a0provided\u00a0insight in recent weeks. 2008 also continues to show\u00a0up among the GFS ensemble analogs (Day 8 and Day 11). \u00a0<\/span><\/p>\n

************************************************************************************************************************************************Posted Tuesday, December 3 @ 5:13 PM<\/abbr><\/strong><\/span><\/p>\n

 <\/p>\n

To put the coming cold for parts of the Northern Plains into perspective, the MEX MOS shows the following lowest maximum and lowest minimum temperatures for Havre, MT\u00a0and Jordan, MT:<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Havre:<\/span><\/p>\n

Lowest Maximum: -17\u00b0<\/span><\/p>\n

Lowest Minimum: -37\u00b0<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Jordan:<\/span><\/p>\n

Lowest Maximum: -17\u00b0<\/span><\/p>\n

Lowest Minimum: -40\u00b0<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Below is a chart showing the lowest December maximum and minimum temperatures beginning in 2000:<\/span><\/p>\n

 <\/p>\n

\"MT2013.jpg\"<\/p>\n

************************************************************************************************************************************************<\/p>\n

Posted Tuesday, December 3 @ 1:10 PM<\/abbr><\/strong><\/span><\/p>\n


\nWith regard to the unfolding cold in the Pacific Northwest and Northern Plains, the following are the lowest readings now showing up on the 12z MEX MOS for select cities:<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Portland: 18\u00b0<\/span><\/p>\n

Seattle: 20\u00b0 (with one subfreezing high)<\/span><\/p>\n

Spokane: -1\u00b0 (with a high temperature as low as 13\u00b0)<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Parts of Montana will likely experience recordbreaking cold. The following are the MEX MOS forecasts for Havre and Jordan with records for lowest\u00a0daily maximum and minimum temperatures in parentheses.\u00a0<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Havre:<\/span><\/p>\n

12\/5: High: -14\u00b0 (-12\u00b0, 1880); Low: -27\u00b0 (-27\u00b0, 1956)<\/span><\/p>\n

12\/6: High: -17\u00b0 (-15\u00b0, 1972); Low: -32\u00b0 (-31\u00b0, 1972)<\/span><\/p>\n

12\/7: High: -6 (-19\u00b0, 1927); Low: -37\u00b0 (-33\u00b0, 1927)<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Jordan:<\/span><\/p>\n

12\/5: High: -11\u00b0 (-12\u00b0, 1880); Low: -29\u00b0 (-27\u00b0, 1956)<\/span><\/p>\n

12\/6: High: -17\u00b0 (-15\u00b0, 1972); Low: -40\u00b0 (-31\u00b0, 1972)<\/span><\/p>\n

12\/7: High: -8 (-19\u00b0, 1927); Low: -37\u00b0 (-37\u00b0, 1927)<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Jordan has had only 5 prior readings of -40\u00b0 or below in December, the last of which occurred on December 31, 1992 (-40\u00b0F)<\/span><\/p>\n

 <\/p>\n

************************************************************************************************************************************************<\/p>\n

Posted Monday, December 3 @ 12:06 AM<\/abbr><\/strong><\/span><\/p>\n

Cold Air Now Arriving in the Pacific Northwest, Does Snow Lie in the Future?<\/strong><\/span><\/p>\n

\u00a0<\/span><\/p>\n

At 10 pm PST, the temperature at Seattle stood at 37\u00b0 and is likely to approach or reach freezing by morning. Even colder readings will occur during the following days.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Now that the much anticipated cold air is arriving, the all-important question concerns whether it will snow. Both the 12\/2 18z and 12\/3 0z runs of the GFS have suggested the potential for an extended snowfall event. The GFS Forecast and Reforecast ensembles have both had a precipitation signal for some time.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

\"Pac_NW12022013.jpg\"<\/p>\n

 <\/p>\n

In addition, the December 2008 cold outbreak, which has shown up in multiple runs of the GFS ensembles’ objective analogs and in the partial teleconnection cases, featured two weeks of cold, along with snow. From December 13 through December 26, 13.9″ snow fell. The biggest storm dumped 6.6″ during the 12\/20-22 timeframe.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

The synoptic pattern is very likely to feature an EPO-\/PNA- combination through at least the first two weeks of December. Such a pattern accounts for the overwhelming share of Seattle’s 6″ or greater snowstorms. The AO, which is highly important when it comes to Mid-Atlantic snowstorms is much less of a factor in the Pacific Northwest.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Below are a scatter diagram, AO\/PNA and EPO\/PNA charts for Seattle’s 6″ or greater snowstorms.<\/span><\/p>\n

 <\/p>\n

\"Seattle6inchsnowstorms.jpg\"<\/p>\n

 <\/p>\n

Needless to say, such a pattern does not guarantee snowfall, but it is the kind of pattern that is most favorable for such events. Odds probably favor at least some accumulation of snow in Seattle and Spokane and possibly Portland before the cold period ends.<\/span><\/p>\n

 <\/p>\n


\n************************************************************************************************************************************************<\/span><\/p>\n

Posted Monday, December 2 @ 12:30 PM<\/abbr><\/strong><\/span><\/p>\n

 <\/p>\n

Strong Cold Shot Imminent in Pacific Northwest & Northern Plains:<\/strong><\/span><\/p>\n

\u00a0<\/span><\/p>\n

This morning, the PNA was -2.055, its lowest value since September 28, 2013 when the PNA stood at -2.228. The current EPO-\/PNA- pattern is one that favors cold in the Pacific Northwest, as well as parts of the Northern Plains. Not too surprisingly, the cold that has been showing up on the operational guidance and ensembles for some time is now imminent for that part of North America.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

The latest values from the MEX MOS, GFS, and ECWMF for Portland, Seattle, and Spokane are below:<\/span><\/p>\n

 <\/p>\n

\"12022013.jpg\"<\/p>\n

 <\/p>\n

In addition, even as the ensemble guidance continues to show cold anomalies of 2-3 standard deviations below the norm in that part of North America, they show a brief shot of warmth across the Gulf States and Southeastern U.S. of around 2 sigma. Even more impressive, parts of Mexico are forecast to have readings around 3 standard deviations below normal during the December 4-6 timeframe.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Following the first week in December, some of the cold remains likely to push south and eastward with cold anomalies encompassing a large part of the CONUS, in addition to Canada at times. Some storminess could coincide with the arrival of the cold air producing at least some opportunities for snow. The greatest chance for mostly or all snow would probably exist in interior sections of the northern Middle Atlantic region, across central and upstate New York and into interior and northern sections of New England.\u00a0For now, it is too soon to worry about details.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

In the longer-range, the all-important question concerns whether the EPO will go positive, possibly in the face of a predominantly positive AO. The outcome has yet to be resolved, but that outcome could have an important influence on how things evolve after mid-December in the CONUS. Canada would likely hold onto the cold for a longer period of time.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Finally, when it comes to November, the 2008 teleconnection case proved to be the closest match for the actual outcome.<\/span><\/p>\n

 <\/p>\n

\"November2013_Final.jpg\"<\/p>\n

 <\/p>\n

From reading messages on various message boards, it seems that there is some misconception, at least among the general public, when it comes to cases or “analogs.” Such cases or analogs do not, and the emphasis is on “not,” seek to provide perfect or near-perfect forecasts. The role of analogs is to provide some measure of insight rather than exact details. Hence, one could reasonably state that from given patterns similar to the expected one, the eastern U.S. proved colder than normal or much of Europe proved warmer than normal. One should not state that Philadelphia or Paris would be colder\/warmer than normal, but that probabilities might favor certain outcomes. Perhaps a reasonable analogy is a legal case. One might draw upon a landmark decision to gain insight into how a court might rule in framing one’s arguments. Yet, the exact nuances of the case (or a judge’s subjective evaluation e.g., judicial philosophy)\u00a0might lead to a different outcome. The same holds true with respect to analogs in forecasting. Hence, they are not a subsitute for ensembles or other guidance. They complement it.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Going back to the above maps, one can see that the 2008 case provided a lot of insight into how things actually worked out. Nevertheless, they were far from perfect.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

Another note is also important. Developing analogs requires assumptions about the variables one uses. If the assumptions are reasonable, one might gain decent insight. But there is always uncertainty whether it comes to ENSO, the teleconnections, or other variables one incorporates. Hence, the assumptions might be off leading to a bad outcome. The same also holds true with modeling. As data becomes clearer, model outcomes may change markedly, sometimes on a run-to-run basis (often a signal of high uncertainty). That aspect of modeling is one of the reasons ensembles have become so important. Ensembles allow for tweaking of variables (a form of sensitivity analysis), hence one can analyze alternative outcomes and also take a look at the ensemble means (a composite based on the various scenarios). The spread in ensemble solutions can offer insight into the degree of uncertainty.<\/span><\/p>\n

 <\/p>\n

************************************************************************************************************************************************<\/p>\n

Posted Sunday, December 1 @ 11:35 PM<\/abbr><\/strong><\/span><\/p>\n

Evening thoughts…<\/span><\/p>\n

\u00a0<\/span><\/p>\n

1. The cold air mass that will be surging into the Pacific Northwest and Northern Plains in coming days is now showing up on the global temperature anomalies chart.<\/span><\/p>\n

 <\/p>\n

\"Temperature_Anomalies12012013.jpg\"<\/p>\n

 <\/p>\n

2. There are growing signs on the ensembles that the strong EPO- will either relax or give way to an EPO+ regime just after mid-month. The duration of such a change, if it occurs, remains uncertain. But at least a brief regime change would be likely against historical parameters.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

3. If that change occurs when the AO is positive or strongly positive, much milder weather could overspread the CONUS, though some lag between the date the EPO went positive and the onset of the milder pattern would be plausible.<\/span><\/p>\n

 <\/p>\n

************************************************************************************************************************************************<\/p>\n

Posted Sunday, December 1 @ 1:56 PM<\/abbr><\/strong><\/span><\/p>\n

\u00a0<\/span><\/p>\n

Continuing the focus on the Pacific Northwest, below are the GFS ensembles and also forecast PNA.<\/span><\/p>\n

 <\/p>\n

\"Pac_NW12012013.jpg\"<\/p>\n

 <\/p>\n

Ahead of the possible press of cold air toward the East, there could be a day or two of much above normal temperatures in the East, particularly the Southeast. The above frame from the GFS ensembles shows an area of\u00a0 2\u03c3\u00a0anomalies. For reference, high temperatures that are 1\u03c3-2\u03c3\u00a0above normal for the December 1-10 period (1981-2010 period) range from 67\u00b0-76\u00b0. Low temperatures with similar departures range from 47\u00b0-56\u00b0.<\/span><\/p>\n

\u00a0<\/span><\/p>\n

One should note that the GFS ensembles are forecasting 850 mb temperatures. If there is precipitation and no sunshine, highs could be closer to 1.5\u03c3. Right now, that’s still 5-6 days away, but the idea that Atlanta might see a reading or two in the 70s (lower to possibly middle) during the first week of December and one or two nights with temperatures in at least the middle 50s or possibly a little warmer is something to watch for based on the ensemble forecast.<\/span><\/p>\n

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For purposes of reference, the 12z ECMWF forecasts a temperature of 21.5\u00b0C (71\u00b0F) and the 12z GFS forecasts a temperature of 20.9\u00b0C (70\u00b0F) on December 6.<\/span><\/p>\n

************************************************************************************************************************************************<\/p>\n

Posted Sunday, December 1 @ 12:54 PM<\/abbr><\/strong><\/span><\/p>\n

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Some quick afternoon thoughts…<\/span><\/p>\n

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1. The big story over the next 7-10 days will be the cold that will invade the Pacific Northwest and Northern Plains. GFS ensemble forecasts continue to show some temperatures 3 standard deviations below normal at the height of the cold.<\/span><\/p>\n

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2. Some of that cold will come eastward during the second week of December, though it does not appear to be a direct shot.<\/span><\/p>\n

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3. Some storminess could coincide with the cold’s approach late in the second week of December.<\/span><\/p>\n

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4. The PNA is forecast to remain negative through mid-month. Odds of a colder than normal December in the Pacific Northwest are fairly high given that pattern and the cold anomalies that will develop during the first half of December.<\/span><\/p>\n

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******************************************************************************************************************************************<\/p>\n","protected":false},"excerpt":{"rendered":"

Check out Donald Sutherland’s Winter Weather Column (December Updates). <\/p>

Continue reading<\/a><\/p>\n","protected":false},"author":1,"featured_media":3910,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[78],"tags":[],"class_list":["post-6051","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-written-blogs-dec-2013","item-wrap"],"jetpack_featured_media_url":"https:\/\/www.ezweather.com\/myblog\/wp-content\/uploads\/2012\/12\/AmericanWXForums_Sutherland.gif","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.ezweather.com\/myblog\/wp-json\/wp\/v2\/posts\/6051","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ezweather.com\/myblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ezweather.com\/myblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ezweather.com\/myblog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ezweather.com\/myblog\/wp-json\/wp\/v2\/comments?post=6051"}],"version-history":[{"count":6,"href":"https:\/\/www.ezweather.com\/myblog\/wp-json\/wp\/v2\/posts\/6051\/revisions"}],"predecessor-version":[{"id":6120,"href":"https:\/\/www.ezweather.com\/myblog\/wp-json\/wp\/v2\/posts\/6051\/revisions\/6120"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.ezweather.com\/myblog\/wp-json\/wp\/v2\/media\/3910"}],"wp:attachment":[{"href":"https:\/\/www.ezweather.com\/myblog\/wp-json\/wp\/v2\/media?parent=6051"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ezweather.com\/myblog\/wp-json\/wp\/v2\/categories?post=6051"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ezweather.com\/myblog\/wp-json\/wp\/v2\/tags?post=6051"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}