Where Did the December Cold Come From? A Hypothesis

[donsutherland1]

After having examined a number of maps, it appears that there may have been a strong hint of abnormal cold relative to what the pattern seemed to be implying. While surface temperature anomalies were running above normal across Canada on December 1, 2003, 500 mb readings were running below to much below normal.

<img src="http://www5.wright-weather.com/bb/attachment.php?s=&postid=153387">

The stormy pattern might well have led to mixing so that the cold was not only pulled into the Eastern U.S. but also brought to the surface.

This is just a hypothesis at this point.

Also, another tidbit. Today, saw above normal 500 mb height anomalies hook up across North America. With evidence that this linking of heights could hold for a few days, it is important to note that this has often been a precursor or Arctic outbreaks 7-14 days down the road when the pool of cold air has been expanding on our side of the North Pole.

With the ensembles suggesting that the Arctic Oscillation could go negative to strongly negative near the end of this month, there are strong suggestions that the pool of cold air will be moving onto our side of the North Pole and expanding in our hemisphere.

<img src="http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.sprd2.gif">
Current Ensemble Projections for the Arctic Oscillation

Teleconnections are also hinting at a possible Arctic outbreak with the cold first spreading down the Northern Plains and then spreading eastward. It should reach the East Coast in the 1/3-5/2004 timeframe.

With the high latitude blockiness that is increasingly showing up on height anomalies and the NAO, any storms ejecting out of the Gulf of Alaska trough will have to be watched carefully as they progress across the country. With each will come the risk of snow and ice, especially with the hints that the Arctic air could be pressing into the U.S. toward or immediately after the start of the New Year.

<img src="http://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/nao.sprd2.gif">
Ensemble projections for the NAO

Initially (the New Year +/- a few days), the greatest threat for snow or ice will probably lie across the Ohio Valley, northern Mid-Atlantic, and Northeastern regions. Such a threat could be pushed farther south once the cold air locks into place, perhaps not too dissimilar to the second half of January 2003.

Finally, with the strongly positive SOI since 12/19, it is possible that the evolving trough-ridge position locks in at around the time the possible Arctic cold arrives in the East. Thus, it would not be entirely surprising if a 1-2 week period saw readings run generally below to much below normal in the Eastern U.S.

[JCT777]

Great discussion Don. Thanks for posting it!

[PTrackerLA]

Very interesting stuff you've got there. I was worried December would be unusually warm just like November was but it has been pleasantly cold. Here's hoping for the real arctic chill in Jan 04!