Rains and warmer weather this weekend on track/Thanksgiving looks cold/Milder pattern may open December

Not much has changed in terms of the thinking for this weekend’s rain event, best totals are expected over the eastern district, with skimpy totals over the western half.  As was mentioned yesterday, this might be the last best shot at picking up decent rains for the rest of November.  Cold and mostly dry weather readies a return for the lead up to Thanksgiving and the following busy first weekend of the holiday season. A weak system might generate a few flakes late next week, but that system looks weak and rather moisture-starved, at least at this point.  Let’s take a look at this afternoon’s suite of computer model guidance.  All of these images go through 6 PM Monday evening and you can click to enlarge any one of them:

2014-11-21-1050-12ZNAMTTP 2014-11-21-1053-12ZGFXTTP 2014-11-21-1245-12ZGFSTTP 2014-11-21-1250-12ECMTTP

As you can see, they are in reasonable agreement, except for the European (ECMWF) model which continues to be deeper, more generous with rain totals and further west that the U.S. NAM, GFS and GFSx models. The GFSx model is very dry, comparatively, with all areas less than 1/2″.  A blend of the NAM/ECMWF model looks best with totals of 1/4 to 1/2″ in the KC/Topeka area, and from around and inch to up to an isolated 1.5″ for STL/SEMO/SW IL.  No worries about snow or ice; we’ll see temperatures rise into the 50s and perhaps near 60 for this event, with lows remaining in the 40s.  One thing to watch out for is fog- as the warm moist air runs over the cold ground, it will cool and condense, so there may be patches of locally dense fog around this weekend.

Rain will be light, spotty to scattered in Topeka throughout this weekend, with the most activity Saturday night and Sunday morning.  For KC, rain will be scattered and light except for Saturday night and Sunday when widespread light to moderate rain will fall, and that may last into Sunday night.  In St. Louis, SE MO & SW IL, scattered rain tonight becomes widespread Saturday through Sunday night, scattering out and ending early Monday.

Turning our attention toward Thanksgiving and the following long holiday weekend:  The good news is that there still appears to be no threat of any major storm systems; the bad news is that we appear to be headed for another Arctic blast.  A strong cold front looks to pass through mid week (Wednesday or so-timing subject to change) with temperatures in the 30s for highs Thanksgiving.  If that front slows down, it might be warmer.  There may be a few spot showers or flurries with and behind the front, especially for eastern areas of the district, but no travel issues.  Mostly sunny skies are expected with perhaps a few high clouds for Thanksgiving. Clouds may increase Thursday night into Black Friday as warmer air begins to build back in.

Right now this appears to be the signal of a change in the overall pattern as we enter December.  Look at the forecast jet stream pattern we have on Thanksgiving Day:


This is a pattern we got very familiar with last winter.  A big ridge of high pressure over Alaska and one on the west coast.  This has kept Alaska and the west quite mild while we’ve been very cold.  The jet stream flows into the Arctic and then carries the air south into the U.S.


Now take a look at the forecast pattern for December 1st.  The Alaskan ridge has backed off to near the Dateline and a cool storm has replaced the ridge off the west coast.  That ridge has edged east into the central U.S.  That brings us mild and dry Pacific flow, cutting off the Arctic. Keep in mind average highs in early December are only in the low 40s, so “mild” is not shorts and tank top weather by any means.  Most long range charts and indexes we look at are expecting a pullback of the bitter cold at least into the first week or so of December.  This has support from history. When we look at the historical record for years in which ocean surface temperatures, regions of warmth and cold in the oceans are similar to current patterns — and what has happened so far this year — we find some similar matches.  All featured a retreat of the cold into December.   The bad news is that all of those similar years also featured a return of the cold with a vengeance by the end of December into January and February.


We’ll get more into the winter outlook next week.  Keep in mind these forecasts (Thanksgiving to December 1st) are at the far end of the forecast period so there may well be some adjustments to the cold and follow-on moderation as we look at new data early next week.


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