WEATHERAmerica Newsletter, Saturday, November 6, 2021 at 9:00 PM CT; Longer Term Forecast

[Larry Cosgrove]

EXTENDED PERIOD FORECAST

(Between Day 11 And Day 15)

 

An Amplified Jet Stream Configuration Around North America. But Cold Air Advance May Be Slow

CIMSS

NOAA/IMS (2)

InstantWeatherMaps.Com (2)

TropicalTidbits.Com (Dr. Levi Cowan) (3)

NOAA/PMEL

NOAA/CPC

ECMWF

HPRCC/University Of Nebraska (2)

Environment Canada

TropicalTidbits.Com (Levi Cowan) (5)

TrueWx.Com

 

While the upper air forecast may look distinctly more wintry, I would caution that this is not a severe winter weather scenario. For one thing, the blocking signatures are modest and somewhat scattered across the polar regions. Thus, there will be depression of the jet stream, but not to such extreme low latitudes that a cA or cAk regime would have easy transport to previously warm locations. The Sonoran hat ridge, for example, will cover most portions of the American West, but have only occasional interaction with positive height anomalies in Alaska, the Northwest Territories or Greenland.

That scenario may change as the 500MB longwave pattern shows important changes during the 11 - 15 day period. All of the model ensemble packages show retrogression of the Gulf Of Alaska Low into a position below the Aleutian Islands. At the same time, a full-latitude trough aligns from James Bay to Florida. The ECMWF and GGEM members link the ridge over the southwestern states with a counterpart in Alaska and the Yukon Territory (the GFS panels do not). An important point here is that these same versions have interaction of the subtropical jet stream from Mexico into the Bahamas, suggesting a surface cyclogenesis event in Georgia or South Carolina around November 22. Keep in mind that the Thanksgiving holiday weekend is just around the corner from that date. Even with a polar air mass (not Arctic), the lack of snow seen in the Midwest and Appalachia now might seem like a distant memory IF these features show up as advertised.

We are not quite in a true "winter configuration" just yet. But we are "getting there", so to speak. As I suspect that the introduction of a true sub-Aleutian Low is accurate, the chances for a colder alignment east of the Continental Divide are increasing. And while a warm-up could occur in the first week of December (CFS and ECMWF series hint at this in Week 4 predictions), I like what I am seeing. So far, the analog forecasts are looking very good for mayhem as we get into the heart of winter.

Prepared by Meteorologist LARRY COSGROVE on 
Saturday, November 6, 2021 at 9:00 P.M. CT

Disclaimer: 
The previous statements are my opinions only, and should not be construed as definitive fact. Links provided on this newsletter are not affiliated with WEATHERAmerica and the publisher is not responsible for content posted or associated with those sites.

Copyright 2021 by Larry Cosgrove

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