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Met Winter 20-21: Pattern Drivers & Evolution


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While there's reasonable agreement on a -AO and -NAO persisting into early January, there is some uncertainty WRT whether or not the Pacific side offers any help or not. The EPS develops a +EPO into e

I'm starting to get a little more excited for early-mid December. It looks like the Pacific jet will retract significantly, which is the real reason for the retrograding Alaskan LP. Upper level diverg

I think that we are going to see a pretty impeccable 500mb pattern after January 10th.    The -NAO originally forced by wave breaking (which is occurring in the very near future) will become

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Through today, New York City has received no snowfall. Winter 2020-21 is the 18th case on record during which New York City had seen no snowfall through December 6. For the prior 17 cases, mean winter snowfall was 19.9". The most snowfall occurred during winter 1870-71 when 33.1" was measured. The least snowfall occurred during winter 2001-02 when just 3.5" snow fell. Records go back to 1869.

 

Through mid-week, temperatures will run somewhat below normal. Milder weather will return for a time afterward, before the next push of cooler air arrives. Through mid-December, no exceptional cold is likely.

 

Meanwhile, another round of near record and record warmth is likely in parts of western Canada through mid-week.

 

A warmer pattern could begin to develop toward the winter solstice. The closing 10 days of December could wind up generally warmer than normal. The EPS weeklies and new subseasonal guidance are in strong agreement that the last week of December will likely be warmer than normal. The duration of the current AO-/PNA+ pattern will be key to how long the developing colder pattern persists.

 

Statistical guidance based on the ENSO state and teleconnections would typically favor a colder regime for the first half of December in the Middle Atlantic and southern New England regions. Both historic experience following exceptionally warm November cases suggest that a warmer than normal December remains the base case even if the first half of the month winds up colder than normal. Almost 90% of cases with a November mean temperature of 51.5° or above in Central Park (2020 saw the temperature average a record 52.9° in November) went on to record a warmer than normal December and just over three-quarters of such cases saw December register a monthly mean temperature of 40.0° or above.

 

The ENSO Region 1+2 anomaly was -1.0°C and the Region 3.4 anomaly was -1.0°C for the week centered around November 18. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.87°C and the ENSO Region 3.4 anomaly has averaged -1.40°C. La Niña conditions will likely prevail at least through the winter.

 

The SOI was +11.78.

 

Today, the preliminary Arctic Oscillation (AO) figure was -1.324.

 

On December 5 the MJO was in Phase 4 at an amplitude of 1.023 (RMM). The December 4-adjusted amplitude was 1.020.

 

Based on the latest guidance, no significant stratospheric warming event is likely through the first two weeks of December. The warming above 3 mb in response to recent strong Wave 1 activity could abate toward or just after mid-month.

 

Since 1950, there have been five cases where a La Niña developed during June-July-August or afterward following an El Niño winter. 4/5 (80%) of those cases saw a predominant EPO+/AO+ winter pattern. The most recent such case was 2016-17. 10/11 (91%) of the La Niña winters that followed an El Niño winter featured a predominantly positive EPO. A predominant EPO+/AO+ pattern is very likely for winter 2020-21. It is likely that the Middle Atlantic and southern New England areas will see a warmer than normal winter with below normal snowfall.

 

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2 minutes ago, 33andrain said:

This would definitely leave a mark. Actually starting to get a little excited tbh.

 

gfs_Tz10_nhem_fh240-384.gif

Keeping my fingers crossed! Might be the only way to save Winter. 

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10 minutes ago, 33andrain said:

A potent warming attack on the PV at 10mb making it weaker. I just want the PV to experience sustained warming attacks through December, so that we can get the job done maybe in early Janaury and potentially look forward to a second half winter.

@33andrain thanks that would be awsome

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18 minutes ago, 33andrain said:

A potent warming attack on the PV at 10mb making it weaker. I just want the PV to experience sustained warming attacks through December, so that we can get the job done maybe in early Janaury and potentially look forward to a second half winter.

The million dollar question is where does the cold go On the West Coast ,East Coast Europe what do you guys 🤔 

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8 minutes ago, bird said:

The million dollar question is where does the cold go On the West Coast ,East Coast Europe what do you guys 🤔 

well hopefully the warming is sufficient to obliterate the PV so we can all join in on the fun.

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Finally, some positive news may not need a Major SSW to save Winter afterall. Thanks and credit goes to Met DT. This is hot of the presses!!!

 

 

 

  IN MAJOR   DEVELOPMENT    the  ecmwf    enso model shwos   DRAMATIC  WEAKENING  of the Moderate  La Nina.

It is hard to understate   how  BIG  this is...or   COULD be... 

 a   rapidly  weakening   La Nina...   in essence a   WEAK  La nina combined with  SSW   EVENT

 t 

unnamed.png

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1 hour ago, 33andrain said:

This would definitely leave a mark. Actually starting to get a little excited tbh. Trending stronger and moving up in time.

 

gfs_Tz10_nhem_fh240-384.gif

 

 

But But But...the 500mb LR / Weeklies pattern says TORCH! 

 

(hope someone sees my sarcasm here) 

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24 minutes ago, leo2000 said:

Finally, some positive news may not need a Major SSW to save Winter afterall. Thanks and credit goes to Met DT. This is hot of the presses!!!

 

 

 

  IN MAJOR   DEVELOPMENT    the  ecmwf    enso model shwos   DRAMATIC  WEAKENING  of the Moderate  La Nina.

It is hard to understate   how  BIG  this is...or   COULD be... 

 a   rapidly  weakening   La Nina...   in essence a   WEAK  La nina combined with  SSW   EVENT

 t 

unnamed.png

 

Wait. I was told it was moderate strong last night. 😃 

 

(again, hope some see the sarcasm) 

 

If you have a La NINA weakening at the rate this suggests, along w/ a SSWE event occurring - your 500mb LR models are going to be wrong. 

 

Now, if the models are sensing this is data, and trends, are errors. Then, okay - I am wrong and and what the models are suggesting are correct. I just don't believe that will be the case. 

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1 hour ago, RAllen964 said:

 

 

But But But...the 500mb LR / Weeklies pattern says TORCH! 

 

(hope someone sees my sarcasm here) 

With a unfavorable mjo and -AAM it’s not a slam dunk we get cold in a weakening vortex 

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  • 33andrain changed the title to Met Winter 20-21: Pattern Drivers & Evolution
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