Wintry Winter 25-26 Winter Battle Zone

[griteater]

Someone jog my memory without having to dive deep into past Forums, but the last disruption of the polar vortex happened in December of last year right? then we had the few week lag period which gave us the active Winter storm pattern in January. But the actual event happened in the December correct?

Also, how well did guidance forecast the disruption last November for December?

The SPV was actually stronger than normal all last winter and we had the big cold blast in Jan. Last winter was a bit unusual though as there was a big disconnect between the troposphere and the stratosphere. Sometimes that happens though.

But the strat is just one tool in the toolbox. It's difficult though to have prolonged Greenland blocking episodes if the lower stratosphere (100mb) isn't weaker than normal, so that's what we're shooting for.





Here's the image from 2010-2011. Can see the weaker than normal lower stratosphere from mid-Nov to late Jan

 

[Mitch West]

The SPV was actually stronger than normal all last winter and we had the big cold blast in Jan. Last winter was a bit unusual though as there was a big disconnect between the troposphere and the stratosphere. Sometimes that happens though.

But the strat is just one tool in the toolbox. It's difficult though to have prolonged Greenland blocking episodes if the lower stratosphere (100mb) isn't weaker than normal, so that's what we're shooting for.

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Here's the image from 2010-2011. Can see the weaker than normal lower stratosphere from mid-Nov to late Jan

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Ahhh got ya. I thought there was connection to what was mentioned above. Totally wrong I guess! haha

 

[griteater]

Here are the 5 Cool ENSO / La Nina Decembers since the late 70's that had a coherent MJO wave roll out of Phase 7 and into 8-1-2 (with varying levels of amplitude) which is what I think we are going to see this December (but no guarantees of course). Each one was cold to very cold east of the Rockies

 

[GaWx]

Here are the 5 Cool ENSO / La Nina Decembers since the late 70's that had a coherent MJO wave roll out of Phase 7 and into 8-1-2 (with varying levels of amplitude) which is what I think we are going to see this December (but no guarantees of course). Each one was cold to very cold east of the Rockies

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Hey Grit, very nice analysis!

I want to ask you about whether you should consider adding two other Decembers:

1. 1981:
- like 1985 and 1989, ENSO was cold neutral
- On the MJO chart below, you can see it coherently went from 7 to 8 to 1 in the 2nd half of Dec. Then in Jan it moves out of 1 into 2 on Jan 5th with Jan 7th the last day in phase 2. So, a good portion of this was in Dec.

Dec:


Jan:


2. 1974:

- was La Nina
- this was the first Dec. for which MJO data was available. There’s no chart for it, but the text is there. I copied 12/16-30 because it shows that that period started in phase 7 and then coherently went through 8-1-2 (with mainly moderate intensity) 12/20-29:

1974 12 16 -0.57059002 0.59700698 7 0.82582700 WH04_method:_OLR_&_NCEP_wind
1974 12 17 -0.48232999 0.69856101 7 0.84890199 WH04_method:_OLR_&_NCEP_wind
1974 12 18 -0.36357000 0.71566701 7 0.80272198 WH04_method:_OLR_&_NCEP_wind
1974 12 19 -0.50213999 0.67306399 7 0.83973598 WH04_method:_OLR_&_NCEP_wind
1974 12 20 -0.94752997 0.73516202 8 1.1992800 WH04_method:_OLR_&_NCEP_wind
1974 12 21 -1.2667900 0.49437299 8 1.3598400 WH04_method:_OLR_&_NCEP_wind
1974 12 22 -1.4928600 0.41040900 8 1.5482500 WH04_method:_OLR_&_NCEP_wind
1974 12 23 -1.4189500 -0.18106000 1 1.4304500 WH04_method:_OLR_&_NCEP_wind
1974 12 24 -1.4376301 -0.36104000 1 1.4822700 WH04_method:_OLR_&_NCEP_wind
1974 12 25 -1.3505800 -0.54887998 1 1.4578600 WH04_method:_OLR_&_NCEP_wind
1974 12 26 -1.0854100 -0.86048001 1 1.3851200 WH04_method:_OLR_&_NCEP_wind
1974 12 27 -0.72742999 -1.0168999 2 1.2502900 WH04_method:_OLR_&_NCEP_wind
1974 12 28 -0.49579999 -0.72926003 2 0.88183898 WH04_method:_OLR_&_NCEP_wind
1974 12 29 -0.26330999 -0.53425997 2 0.59562302 WH04_method:_OLR_&_NCEP_wind

 

[hendrik]

Just did ~an hour and a half of some good old number crunching (referring to my earlier message). While doing that I made a spreadsheet with the combined daily pna, nao, and ao values all together, which (to my knowledge) was not readily available before, so there's that.

For the sake of my sleep schedule the write-up will have to wait until tomorrow, but it should be interesting at least. I'll include the resources in there if anyone would like.

Starting to seem like the pieces are really coming together for a productive winter down here. Fingers crossed.

 

[SnowNiner]

Thing about December is that we have a lot of things on our side right now.

1. La Nina climo
2. La Nina / -QBO
3. Weaker than normal SPV
4. Favorable MJO

All of those favor colder than normal temperatures. The whole month may not average cold, but it would be an upset loss if we don't see a good chunk of it colder than normal

Here's today's SPV zonal wind chart. Can see how the SPV is weaker than normal into late Dec. Hopefully, the more important lower strat at 100 hPa (100mb) is even weaker than what is showing here as that would help promote blocking episodes

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Thanks Grit! I’m pretty convinced we’re in for a decent December considering all the things we have going for us, especially with the likelihood of the MJO progressing in a way the leads to favorable pacific. You and Webb have given a lot of evidence that we’re on the right course there. That in itself is enough for me to have positive expectations, and I really appreciate those valuable insights.

Im just trying to temper my excitement considering past periods that seemed to have so many elements going for it only for things to fall apart. Was it 2 February/Marchs ago? I remember similar positive expectations that didn’t pan out. The mjo didn’t progress, the jet didn’t cooperate and we ridged and torched. But that’s every February and March now.

Keeping hope alive!

 

[GaWx]

There are 5 major SSW events on record between Nov 24th and Dec 7th:

-1958
-1965
-1968
-1981
-1987

Here’s the Dec temp. anomaly map: E US mainly 1-2 F BN


Here’s the Jan temp. anomaly map: E US mainly 2-4 BN, which incorporates extreme cold in places during 1966 (late), 1982 (mid) and 1988 (early):


Here’s the Feb temp. anomaly map: E US NN


So, the coldest month regarding E US anomalies was Jan and the warmest was Feb. Feb. might have been even warmer (warmer than normal) had 4 of these 5 winters not been during El Niño, which tends to favor cold in the 2nd half of winter vs La Nina’s colder 1st half.

All of this is telling me that should the late Nov major SSW actually occur, the coldest month in the E US could easily be Jan rather than Dec, which makes sense considering an assumed several week lag. But, of course, that would remain to be seen especially considering La Niña often favoring Dec as the coldest anomalywise.

https://www.researchgate.net/figure/The-SSW-and-SFW-event-onset-date-year-and-type-identified-in-the-NCEP-NCAR-dataset-The_tbl1_267063738