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There is your low level arctic bleed moving SSE at hour 324 and beyond as the + EAMT seems to be relaxing for a time and things start to noticeable improve in the Pac. You have same incredibly cold air over in Eurasia.

@poolz1 Ramping up

WOOF also very active to say the least..... snow on snow

920 mb, Wow !

Pac is coming along. Damn, sweet progression mid month.

@poolz1 pretty neat

I love this animation, really hope the GEFS has the right idea. Its beautiful ! The GEFS has been doing well overall, so hopefully this wave retrogression is correct.

Euro pretty firm on Jan 5 th. Getting closer.

Coming soon to CAPE's backyard.

Today there is increased consensus on keeping the AO negative near - 3 SD for an extended period of time, possibly even lower towards mid Jan.

Hopefully the last cutter for a while afterwards, if the GEFS is correct. Then, we track the various impulses moving under the block as the pattern continues to improve. Looks like exciting tracking opportunities from mid Jan into Feb. I would speculate, as you ,mentioned, real threats for our area start near the 14 th or 15 th. In the past there have been multiple times when we scored with a so so Pac, but a stellar -AO and - NAO.

Hmmm......

I like the sound of this, a huge player for sure.

HL becoming more negative as indicated by the blue colors, this increases over time. A very positive factor for eventual cold and snow in the East.

NAM state improving.

If you want to play voodoo outcomes, lets say the SSWE officially triggers on the 5 th of Jan, ( per the Euro ) the cold would not become evident in the East until near January 25 th to Feb 1 st. The map above is only January 8th. Also, keep in mind if the Urals High re-builds we will continue to get +EAMT events.

Euro has official wind reversal much sooner than the GFS. GLOSea supports the Euro. Faster official SSWE would mean effects time line moved up. @SimonLeeWx Replying to @SimonLeeWx GEFS & CFSv2 have 64 vertical levels, while ECMWF's ensemble has 91 and more of those are in the stratosphere (38 above 100 hPa vs. 24 in CFS). So, I anticipate ECMWF is on the right lines, as models with greater vertical resolution perform better (https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019JD030920…) [2/2] The ensemble-means of ECMWF extended, GEFS 35-day & CFSv2 all produce a major SSW during January - but they are really predicting different events, since while ECMWF reverses ~Jan 5, GEFS (Jan 12) & CFS (Jan 22) reverse much later! Which will be correct? [1/2]

Do you still feel the Pac will improve in late Jan? I mean beyond periodic + PNA intervals. This area is another area of various conflicting views from mets and pros.

Looking at 500 certainly makes you think that NA gets the benefits of the SSWE. And speculation would suggest the cold air continues to gather and deepen past this time frame. Also, some off the climo charts possibilities exist down the road, with the incredible low pressure storm system in the North Pac and a possible world breaking high pressure reading yesterday.

Seems like conflicting views and opinions, even from various well respected mets regarding the - NAO/block/ AN heights near and around Greenland. Some say what tombo stated, others are gung-ho about real storminess and snow prospects in the East.

Great thread. Worth a read. Way more to.it than what I posted. Anthony Masiello @antmasiello · 1h A tradition of sorts: to take the ECMWF zonal wind anomaly charts during a SSW and show the zero-line descend through the stratosphere. GIF @antmasiello · 1h **correction, that is not a zonal wind anomaly but mean zonal @antmasiello Replying to @antmasiello the mean zero-wind line determines the level at which future waves break (RW can only upwell through westerly flow) and deposit their easterly momentum. The descent in this one seems quicker than usual, but I do not have numbers to back that up. 12:06 PM · Dec 28, 2020·Twitter Web App @webberweather · 1h Replying to @antmasiello JRA-55 SSWE compendium composite shows the zonal wind reversal propagating from the stratopause to ~20mb in a matter of 3 days (ish) during major sudden warming. Looks about right to me @antmasiello · 1h thanks for the composite, and your conclusion is probably right, but that doesn't show the zero-line reaching the 50-100mb depth, probably from event smoothing.

No time for greater detail but, wow to the new AO and NAO ensemble forecasts. Really diving down, looking better and better for a SECS based solely on those 2 indicates moving forward into January.

The Ural blocking has diminished by hour 576 ( accept at own risk ) which was responsible for the East Asian Mountain torque. Hopefully models go to a more robust + PNA , and post the SSWE we may get the vortex to settle further South in time. May seed areas to our NW with a very cold air mass by the third week of Jan.