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GEFS trends continue to get colder and the extreme departures are moving East.

Another reinforcing drop in the - AO towards day 7 through 9.

@bluewave since we are getting deeper into December would that association, with the - 4 AO and the block North of Alaska, work for areas near Baltimore and Wilmington, DE. regarding snowfall ? Thanks

Oh my, unreal and eerie

Siberian Express and snow too

Well, this is a great thread by Allan where he provides composites of the 500 mb anomalies and surface tempertures based on the CPC super ensembles then rolled them forward 5 days from Dec 22 nd to Dec 27 th and then another 5 days centered on 1/1/23. Wow !!! HM chimes in at the end.

Agreed, that was my point. Certainly appears we are entering a long duration negative AO regime. This will also be the first December in many years where the robust snow cover extent in North America didn't go poof after December 20th. A healthy cryosphere, a good sign.

Compared to yesterday's AO forecast it shows less likelyhood of nearing - 1.0, also less spread. Here is yesterday's forecast. Here is today's.

Improvements out West really showing up on the modeling. The looks might continue to improve in the days ahead. Real winter weather in the East is fast approaching.

The AO is trending more negative further out in time. Looks really nice up top.

Nice animation and discussion by @griteater

Very active pattern weather pattern coming up between December 20 th and Jan 15 th. Massive arctic airmass pooling in Western Canada by day 8 to 10 and disturbances focused near our area, mostly undercutting the block, hybrid coastals and eventual clippers are possible. The Pac improves as we move deeper in December. Snowcover continues to expand South and East over time increasing the odds of min. temps falling to near 10 degrees at some point after the arctic passage(s) later in the month. Blocking wants to recycle in the EPO and NAO domains. We already achieved a statisical significant - 4.0 AO SD to add to this continuaton of HL blocking. You can see that here: https://www.cpc.ncep.noaa.gov/products/intraseasonal/z500_nh_anim.shtml

National temps on December 26 th using a blend of the GEPS, GEFS and EPS. Brrr.....

Everything considered, including comments from several media outlets regarding frigid conditions in the East near Christmas, its not really that cold. We had colder already, teens as low temps were recorded at many locations. That was when we had the record - EPO a while back.

Can you imagine if we get snow cover prior to this arctic beast. What an opposite December from the last 10 years. It does look like a 1960's type winter pattern for a period of time, leading up to and most likely going past the first of the year.

Interesting CPC D+ 11 Analog Composite. Notice the years from the 1960's, 1970's. I believe @Bob Chill mentioned he was looking at 1960's type winter comparisons for this winter.

Well we did it ! Achieved a - 4.0 SD on the AO. Good times should follow. https://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/norm.daily.ao.nao.pna.aao.gdas.120days.csv The AO looks to remain negative.

Expect some crazy outcomes late week as the jet reverses.

Yep, it looks really cold, and it may have staying power as the - AO regime looks to remain in control. Snowcover will help with the overall cold expanse.

From the book Kocin and Uccellini, there is potential ! I have sinned, forgive me for posting this .

OMG the Holly Grail of Blizzards is a coming................................ Split flow !!! Blocking !!! Arctic Air !!!!

Of potential interest in regards to HL blocking today is the AO might achieve a -4.0 SD . Yesterday I believe it was - 3.35 or close to it. According to Don Sutherland when the AO achieves - 4.0 or deeper reading it has the ability to overpower less friendly indices such as the - PNA. Not saying this is going to be the outcome, but it will be interesting to watch the trends. Also of the note, the AO is not forecast to rise as rapidly once bottomed out then what was modeled a few days ago. So, basically it appears the month of December will feature a mostly or completely negative AO and a significant one of that which will hopefully entices another - AO regime during the upcoming winter season.

Nice to see the moisture nearby with the cold in place.

The PV still looks to be under pressure as we near the end of the month with a couple heat fluxes.