GaWx

Based on major snowfalls at RDU, CLT, and ATL, the requirement of a -NAO at the time of the storms is often exaggerated. The existence of a +PNA has been much more important.

I went from a nasty cold rain (low 40s) in Atlanta around lunchtime to 75 and PC/no rain here in SAV now! I’m now warm in my cords/flannel shirt. Always fascinating to see such changes when driving.

GEFS NAO 2 days ago: Today: @snowman19 @donsutherland1

What’s your Dec MJO prediction? What’s your Jan PNA prediction? I expect a +PNA due to all -ENSO PNA Decs since 83 transitioning to Jan +PNAs.

11/30 MJO 2 week runs 11/30 EPS: steady as can be (4th day in a row very similar) phase 8 12/3-14+, which would be the longest phase 8 in 50 years for any winter month! To show how consistent it has been, the EPS had this on 11/27 run, phase 8 12/3-11+: ————— GEFS 11/30 (not as consistent as EPS, which has been doing better with phase 7 than GEFS): also has phase 8 start Dec 3rd: JMA 11/30: phase 8 12/3-10+

Euro Weeklies 46 day 2m temp anomalies: 11/25 run: NYC and Chicago -3F 11/29 run: NYC -6F, Chicago -8F (would be coldest in many years for that period) Euro seasonal winter fcast issued Nov 1st: huge warm bust potential increasing, which could end up like last winter or even worse:

Although only barely, it’s now confirmed that we on 11/28/2025 just had the earliest major SSW (reversal) since 11/27/1968 with the zonal wind a whopping 30 m/s BN despite it only barely reversing: Kudos to the Euro Weeklies mean of 100 members predicting the weakest point of the SPV to the day a month before it occurred: This reminds me of the models being initially oblivious to the upcoming -NAO/-AO that appeared after the 2/16/2023 major SSW: EPS 11/25 12Z run: all +NAO EPS 11/30 0Z run: almost all -NAO including as early as Dec 4th, when 11/25 run had +NAO Similar comparisons for AO: EPS 11/25 12Z run: EPS 11/30 0Z run: like night and day

MJO from today’s 2 week runs: both now have 11+ day long phase 8s, longest since Feb 2010 and longest Dec since 1975. Lots of potential in 1st half of Dec and beyond! GEFS is all in 8 12/3-13 vs yesterday’s 7 for same period: EPS is same as yesterday:

Back down to neutral NAO/AO week 2 similar to 2 days ago:

1. EW 12/15-21: large change in just 3 days: will it hold? 11/25 run: 11/28 run: —————— 2. EW 12/8-14: huge change in just 3 days: will it hold? 11/25 run: 11/28 run: ————— 3. EW 12/1-7: huge change in just 3 days 11/25 run: 11/28 run: —————- -NYC has cooled from +1F to -4F for the 3 week period in just 3 days. -They now have NYC at -3F for Dec as a whole, which is ~36-37F. Similar cold ENSO Decs were in 1954, 1964, 1966, 1975, 1981, 1988, and 2007.

12Z EPS held into the cold partially because of this:

For Dec 1-10: 12Z EPS held onto its 0Z significantly colder temps vs 0Z GEFS. But also, 12Z GEFS came in significantly colder than 0Z GEFS: 0Z GEFS: 12Z GEFS: colder/in EPS direction: 12Z GEPS came in much colder than 0Z GEPS: 0Z GEPS: 12Z GEPS: colder than 0Z GEPS Edit: NG is up 7% on the colder model consensus.

12Z GEFS is coming in significantly colder than the 0Z for week 2:

Indeed, after doing poorly with phase 6, the EPS absolutely was doing much better than GEFS getting into phase 7 between the 11/15 and 11/18 runs: 11/15 EPS: poor for 6; much better for getting into 7 11/15 GEFS: great for 6 but bad for getting into 7 (way too slow as 7 actually started on 11/27): Similar comparisons for 11/17-8 runs: 11/17 EPS: almost spot on with 11/27 ph 7 timing: 11/17 GEFS: still not in 7 on 12/1 11/18 EPS: great with ph 7 11/18 GEFS: not into phase 7 til 12/2, 5 days too late Edit: 12Z GEFS coming in significantly colder than prior runs

Related to this, check out the differences in the means (green) between the +AO of the 0Z GEFS and the slight -AO of the EPS: GEFS: EPS: