GaWx

Wow! The chance for a major, and possibly even an extreme SSW in early Jan is even higher! On Jan 9th, the EPS mean of 101 members shows a mere 14 m/s vs climo way up at 35! There are so many members with a major SSW that it will be tough to count! This appears to be at a whopping 45%+ for a major, easily the highest yet beating yesterdays ~38%. Dates are from 12/25 through 1/16. This has ~~30% of the 101 members down to sub -10 m/s (vs 20 in prior run), 12 sub -20 (vs 10 in prior), 8 sub -25 (vs 4 in prior), and 2 sub -30 (vs none in prior):

More on the above. 2022, 2009, and 1985 were the only sub -2 AO 12/1-16, where 2023 is possibly headed. The most -AO winters in order were 2009-10, 1976-7, 1968-9, 1962-3, 1969-70, and 1985-6. So, 2 of the 3 most -AO 12/1-16 ended up within top 6 most -AO winters of 73 winters! Only 2022-3 didn’t. Of those 6, only 1962-3 and 1985-6 weren’t Nino but they were neutral. 2022-3 was a solid Niña. Not being La Niña and being El Niño changes things tremendously. Despite difficulty in getting -NAO winters since 1979, -AO winters haven’t been overly tough and this along with progs for weak SPV for at least first half of winter tell me that a -AO winter is now looking likely. Don’t know if that would drag the rare winter -NAO along with it, but that sure would increase its chances.

But big diffs -we're in El Nino (favor PNA) vs 2022's La Nina, which favors -PNA -there was record strong SPV late Dec 2022 vs progs for weak SPV late Dec 2023 -mid to late Dec was in warm MJO; then much of Jan-Feb was in strong often right sided MJO vs progs for weak left sided MJO late Dec into Jan

Per this GEFS prog mean, the 12/1-16 AO may end up the 2nd lowest to 2022 back to 1950. The only others that were sub -2 were 2009 and 1985. So, only 3 sub -2 back to 1950 with 2023 progged by GEFS to become only the 4th:

OTOH, these MJO progs for late Dec suggesting weak left side MJO for then and extending well into Jan and when also considering El Niño and the weak SPV progs, tell me that the possibility of a cold E US overall and even moreso in the SE US in particular is there based on many analogs that I’ve posted showing MJO/E US temps: these end Dec moving slowly in weak 8 and likely would then go slowly into weak 1 followed by weak 2, a recipe during El Niño based on analogs for a multi week dominated cold E US

Although not quite as weak in late Dec as some of the runs, this latest run has the weakest in the 1st half of Jan with a total of ~38% of members with a major SSW 12/23-1/16! ~20 go sub -10, ~16 go sub -15 and ~10 go to sub -20 (extremely weak). There are even 4 that go sub -25, among the weakest on record. These #s are all the highest yet. To compare, the major SSW of 2/17/23 went down to -13, which itself was quite notable.

The cyclonicwx 3.4 rose similarly from +2.01 to +2.12. Latest cyclonicwx: 1+2: +2.10 (down from +2.3) 3: +2.07 (up from +2.05) 3.4: +2.12 (up from +2.01) 4: +1.91 (up from+1.75) Thus this is about as flat/basin-wide as you can get.

The new WCS (for 11/29) had a big daily jump to +2.10 from +1.99 the prior day. So, most likely cyclonicwx will have a gain today.

The model consensus progs have strengthened the MJO in both the MC and WP since yesterday: Though not at all a reliable model, the CFS is fairly similar to where the GEFS and EPS are on Dec 14th, the end of their runs. Note where the CFS then goes, into weak 8/1/2 in late Dec (including inside COD), which tends to favor a cool to cold E US, especially SE US:

Note that in case you didn’t know, 1965-6 had a very early major SSW (in early to mid Dec) per this: https://en.m.wikipedia.org/wiki/Sudden_stratospheric_warming

The 11/28 EPS actually has ~35 members of 101 (35%) having a major SSW (10 mb 60N zonal mean wind going below 0 m/s) during late Dec or early Jan with 18 members (18%) getting below -10 m/s. I consider that to be more than a low probability, especially with that strong of a signal 3.5-6.5 weeks out. Longterm climo says that there’s only a 20-25% chance of a major SSW from Nov through early Jan. So, the latest EPS showing a 35% chance for just that 3 week period is WAY above the climo chance for just that period.

The week 12/25-1/1 is a transition from a bit warmer than normal the week before to the cold 1/1-8. So, changeable, leaning cold last few days of 2023. Similar El Niño favored precip pattern of near to wetter than normal with wettest near SE coast and no dry suggested. With MJO then progged to be in phases 8/1, 12/25-1/1 will have the chance to be a cold week, too, along with a shot at wintry precip.

The Euro Weeklies have been showing cold in the SE US during the first week of January ever since they reached that far. This cold is being supported well by a progged weak to very weak SPV, progs for a weak to moderate slow moving MJO phase 1 then (typically cold in Jan in SE), prog for a textbook +PNA/Aleutian Low (supported by phase 1 MJO combined with Nino climo), and general winter Nino climo. Today’s is about the coldest yet and is quite notable being that it’s a 101 member ensemble out 6 weeks: Combine the cold with this… Euro Weeklies precip anomaly probabilities for 1/1-8: Gulf/Miller A potential? This is a signature for that potential. Shoutout to @pcbjramong others regarding this. Just about all of the SE US is favored to be either NN or AN (no dry), which is significant for a cold period since they can easily be dry. This is where El Niño would likely be helping with moist, cold split flow:

Today’s Euro Weeklies precip. anomalies probabilities for 1/1-8: Miller A/nor’easter potential? Just about all of the E US is favored to be either NN or AN (no dry), which is significant for a cold period since they can easily be dry. This is where El Niño would likely be helping with split flow:

Today’s Euro Weeklies: 1. H5: Best run yet in the E US for the first week of Jan, especially as regards H5 with a textbook +PNA/Aleutian Low (most of E US BN at 2m): 2. SPV: Weakest run yet for late Dec/early Jan with a whopping ~35% of members showing a major SSW (vs prior highest of ~30% yesterday) and ~18% of members going below -10 m/s (vs prior highest of ~12% both yesterday and one from last week), indicative of a notable major SSW. These are quite high %s for something showing up 3.5-6.5 weeks away! 35% is much above the longterm chance of 20-25% for a major SSW occuring by Jan 13: