GaWx

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:

If your educated guess were to verify and if especially the DJ MEI were to be ~+1.1 to +1.2, that would be just about as good a scenario as one should want to see as regards cold winter chances for the bulk of the E US based on past MEIs. The ERSST Nino 3.4 SSTa is going to come in ~+1.83 for ON vs +1.63 in SO. So, a rise of 0.2. That should support an MEI rise. But if the SO SOI goes directly into the SO MEI calc, it in isolation would not be supportive of an MEI rise because in ON it is aiming for ~-7.5 vs SO’s ~-10. Hopefully, it wouldn’t have much impact as the SOI rise is small.

Of course, the sweet spot will vary depending on the region. I already analyzed the MEI for the SE US including TN: the 10 coldest El Niño winters back to 1951-2 were 1957-8, 1963-4, 1965-6, 1968-9, 1969-70, 1976-7, 1977-8, 2002-3, 2009-10, and 2014-5. Per Webb’s table these were the rounded DJ MEIs: +1.5, +0.9, +1.3, +1.2, +0.8, +0.8, +0.7, +1.0, +1.1, and +0.5. So, range of +0.5 to +1.5 for the DJ MEI with a mean of +0.95 and a median of +0.95. So, DJ MEI sweet spot near +1.0 for the 10 coldest in the SE. The 6 coldest were 1957-8, 1963-4, 1969-70, 1976-7, 1977-8, and 2009-10. DJ MEIs for these 6: +1.5, +0.9, +0.8, +0.8, +0.7, and +1.1. So, range of +0.7 to +1.5 with mean of +1.0 and median of +0.85. So, I’ll be rooting for a significant rise in the next three bimonths from SO’s 0.26. I’d like to see a rise of +0.2+ back to +0.5+ in ON. Was 2023’s drop of 0.33 from AS to SO the largest back to 1948 for El Nino? Actually, no as 1986 dropped slightly more (0.40) before it rebounded 0.50 from SO to ND, which I’d love to see. Webb’s 1948-2019 MEI: https://www.webberweather.com/multivariate-enso-index.html

No, dropped a little from +1.98 to +1.97.

WCS updates: -Nino 3.4 dropped very slightly to +1.97 from +1.98 -PDO dropped from -0.84 to -0.93.

OHC has again been readjusted warmer but also was just extended out 5 more days: the result is by far the warmest this Nino with ~+1.6 as of Nov 22 and is still suggesting more sharp rises! Those very warm TAO maps are finally being reflected here. It looks like Nov will easily end up the new warmest month for this event so far barring something unforeseen:

In addition to what the EPS has been showing, possibilities are there for SSW late Dec-early Jan per 11/27 extended GEFS, too:

I like the every six hours frequency. However, that’s CDAS based, which is quite cold biased.

This is easily the strongest cold signal for the first week of January in the E US of any Euro Weekly run that I’ve seen and as strong a cold signal as for any land area on the globe for then. Keep in mind this is way out in week 6, when it is hard to have a strong signal away from normal in an ensemble mean. This timeframe is consistent with an MJO prog favoring cold in the E US. Per @griteaterposted MJO chart the prog is for a slow moving fairly weak (just outside the COD) phase one then, which tends to favor cold in the E US, especially during El Niños: Looking further out on griteater’s MJO prog, the week after this is progged to continue to move slowly in weak phase 1 and then entering weak phase 2, which would favor another cold week Jan 8-15. The last time the first half of Jan was cold dominated in the E US was in 2018. Though not El Niño, it was mainly in a moderate MJO phase 2:

Even with it that large, it is imo likely mainly due to day to day flux. Even the drop of 0.17 in 5 days isn’t too far out of line from a correction considering it had risen ~0.5 in just 10 days. So, it has given 1/3 of that back. Now, if it were to drop too much more from here, I might have second thoughts.

The cyclonicwx Nino 3.4 dropped by a similar amount, from +2.15 to +2.03, the biggest daily drop in a very long time:

Meanwhile, WCS just reported the largest daily drop in Nino 3.4 in two months with a drop from +2.10 to +1.98! That’s the coolest on WCS since Nov 16th and certainly unexpected by me: The daily WCS PDO dropped to -0.84 from -0.77.

Yeah, I was using unrounded. For rounded, what @griteater said makes perfect sense.

I agree with your general ideas. Per ERSST, Oct was +1.66 and Nov is likely going to be in the general vicinity of +2.0. So, for OND to come in +2.0+, Dec would probably need to come in near +2.35, likely a tough task. The better chance may be with NDJ (I’m guessing you agree) with its first month near +2.0. For that, Dec could come in, say, ~+2.1 and Jan, say, ~+1.9 or, say, Dec ~+2.2 and Jan ~+1.8 and a +2.0 ONI is reached either way.

As expected, today’s weekly OISST based NOAA update (for last calendar week) for Nino 3.4 came in at +2.1, an increase from the prior week’s +1.9. Also, for the first time since way back in early Feb, the weekly Nino 3.4 anomaly came in warmer than that for Nino 1+2, which remained at +2.0. Today’s weekly NOAA update: Nino 1+2: +2.0 (steady) Nino 3: +2.3 (up from +2.1) Nino 3.4: +2.1 (up from +1.9) Nino 4: +1.5 (steady) https://www.cpc.ncep.noaa.gov/data/indices/wksst9120.for

No worries, Mitch. If you decide to delete your two recent posts, I’ll also delete my replies to clear the thread.

I know. I already posted the 11/26 update here as it updates by late afternoon (before night). So, the next update (11/27) will be by late afternoon today:

The OHC is still being adjusted upward for the same timeframe and is now showing a new high on this graph for this event of ~+1.40 with further ongoing sharp rises being suggested. Keeping in mind reporting lag as this particular graph is updated only through ~10 days ago (midmonth instead of late month), Nov has a good shot to exceed June as the warmest month of this Nino so far in the monthly table. This is for 5N to 5S down to 300m and uses a 1991-2020 base:

The 11/1-18 Euro Weeklies runs were making me think a weaker than normal Dec SPV model bias quite possibly was in play due to major can kicking. The date of the SPV going below climo slipped from ~12/1 to 12/25 and thus it stayed a month+ out/like a mirage. However, the last 8 runs have come all the way back along with extending into early Jan with the last 5 runs being very impressive with today’s having the most major SSW members (30%). Thus, I no longer think a model bias is in play. Furthermore, there’s modest support on the extended GEFS. And don’t forget that the CFS fwiw is supporting a weak SPV this winter. So, I now fully expect a weak SPV will at least dominate Dec (with or without a major SSW) and may very well go into Jan. Now if we actually get a major SSW late in Dec, it could rebound within a few weeks as they sometimes do.

It looks great once again on the EPS for those who want a weak SPV. Similar to yesterday, the EPS mean goes weaker than climo 12/3 and is well below climo 12/7-end of run (1/10). Not that it is necessary, but this run implies the highest % of members yet with a major SSW (between 12/24 and ~1/11), 30%, which beats the 25% on yesterday’s run. The climo % chance of a major SSW by Jan 11th is only ~20-25%. More specifically, this run has 12% of its members with quite a potent major SSW (dip to <-10), which is tied with the 11/25 run for the highest of any run yet!