GaWx

Model consensus 12/25 fwiw threat of rain much of SE and mainly warmer than normal with SW upper flow. I say fwiw because it still being 8 days out means lots of uncertainty/model inaccuracy.

Down to 996 mb inland over N FL (Cross City). Gainesville 998 mb with ~5” of rainfall with still heavy showers in the area! That 998 mb ~ties their record low for Dec. It rained here all night. Edit: power out here since 9:45AM due to persistent gusty winds of ~40 mph. Power returned just over an hour later. Winds now picking up perhaps a little higher on backside of low with cold air advection. Will have to watch for potential additional outage. KSAV 11AM SLP 29.49”/999 mb, possibly near to bottoming out Record low Dec SLP ~29.35”/994 mb Edit: KSAV 2PM SLP 29.41”/996 mb

I agree. Looking back at the 2/16/23 major SSW (when zonal wind went <0), let’s see how long it took for the bulk of the ensemble members to get clued in. The runs from 2/1/23, 15 days out, still had little clue as a mere 8 of some 60 or so total ens members (only 13%) had a major SSW (though the GFS was strongly hinting at it similar to how a couple of recent GFS runs have already done): Not til the 2/3/23 runs (13 days out) did the ensembles really seem to be much more onto it: So, looking ahead to the potential one for early Jan, we’re talking perhaps near Jan 1-3. Jan 1st is still 15 days out while Jan 3rd is 17 days out. If anything, the ensembles are and have been showing a somewhat higher % of members in very early Jan with a major SSW this time than were being shown 15 days prior to the 2/16/23 event. This tells me that we’re still likely ~3-5 days from put up or shut up time. So, I’m thinking we probably have til ~Wed-Fri of this week to finally consistently start seeing a forecasted notable 60N 10 mb wind collapse from, say, near half the members if there really is going to be one in the first few days of 2024. Along with that, perhaps we’d see some GFS runs with majors. If any actual event were to instead not be coming til, say, 1/5-7, we’d then probably have still another week or so (say ~12/25) til put up or shut up time on the models.

My area has been getting pretty heavy rain the last 1/2 hour or so. Meanwhile, @pcbjr’s abode in FL (Gainesville/Hogtown) has been hit with heavy rain for several hours. Hopefully, flooding isn’t bad there.

Although the 0Z 12/16 extended GEFS isn’t quite as active as yesterday’s run overall (7 members/23% vs 8 members/26%), it actually is more active earlier as it has a respectable 5 members (16%) with a major SSW just within the 5 days 12/30-1/3. Yesterday’s had only 3 during 12/30-1/3. The day before had only two for then I believe. Even the big 12/11 run had no more than about the same for then. So, look out for the possibility of one within a few days of New Year’s, which as has been mentioned is a climo favored period for QBO east.

New Euro Weeklies NN to BN temperatures SE every week through 1/29 with FL BN every week! Precip AN favored every week nearer to coast with NN far inland and no dry areas@pcbjr

What he said to a good extent (though not 100% back as weak near New Yr): ~17% major 12/30-1/6 and back up to ~50% full run vs ~33% yest. Sig weaker mid to late Jan. Extreme ~13% vs 7-8% last 2 days and ~17% 3 runs ago. Also, back below red line most of 12/28-1/5!

Further to the above 0Z GFS image, the 10 mb at 60N winds (orange) gets down to <8 m/s at end with more drop likely past this. Despite EPS/GEFS runs consistently showing a notable % of members with a major SSW in early Jan, the level of weakness on this GFS is still somewhat of an outlier considering that run’s GEFS mean is at 20 m/s. However, should there really be a major SSW coming near then or soon after, model consensus would be showing this type of thing more often as it gets closer. We’ll know more and more as the coming days of runs are seen:

1. This 0Z 12/16 GFS 384 appears to be approaching a major SSW 12/31-1/1 with the SPV down to 65N and a huge high centered over N Canada/AK: 2. The 0Z 12/15 GEFS has a similar % of major SSW members to 12/14 for the full run. However, the mean is a bit weaker 1/2-11 due to a sig increase in them 1/2-6 with a whopping 7 majors (23%) just during that period vs only 2 (6%) in the 12/14 run for then. The 23% for 1/2-6 is actually the same as was the case for 1/2-6 on the 12/11 run that had 48% for its full run. The total is 8 (26%) 12/15 vs 7 (23%) 12/14.

Other than week 2 having 2-3 F AN temps in NW portions, the Euro Weeklies have NN to BN temps in the SE through Jan 29th. And this is with most members having no major SSW. Imagine what could happen in mid and especially late Jan if there is one.

They could since we’re still far enough out in time for that to occur. But by a week from today, the models will know a lot more based on the past. So, say by the 12/21-2 runs, if the runs don’t jump back quite a bit in the weaker direction, I’d then significantly reduce the chances in my mind for an early Jan major SSW. I like to give updates, especially those showing significant changes, whether or not it is what I want to see. I don’t want to come across as one who posts either mainly about what I want to happen nor the opposite. I want to come across as one trying to be as objective as possible for credibility reasons.

I assume you meant to say they shouldn’t. I see no problem with every day for both as they help for following trends. I like to see daily updates. Now if they ran, say, 4 times a day, I’d agree with you.

Neither last night’s extended GEFS (12/14 run) nor today’s Euro Weeklies (12/15 run) was what I wanted to see as they both suggest a sharp decrease vs earlier runs in the chance for a major SSW anytime soon: 1. Extended GEFS: % of members with major SSW 12/11 run: 48 12/12 run: 32 12/13 run: 29 12/14 run: 23 2. Euro Weeklies: After many days showing 45-60%+ of members with a major SSW, today’s suddenly plunged to only ~33%. Yesterday’s was ~50% with a whopping ~17% for 12/28-1/2, alone. Today’s has only 3% for 12/28-1/2! Today’s has 17% for 12/28-1/12 and only 21% through 1/17. The extreme major SSW (sub -15) members stayed ~same with 7% vs 8% yesterday though that was ~17% two runs ago:

But likely only 8th warmest RONI peak and 9th or 10th warmest MEI peak at best (could turn out to be as low as 15th) out of 25 El Niños since 1950 when all is said and done. So, based on RONI and MEI, whereas we’re in a robust El Niño, it isn’t impressive historically. Meanwhile, OISST 3.4 jumped back up to +2.02 from +1.92 on cyclonicwx. It keeps going up and down in this area without any real direction of late.

That’s similar to what I found for the DJ MEI range most correlated to cool to cold E US winters. I don’t want the MEI to be either too strong or too weak. The MEI sweet spot seems to be in the general vicinity of +1.0 for DJ. Thus, I see this adjustment up of ON to +0.8 as good news as far as better prospects for E US BN temps are concerned. Looking at the 25 El Niños since 1951-2, the average change from the ON MEI to DJ MEI was near 0. For 85-90% of these, the absolute value of the change was 0.3 or less. So, that tells me that there’s a high chance that DJ will end up between +0.5 and +1.1. The 10 coldest winters (at least mid-Atlantic south) averaged between +0.9 and +1.0 in ON. The ON for both 1977 and 2002 was the same as 2023’s +0.8. 1963’s ON was very close with it at +0.9. OTOH, sometimes with similar ON MEI, the winter turned out to be mild like 1951-2 (though its DJ fell to only +0.3) and 1994-5. Regardless, for the best shot at cold, the +0.8 of ON is good to see. https://www.webberweather.com/multivariate-enso-index.html

Today’s run has the weakest SPV period starting the earliest in many runs and that period starts only 14 days out, the earliest in any run yet. I count ~17% of members with a major SSW just from 12/28 through 1/2, alone! Moving up like that is a pretty big deal. It earlier looked like @40/70 Benchmarkgetting a major SSW in the first of his two weeks was looking very highly unlikely, but this is telling me the latter half of his first week is now back to being very much in the game:

Dec low SLP records could be challenged in GA, SC, and NC per this:

Whereas the CFS GLAAM forecast is still solidly positive, it has come down a good bit from what was forecasted two days earlier with +1+ instead of +2+ at early Jan peak

Regarding cold periods during DJF in the E US, a large portion of them occurred during weak MJO per this: https://scholarsarchive.library.albany.edu/cgi/viewcontent.cgi?article=1007&context=honorscollege_daes

Note that the coldest and snowiest part of the month was Jan 15-31, when the MJO was weak (near or inside the circle). Jan 1-14 averaged near normal temps whereas Jan 15-31 averaged B to MB. This was similar to the case in the SE US, where Jan 1-14 averaged A with temps before being MB Jan 15-31 along with above average snow.

From Judah Cohen’s blog: “A larger PV disruption is more likely in early January that has the potential to reverse the overall mild pattern for the NH to a much colder one. Hard to provide details just yet and I expect a lot of volatility in the forecasts so buckle up.” “It is of my opinion, much of the winter will likely hinge on the nature of this SSW that is predicted to begin the last week of December.” https://www.aer.com/science-research/climate-weather/arctic-oscillation/ ————————- Interesting update from Judah! Keep in mind that major SSWs are often though not always accompanied by mildness in the E US before, during, and afterward prior to it later getting colder as their influence moves down into the troposphere and often results in a -AO/-NAO to then dominate. It often takes 1-3 weeks (avg ~2 weeks) for them to get deep down into the troposphere. It can of course already be cold when they occur, but that would obviously be due to other factors like a favorable MJO, for example.

Today’s 0Z extended GEFS mean, like recent runs, suggests a significant weakening of the SPV and warming of the Arctic in early Jan. But will there actually be a major SSW/reversal of 60N winds? That’s the big question:

Today’s Euro Weeklies are about as weak as any run yet for the last few days of Dec/early Jan. Total major SSWs are ~~50%. The highest concentration of major SSWs occur Jan 2-9 (~25% of members), which is supported by E QBO climo. (The extreme SSWs throughout Jan increased with ~17% total sub -15, ~15% sub -20, 5% sub -25, and 2% sub -30.): 10 mb temp anoms/hts 1/1-8: Also, Jan 8-15 cooled back almost to as cold as the run from 3 days ago. But no football spiking from me!

Yeah, this trend isn’t at all what I wanted to see. This means that the NOAA PDO is quite possibly back down to ~~-2.0. My hope is still for a sharp enough reversal soon to allow for a JF PDO to average >-1 in the NOAA table, a doable but unfortunately very tall task as of now. But regardless of the PDO, the good news from an E US cold lovers standpoint is always having the major SSW wild card possibility to shake things up drastically via -AO/-NAO blocking in Jan and/or Feb as it often means a major atmospheric reset. All major SSWs since 1958 during El Niño have had a 3+ week long period of cold domination after 1-3 weeks following them as I’ve posted about. 60% of El Niño winters have had a major SSW. Also, QBO E have had more than QBO W. The best shot at a major SSW during QBO E per analogs is very late Dec to early Jan as per@40/70 Benchmarkand SSW history. If we can get that combined with weak MJO, I’d be pretty excited about potential for E US cold in a good portion of Jan and/or Feb.

1. That’s about to drop to ~+1.9 based on WCS dropping from +2.0 to +1.89 in today’s update. 2. The WCS PDO has been falling sharply in recent days and is -1.35 in the latest, the lowest in two months (NOAA may be back down to ~~-2):