GaWx

If that is actually all snowfall and not sleet or ZR, the 1.5-2” down here at SAV on that run would be the 2nd heaviest early Dec snow on record with only Dec 6th of 1740’s 4-5” exceeding it.

Today’s Euro Weeklies mean is similar with the weak Dec SPV of yesterday’s run. The EPS mean 60N wind for Dec 7-31 as a whole is at only ~2/3 of the longterm climo mean for Dec. 7-31: li

Cyclonicwx’s Nino temps: 11/24 update 1+2: +2.05 3: +2.40 3.4: +2.20 (vs +2.16 yesterday and WCS’ +2.19) 4: +1.48

The latest WCS Nino 3.4 OISST rose from +2.12 two days ago to +2.15 yesterday to +2.19 today (as of 11/22). So, although it appeared warming was slowing some yesterday, it is still steadily warming. So, look for a further warming on today’s cyclonicwx graph, too. So, as we approach +2.20 on OISST, one might wonder if that, alone, makes an unrounded +2.00+ ONI peak likely. My opinion is that that, alone, doesn’t. On the dailies, a +2.40ish daily peak is probably going to be needed based loosely on the past. Even on the weeklies, a +2.3 is probably going to be needed based on the last 5 Nino’s. We do have a good shot at a +2.10 week in the next release. So, to get the +2.00 peak ONI, the dailies likely need to warm another 0.20 or so. With today’s warming, we’re likely going to have a +1.80 or so ONI peak at the minimum. The WCS daily PDO major rise of the last two days took a break with it at -0.86 vs -0.84 yesterday.

NOAA OHC time series update (5N to 5S)(1991-2020 base):

Todays Euro Weeklies SPV strength update was to be a big test because of yesterday’s huge move weaker. The result is that todays not only upheld yesterday’s update, it went further throughout Dec! As of just three runs ago, the Weeklies had a strong SPV for Dec as a whole. Now it has just about the exact opposite! The EPS mean drops below climo on Dec 4th. This compares to 12/25 just three runs ago! And not that a major SSW is required for a weak SPV to result in a -AO/-NAO to become dominant, but today’s update based on the individual members implies a 20% chance of a major SSW just through the first week of January, which is about the highest yet for any run. Keep in mind that the vast majority of major SSWs occur mid Jan or later and that well under 20% of winters through Jan 7th have had a major SSW: Today’s Euro run: weak SPV dominates Dec: Euro from just 3 days ago: strong SPV dominates Dec:

The latest for Nino 3.4 is +2.16 per cyclonicwx and +2.15 per WCS. The warming is slowing for now. We’re still a good ways from a super (one trimonth of +2.00+ is my definition). A highest daily max of ~+2.40+ would probably be needed to allow for a super, which may never be reached obviously:

Why doesn’t Jan take it all the way and require five trimonthlies for strength, too? If he’s/she’s going to be 100% consistent, that’s what Jan would need to do. Why stop at just three? Is Jan requiring only three to make sure 1982-3 is classified as super? It only had three trimonthlies at +2.00+ unrounded: SON 1982 28.50 1.97 OND 1982 28.70 2.18 NDJ 1982 28.76 2.23 DJF 1983 28.79 2.18 JFM 1983 28.75 1.92 I think Jan’s too strict. I still count 1972-3 as super as the majority of posts explicitly addressing it here have done to the best of my memory despite it having had only two trimonthlies and only two months of +2.00+. Its trimonthly peak was +2.12. Different strokes for different folks though consistency is of utmost importance to me. For those who go by NOAA, they’ve already called the current event “strong” after just one trimonth of +1.50+. Regardless, I feel that for the best measure of relative effects vs prior events, RONI is a better measure and it is only in low end moderate so far with +1.05 for ASO. It will rise but it is questionable whether or not it will reach strong (+1.50+ unrounded RONI) per this: https://www.cpc.ncep.noaa.gov/data/indices/RONI.ascii.txt There are so many different ways to look at this that it could drive us crazy! But for assessing @snowman19’s prediction, I’ll require only ONE UNROUNDED trimonthly of ERSST of +2.00+. To require more would not be fair imho. Hardly anyone else here other than @George001has expected even just one trimonthly of +2.00+. Even my own latest prediction is for a trimonthly peak of only +1.7 to +1.9 (meaning the highest and not requiring more than one within that).

I'll call this one super if the UNROUNDED ERSST trimonthly peak is +2.00+. No hidden agenda. So, if it is only +1.99, I'll call it just strong, even though the ONI table would show it as +2.0. If it comes in at +2.01, I'll consider it super. I've not seen a requirement for +2.1C. I've always seen +2.0 as the key threshold just like +1.50 for strong (NOAA just called the current Nino strong per @bluewave) and +1.00 for moderate. But to each their own. The current Nino was for ERSST unrounded at +1.54 for ASO (the only trimonth at +1.50+) per the following link of unrounded trimonthlies and it has already been classified as strong by NOAA: https://www.cpc.ncep.noaa.gov/data/indices/oni.ascii.txt

Meanwhile, the WCS daily PDO just rose by a large amount for the 2nd straight day. It has risen a whopping 0.35 in just 48 hours (0.17 yesterday and 0.18 two days ago):

On the linked table, the minimum to officially be counted by NOAA as El Niño (red) or La Niña (blue) is, indeed, 5 consecutive trimonths of 0.5+/-0.5- (we all agree on this): https://origin.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ONI_v5.php For El Niño strength above weak, I’ve always gone by the peak strength of the trimonthlies without requiring multiples. Example: 1972. If that required 5 months of +2+ ERSST, it would be only strong rather than super because only Nov and Dec were +2+ per this table: https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/detrend.nino34.ascii.txt But I’ve always seen it classified as super here and elsewhere.

At least there appears to be a decent -AO. Also, the ante is upped, especially as we head into Jan, by the potential much weaker SPV that’s showing on this run.

When combined with the Dec 25-Jan 1 map that I’ve seen, that means the near two week long period of 12/25-1/6 centers the coldest anomalies over land in the entire NHem in the E US. Keeping in mind that there’s often strong cold air during winter in some mid latitude area at any time, this implies the real possibility of a couple of weeks of that kind of thing in the E US then.

I wish there were an exclamatory reaction emoji! I mean this is by a large margin the biggest weakening on the Euro Weeklies from one day to the next since I started following this on a daily basis. Just two days ago (11/19 run) the ens mean was delayed til 12/25 to go below climo, which was vs ~12/1 on the 11/1 run. I mean major can kicking! Yesterday it moved from 12/25 back to 12/19 a pretty significant weakening on its own. But today takes the cake with it moving from 12/19 to 12/5! The ens mean gets to as low as 21 m/s vs high 20s to 30 the last few runs. The implied chance for an actual major SSW just shot up from under 5% two runs ago to the 15-20% region today.

How would this H5 change once the MJO winds around to 8/1/2, which is being suggested for midmonth on?

Latest TAO (for 11/16-20 averaged): vs prior map warming in 3.4, especially S of equator; warmest SST >31C 170W-180 just S of equator: strongest of WWB now moved E to 150-155W:

WCS daily updates: -Latest Nino 3.4 is still warming steadily and rose from +2.07 to +2.12 -The PDO rose sharply from ~-1.19 to -1.01. That’s the largest daily rise since ~10/17. Cyclonicwx: -1+2: +1.84 -3: +2.30 -3.4 rose from +2.05 to +2.13, another sharp rise! It’s now about same as the +2.12 of WCS. -4: +1.47

There have been only 6 sub -0.25 NAO winters during the last 44 (only 14%)…so this goes back to well before the internet and first online wx BB/before many here were born! So, the frequency of even just moderate -NAO winters has been way down during winter for decades. This is in deep contrast to: -a much higher frequency of -NAO winters than 14% during the late 1950s through 1970s -a big increase in -NAO summers during the last 30 or so years

Regarding the SER: a very knowledgeable and smart met whom I communicate with at times and who I feel is objective without strong political influences and who is neither a winter weenie nor an anti-weenie has been following the avg SSTa for an area of the tropical Pacific N of Australia (120-160E, 15N to 15S) (within the MC) for years that he feels is partially correlated to increased frequency/amp during winter of MC MJO phases, increased forcing from the MC even when the MJO isn’t in the MC, and an increased avg SER strength/La Ninalike pattern. During the prior few years, it had been near record warmth. However, during Aug-Oct of 2023, it was quite a bit cooler than that for recent years. I’ve posted about this in here. We’ll see how it ends up in Nov as it may have warmed a good bit. Regardless, my hope is that the strong El Niño keeps the SER weak this winter no matter how warm this area ends up this winter.

As per what’s in the top image, Phase 8 has on average been the coldest in NDJ in the E US with phases 1 and 7 next coldest. As far as I know (I realize this has been debated), no lag time has to be added as this is what is experienced on average during each phase from what I understand. And to add based on my own analyses, I found that weaker amplitudes of each phase at least during El Niño averaged colder than stronger versions. With phase 6 averaging the warmest, a 6-7-8 isn’t usually all that cold in Dec because of the warm 6 unless the time spent in 6 is short enough. I’d prefer a 7-8-1. That’s why I’d rather not see it too warm in Nino 4 and want to see warmth move well east into central 3.4. Also, when Jan/Feb comes, phase 7 becomes mild and phase 2 cools off and even phase 3 cools off by Feb (see 2nd image). NDJ DJF:

From the hints that I’ve been seeing, I don’t think the E US is going to be affected by a consistent single pattern in December, which I realize isn’t unusual. I’m leaning toward a first half with temps averaging AN and a 2nd half with much of the area averaging BN, especially MidAtlantic south. If this were to verify, we’d be looking at a largely NN Dec as a whole in much of the E US, especially MidAtlantic south, as opposed to a mild Dec.

For the perspective vs the rest of the globe, you can see how cold at 2m is the E and C US as a whole, especially the SE US, on today’s Euro Weekly for 12/25-1/1: pretty much as cold as the coldest anomaly for any large land area as the vast majority outside of the lower 48, Alaska, and Greenland are in pink and only a few small land areas are in blue. So, this map suggests the E US could very well be headed toward another cold holiday period thanks to an El Niño/left side MJO favored +PNA.

Here we go: coldest 500 mb and 2m Euro Weeklies maps for 12/25-1/1 so far with a W Canadian block and E US trough (+PNA)/Aleutian trough: H5: 2m:

I want to make sure I’m looking at this right. Are those 500 mb height anomalies? If not, what are the reds and the blues? Edit: I got the answer. They’re 300 mb ht anomalies.

Indeed, here’s the map that Roundy showed. Assuming I’m interpreting this correctly, it appears to have the strong Canadian block (in red) that he mentioned, which is in W and C Canada and includes the NW US. That is a strong +PNA block along with an Aleutian low to its west (in blue). The accompanying +PNA trough dips down into the E and EC US (blue). This looks like a strong +PNA block for 12/28/23. This would normally be quite a cold pattern for the E US and probably with the strongest cold anomalies in the SE US. This also seems to show a modest -NAO with some red over Iceland/E Greenland and blue to the south. (This cold pattern in late Dec would be consistent with the cold E US pattern being suggested by recent MJO model forecasts for mid Dec due to weak phase 8.)