GaWx

New Euro Weekly 2m temps for Jan 6-12 (see image below) is by a good margin the coldest yet and is the coldest Euro Weeklies map covering a 7 day period and still over a week out I can ever recall seeing for the E US: the 3rd shading of blue is 3-6 C/5.4-10.8F BN, which covers just about everywhere in and near the E including 200-300 miles offshore the E coast. That means the bulk of the E US is 7-10 BN! There’s even a tiny area of 3rd shade (-5.5F) in Cuba! The coldest is in W VA, where for the first time a tiny bit of the 4th shade is showing (~11F BN)! This map is easily the coldest on the entire globe for that week and beyond. Also, the subsequent week is cold. Here’s Jan 6-12:

New Euro Weekly 2m temps for Jan 6-12 (see image below) is by a good margin the coldest yet and is the coldest Euro Weeklies map covering a 7 day period and still over a week out I can ever recall seeing for the SE: the 3rd shading of blue is 3-6 C/5.4-10.8F BN, which covers everywhere in and near the SE including 200-250 miles offshore along the SE coast. The bulk of the SE is 7-9 BN! There’s even a tiny spot of 3rd shade in Cuba (~5.5 F BN)! That’s very hard to accomplish. The coldest is in W VA, where for the first time a tiny bit of the 4th shade is showing (~11F BN)! This map is easily the coldest on the entire globe for that week and beyond. Also, the subsequent week is cold. 1/6-12 Precip map is wettest for that period, yet (NN to AN everywhere)! It shows Miller A potential. That equates to ~1-1.25” in most areas, a lot of qpf for such a cold period since they’re often dry:

A quick look at all 3 12Z ensemble run members continues to show a decent % with wintry precip (flurries/T or more) in FL. I counted on the EPS 15 of 50 (30%) in FL! On the relatively conservative EPS this far out (7 days+) that is very notable and gets me excited for a shot at least flurries here. Haven’t had even a T of any kind of wintry here in 7 years.

All 3 12Z ensemble means are very cold in the SE late. It’s almost a certainty that an overall cold first half of Jan is on the way for the SE with the coldest first half by far since 2018 (all others since NN to AN). It will very likely end up colder in the SE overall than 2014 and 2015, which weren’t that cold in the deep SE. So, it looks likely that the first halves of Jan in 2011, 2018, and 2025 will be the coldest 3 of the last 15 for the SE overall, all 3 being La Niña. Both 2011 and 2018 had one major winter storm in the first half of Jan affecting parts of the SE: -1/9-10/11 was big in much of the well inland SE including Atlanta, where it had a very large impact and lead to closings much of that week -1/3/18 historic SE coastal winter storm A notable winter event or two is likely in the first half of Jan 2025. How notable and where nobody knows.

The updated bc GEFS/EPS are still looking favorable for cold (it’s hard to be in a better position than these weak left sided tracks): Yesterday’s extended bc EPS *fwiw* suggests no strong MC anytime in Jan:

That would make 2024-5 a significantly stronger La Niña than 2008-9 on a relative basis to surrounding tropical waters’ anomalies considering that RONI and ONI were very close in 2008-9 vs 0.5 to 0.6 apart now.

If this daily RONI chart is pretty accurate, OND RONI would end up near or slightly cooler than -1.0. That would already give 2024-5 a borderline moderate/weak La Niña peak at the very least on a relative to surrounding global tropical waters basis. My guess for official OND RONI is at least down to -0.95. When combined with other factors including the SOI, I consider that we’re in moderate La Niña for all practical purposes although not officially (not ONI-wise).

The 0Z EPS mean is much colder than the 12Z and is the coldest of any yet. For example, much of the Carolinas are ~9F BN over the 9 days Jan 2-10! That long of a period is categorized unofficially as cold for an ensemble mean. The E US easily has the coldest anomalies of anywhere on the globe for Jan 2-10 overall! Thus, I’ll be surprised if tomorrow’s weeklies aren’t the coldest yet for the week of 1/6–12. The southern extent of the measurable snow mean is about the furthest south yet of any EPS run with it reaching much of the Gulf/SE coasts keeping in mind that the EPS is the most conservative of the 3 major ensembles: The typically more liberal GEFS (0Z) has the measurable down to @pcbjr’s abode in Hogtown! This is about as far south as I can recall even the GEFS mean ever going in the FL peninsula:

1. Thanks. But operationals are almost always jumpy at 240+. So, I put little importance on operationals days 10+, when I prefer ensemble means. 2. So, looking at 12Z Euro/GFS/CMC ens means, the trof is ~80W/near our longitude. 3. Would it be too dry for the SE to get a synoptic scale winter storm with the mean trof near 80W? I’d say yes in many cases, especially when there’s just the N stream keeping it dry. I’d then prefer it be ~90W. However, an often hard to prog (more than a few days out on models) short-wave induced split flow underneath the N stream would be a way to make it moist while the N stream to the north keeps the cold air in place at the sfc. 4. Here are 9 examples of moist split flow just in advance of SE winter storms even with the N trof even further east in all but one case: 12/8/18: (El Niño) N trof 72W but WSW flow SE 12/8/17: (La Nina) N trof 85W but SW flow SE 1/21/16: (El Niño) N trof 70W but WSW flow SE 2/25/15: (El Niño) N trof 77W but WSW flow SE 1/9/11: (La Nina) N trof 70W but incoming SW flow underneath 2/11/10: (El Niño) N trof 65W but incoming WSW to SW flow underneath 1/29/10: (El Niño) N trof 70W but incoming SW flow underneath 2/25/04: (warm neutral) N trof 70W but SW flow SE 1/9/04: (warm neutral) N trof 60W but WSW flow SE 5. Could there be a shortwave induced moist split flow underneath the progged 10-15+ day +PNA induced cold mean E trof coming that can’t yet be seen on ens H5 means? It’s very possible. Would I bet on it? No because we’re in La Nina, when it is more difficult to get a split flow. If this were El Niño with a frequent moist S stream, I’d be more excited. Regardless, sometimes these occur during La Nina like in 2 cases posted above, 12/8/17 and 1/9/11. Also, the progged couple of week long cold dominated period as opposed to just one and done helps. Plus there are obviously other ways to get a winter storm. So, keep hope alive, folks!

Are you talking about the Euro operational trough or the Euro ensemble mean trough? Also, what forecast days/hours are you referring to?

Despite the recent at or near record rapid strengthening of La Niña from Nov to Dec, Jan is likely going to be another BN temps month in much of the E US. If so and with 2 of the 3 winter months BN, this winter would highly likely not be the AN E US winter (+2+ F) many including both of us expected. In that case Feb would have to be an absolute blowtorch just for the slight chance for DJF to average +2+.

This is about the coldest 12 run CFS ens map I can recall ever seeing for the SE for a full week not starting for 2 weeks meaning a very strong cold signal for the start of the period being 2 weeks out: this has 5-6F BN over almost all of the SE! Remember that this is 12 runs of a 4 member ensemble and is actually likely underdone, if anything, due to smoothing. Precip averages 0.25” BN, which for such a cold period is actually decent since strong cold is more often than not dry. That would still be 0.5-1” of qpf for most.

A split flow (more frequent in El Niño) is often the best bet to get significant wintry precip for much of the SE, including the deep SE (see image below for a deep SE modeled example): -Having the N stream to the north of one’s latitude with the trough axis nearby or to the east (it’s actually well to the east in the image below) allows for ample supply of cold at low levels -Having the S stream near or a little south of one’s latitude with its trough axis to the west allows for moist WSW or SW flow bringing the Gulf moisture/warmth above the low level cold A textbook modeled split flow: note the N stream with cold WNW flow well to the north (trough axis to the east) while at same time there’s S stream with moist WSW flow nearby bringing in ample moisture (trough axis to the west). The precip map for this showed snow on the northern fringes in the deep SE: Edit: These are not easy to achieve as one could imagine (delicate setup), probably moreso when not in El Niño. These are often not going to be seen on ensemble means out more than a few days and they often appear for only a short period.

When I start counting more than just a couple of ensemble members with wintry precip in FL (anywhere from T to measurable), it starts to get my attention for especially us deep SE folks where it is pretty rare. I haven’t had even just a T of any kind of wintry precip in nearly 7 years, the longest for this area at least going back 140 years! The latest runs of 2 of the 3 major ensembles all have the largest # of members like that yet this season (not surprising considering how cold they are and the strong hint of multiple cold plunges as opposed to just one and done). -18Z GEFS: 11 of 30 (37%) have it in FL! Prior 3 runs had 5 each. This usually has highest of the 3 ens but 37% is still very impressive! -12Z GEPS: 4 of 20 (20%); 0Z had only 1 and yesterday’s 12Z had none -12Z EPS: 4 of 50 (8%) but 0Z had 7 of 50 (14%); this usually has lowest of the 3 ens. -The bulk of the wintry events are near the end (Jan 8-10) but a couple on the GEPS are as early as Jan 4. @pcbjr

The latest model consensus covering much of the 1st half of Jan suggests a good chance for a +PNA (trended recently from neutral or -PNA), -AO, and -NAO. (The 2nd half of the month, which only the extended ensembles show, is still too far out for reliability.) During non-El Nino DJF back to 1950, these are the 15 non-Nino months with a +PNA (+0.25+), AO (-0.5-), and -NAO (-0.25-) along with E US temps: -2/2013 (weak +PNA/-NAO; +EPO): cool SE/MidATL, NN NE -1/2011: cold -12/2005: cold -1/2004 (weak +PNA/-NAO but -EPO): cold -12/2001 (+EPO): mild -12/2000: cold -12/1995: cold -12/1989: cold -1/1985: cold -2/1968: cold -2/1963: cold -1/1963: cool -1/1960: mild -1/1955 (+EPO): cool -12/1952 (+EPO): cool SE/mild NE So, 11 of these 15 were cold or cool most everywhere. The other 4: -2/2013: +PNA and -NAO weak and +EPO -12/2001: +EPO -1/1960: can’t explain -12/1952: +EPO So, if we end up with the full Jan averaging +PNA/-AO/-NAO and considering the favorable MJO for at least the 1st half, the odds would be high that the only index standing in the way of a cool to cold E US Jan would be a +EPO. Current consensus has it mainly negative to neutral much of first half of Jan.

12Z ensembles are still cold dominated in the E US day 9+: - 12Z GEFS is colder than 6Z, which was overall slightly warmer (by 4 HDD) than the then coldest run to date 0Z and looks to be back at least about as cold as 0Z. Did it gain at least the full 4 HDD back? I’m guessing yes, which would mean at least tied for coldest run yet. - 12Z EPS looks colder than 0Z, which was overall a bit warmer than yesterday’s 12Z, which had been the coldest run to date. The 0Z was 6 HDD warmer than yesterday’s 12Z. But today’s 12Z EPS may be back to at least as yesterday’s 12Z. If so, it is at least tied for coldest run yet. I’ve said this before and feel it deserves to be repeated for readers who don’t come here often and thus who may be confused. Based on some of the posts ITT, a reader not too familiar might not realize the cold potential in the E US for at least much of the 1st half of Jan. The potential is very real and is not baseless hype, which I actually hate. Model consensus has been insisting on this being likely. It will of course warm back up eventually. That’s obvious. But well before that we have the strong cold potential. It looks like the most intense cold would likely come in at least two waves meaning warming in between of course.

PNA update: 1. The PNA after applying a rough 1.8 tabular conversion factor is roughly +1.8 MTD. It will be dropping for the rest of Dec as has been well predicted by GEFS means since the Dec 14th run. But I maintain that won’t be enough to prevent 2024 from having a decent shot at the record high Dec +PNA for non-El Nino, which is currently 2020’s +1.58. My current projection is for ~+1.45 to +1.70. So, it will probably be pretty close. The 2nd highest for non-Nino is 1960’s +1.46. So, I still think there’s a very good chance that 2024 will exceed the current 2nd highest and end up either highest or 2nd highest for non-Nino Dec PNA. (Records go back to 1950.) The reason I’ve been posting a lot about the strong Dec +PNA projection is that there’s a significant tendency for a strong non-Nino Dec PNA to carryover to Jan. As posted previously, the average Jan PNA for the non-Nino winters with the strongest 5 Dec PNAs on record has averaged +0.9 with 3 of the 5 Jans strong (within top 9 for non-Nino Jan): +1.51 (2001), +1.41 (1981), and +0.97 (1986). The other two were either weak +PNA (2006’s +0.43) or neutral (2021’s +0.19). 2. Even more significantly when looking ahead to Jan, especially with a strong -AO and moderate -NAO being predicted as well as a favorable for cold MJO, is to note that today’s 0Z GEFS based PNA prog for the 1st week of Jan has risen notably (see images below) and easily has the highest of the last 6 runs going into Jan as the 0Z GEFS maps showed a significant shift toward recent EPS runs: Here’s yesterday’s to compare to: Tabular monthly PNA since 1950: https://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/norm.pna.monthly.b5001.current.ascii.table

MJO forecasts: pretty consistent with the often favorable for cold E US with still having weak left side

Merry Christmas and also Happy Hanukkah as it starts later today. 0Z ensembles: 1. Whereas EPS retains a very cold look at 500 mb at the end and is still cold overall especially at the end, the total HDDs of the run dropped some vs the 12Z. Thus, today’s Weekly for 1/6-12 may not be as cold. 2. Bigger news: Last 2 runs of GEFS have gone a long way toward the EPS. HDDs are up significantly. The end of the 0Z GEFS is even colder than the 0Z EPS or even the 12Z EPS. The end is the coldest GEFS run yet vs the extended portions, which go out further at 0Z, of prior 0Z runs. The very cold end has MB 850s covering almost all of the E 1/2 of the US:

Way up will go the HDDs it appears as of now! 12Z EPS US pop weighted HDDs in purple on left is a bit colder than the 0Z (yellow). Green is normal. They’re progged to double between 12/29 and Jan 4th:

Today’s Euro Weeklies for Jan 6-12 has the 3rd shade of cold covering most of the E US vs just a tiny area in the 3rd shade mainly in NC the last 4 days. The third shade is 3-6C BN or 5.4-10.8F BN averaged over a full week! That’s easily the coldest EW map that I have saved in my files (all from the last 3 winters) in the SE for a week that doesn’t even start for 13 days. Note how far out this 3rd shade goes offshore as well as deep into FL: @pcbjr Precip anomaly map is similar to the CFS map I posted earlier: this has NN in the SE, which is as much as I’d ask for with it this cold. The green in the N Gulf suggests the possibility of a Miller A Gulf low: The following week (1/13-19) is also cold though it only shows the 2nd shade of blue so far (still 20+ days out). ————- Edit: The only other EE map I have that is comparable (slightly warmer SE) with most of the SE US in 5.4-10.8F BN is closer in at 9 days out (11/23/24) preceding Dec 2-8. How did it verify? Wilmington, NC (map: ~-6F): actual was -10.9F (so, it wasn’t nearly cold enough) Savannah (map ~-5.5F): actual was -9.7 (so, it wasn’t nearly cold enough) If this verification were to happen to be an indication of what’s to come Jan 6-12, the SE (at the very least) would verify colder then what today’s map shows. Also, if the strong cold signal maintains itself, look for a portion of this going into the 4th shade of blue on a run within a few days. The 4th shade starts at -10.8F.

It’s as big as any I can recall. The size of the area in the 3rd shade of blue off the E coast is the most impressive I can recall. It isn’t easy to get that offshore as we know. Looking back in my saved maps, today’s EW map for 1/6-12, with it covering most of the E US in 3-6C/5.4-10.8F BN is THE coldest of any I have in the E US for the week still being 13 days out! The only other one I have that is comparable (slightly colder NE/slightly warmer SE) with most of the E US in 5.4-10.8F BN is closer in at 9 days out (11/23/24) preceding Dec 2-8: How well did this 9 days out map verify for 12/2-8/24? NYC (map: ~-5.5F): actual was -5.3F (so, very close) Wilmington, NC (map: ~-6F): actual was -10.9F (so, it wasn’t nearly cold enough) Savannah (map ~-5.5F): actual was -9.7 (so, it wasn’t nearly cold enough) If this verification were to happen to be an indication of what’s to come Jan 6-12, the SE (at the very least) would verify colder then what today’s map shows. Also, if the strong cold signal maintains itself, look for a portion of this going into the 4th shade of blue on a run within a few days. The 4th shade starts at -10.8F.

New Euro Weeklies: For Jan 6-12: H5 has the strongest negative anomalies yet with a whopping 13-14 BN at NYC with 536 dm for a full week! The PV is centered near 70N, 80W over far N Hudson Bay. The W ridge is a bit further east vs yesterday along W coast meaning stronger +PNA, thus bringing the center of the cold back to the E US like was the case before yesterday. The Aleutian low is the strongest yet. H5: 1/6-12 2m: 1/6-12 is as Mitch just said colder in the E US though it isn’t as cold W/NW of Chicago, where the center of the cold was yesterday. Today’s has the 3rd shade of cold covering most of the E US vs just a tiny area in the 3rd shade mainly in NC the last 4 days. The third shade is 3-6C BN or 5.4-10.8F BN averaged over a full week! The subsequent week, 1/12-18, is still cold/slightly colder SE vs yesterday though not as cold Midwest with like the prior week having the W ridge a bit further east along W coast. This run keeps a pretty stout +PNA much of Jan.

How about this earlier in the 12Z EPS (at 270)?This has E NC at 20 dm BN and NYC at only 532 dm, which is 17 dm BN! I’d say that’s ~equally impressive to the further out but not quite as cold 360 hour map posted above:

How about this earlier in the 12Z EPS (at 270)? This has E NC H5 at 20 dm BN!