GaWx

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!

The 12Z EPS 360 hour has about as negative H5 anomalies as I can recall on any run at 360 centered in the E US. NYC is at 534 dm, which is a whopping 14-15 dm BN! Keep in mind that that is a 50 member ensemble mean out 15 days, a very difficult modeled anomaly to have.

The 12Z EPS 360 hour has about as negative H5 anomalies as I can recall on any run at 360 centered in the E US. NYC is at 534 dm, which is a whopping 14-15 dm BN! Keep in mind that that is a 50 member ensemble mean out 15 days, a very difficult modeled anomaly to have:

OISST 3.4 ERSST/OISST anomalies dropped 0.40 C/0.47 C in 2008 from Nov to Dec. This could easily end up near a 0.5C drop for OISST which would be a new record Nov to Dec drop for La Niña back to 1950.

Compared to the 18 cold ENSO Jans since 1991: the mean of the last 12 runs of the 4 member CFS ensemble has the SE at the 3rd coldest Jan 7-13 for cold ENSO behind only 2011 and 1996 with an avg of ~4.5-5F BN: Just one week ago, this is how much warmer the 12 run CFS ens mean was: ~2F AN Getting a week to average 5F BN is not the least bit easy! Precip is ~normal, which is good because that is wetter than the majority of cold periods since cold is more often than not associated with BN precip in the SE. Also, Jan 7-13 normal precip is pretty significant, especially well inland. So, it appears that there would be a decent shot at wintry precip during this period if the last 12 CFS runs have the right idea (possible Gulf moisture):

It looks like 2” at Central Park in 2009 when it was measured that was left from a big snow 12/19-20 but it was melting rapidly due to rain falling and thus was gone by 12/26: https://www.weather.gov/wrh/Climate?wfo=okx

Every one of these 5 indicators is at the coldest of the season to date clearly indicative of a rapidly strengthening La Niña to near weak/moderate Niña border on the dailies and suggesting equivalent RONI dailies probably at least high end moderate to quite possibly bordering on strong. This means a Nov to Dec cooling likely one of the strongest back to 1950 though not near the 0.8 record shattering cooling suggested by many earlier CFS runs: OISST: -0.98 C CRW: -0.95 C CDAS: -1.43 C Buoys: coldest below -1.5 C near equator along entire Nino 3.4: OHC: 0.6 C plunge just since late Nov to -1.1 C

PUBLIC INFORMATION STATEMENT NATIONAL WEATHER SERVICE NEW YORK NY 917 AM EST TUE DEC 24 2024 ..SNOWFALL REPORTS LOCATION AMOUNT TIME/DATE PROVIDER ..NEW JERSEY ..BERGEN COUNTY OAKLAND 1.0 IN 0800 AM 12/24 COCORAHS MONTVALE 1.8 ESE 0.8 IN 0800 AM 12/24 COCORAHS RIVER EDGE 0.5 IN 0840 AM 12/24 PUBLIC ..ESSEX COUNTY MONTCLAIR 0.5 IN 0800 AM 12/24 COCORAHS ..HUDSON COUNTY HARRISON 1.0 IN 0800 AM 12/24 COOP ..PASSAIC COUNTY WEST MILFORD 1.1 IN 0720 AM 12/24 COCORAHS ..UNION COUNTY NEW PROVIDENCE 0.6 IN 0730 AM 12/24 COCORAHS ..NEW YORK ..ORANGE COUNTY 0.8 N PORT JERVIS 2.5 IN 0700 AM 12/24 COOP PORT JERVIS 1.8 IN 0800 AM 12/24 COCORAHS 1 WNW MONROE 1.6 IN 0805 AM 12/24 PUBLIC ..PUTNAM COUNTY NELSONVILLE 0.3 S 1.4 IN 0715 AM 12/24 COCORAHS ..ROCKLAND COUNTY STONY POINT 0.5 IN 0700 AM 12/24 COCORAHS ..WESTCHESTER COUNTY CROTON-ON-HUDSON 1.3 IN 0850 AM 12/24 PUBLIC ARMONK 0.8 IN 0800 AM 12/24 COCORAHS SOUTH SALEM 0.5 IN 0755 AM 12/24 COCORAHS

So, are you saying Newark needs another 1.5” from this morning’s snow? I see that it had snow and only 1/2 mile visibility at 8AM. That sounds pretty significant if it had continued for awhile.

Chris, it appears NYC will get close to the 3” mark for snow in Dec that you follow during La Niña.

The bc GEFS and EPS continue to predict an MJO that would be weak left side of diagram for early Jan (see below). As mentioned, 7 of 8 similar cases during Jan for cold ENSO during last 50 years were concurrently cold dominated in the E US. Weak MJO (near or inside circle) has tended to be concurrently colder than strong for all phases in Jan after all cases were averaged. So, my hope would be for it to remain weak when later coming around on the right side: GEFS: EPS:

What a nasty late afternoon here with breezy drizzly and only 42.6 F now. CAD at its best/worst! This is easily the coldest afternoon of the season yet! I may not get a walk in. 10:45PM: Down to 41.1 with light rain. The cold has a real bite to it. 11:30PM 40.8 with light rain