GaWx

Update for 12Z runs today for the highest SLP in mb in the lower 48 on 12/22 vs runs from 24 hours ago: GFS 1067 (0) ICON 1064 (-4) JMA 1064 (+1) Euro 1060 (-1) CMC 1059 (-2) UKMET 1051 (0) AVG ~1061 (-1) Record 1064 If I throw out both the highest and lowest, the average is ~1062. We're still looking at a highly anomalous Arctic plunge coming up, something that the models will not be able to handle easily. Thus expect extra high model volatility and disagreement to continue for the SE, especially for 12/25-8. Also, 12/23 is going to be an amazing day for weather lovers as the extremely strong cold front plunges down, something not seen often.

Further to the above, the 12Z EPS shows a rather strong signal (much stronger than earlier runs) for a surface low offshore the SE at 162 (1 AM 12/27). Keep in mind that this is about a week out, which is still plenty of time for significant changes on the models:

The period ~late 12/26 to early 12/27 still looks somewhat up in the air to me for the SE, especially near the coast, for wintry (mainly for ZR or IP) when seeing maps like the one below from the 12Z Euro. This shows very light rain for Jacksonville, FL, while the rain is just offshore GA/SC where temps are in the high 30s, wetbulbs are near 32, and 850s are still only ~+3 to +4 (cold enough to possibly support ZR). Though the odds remain pretty low, it wouldn't take too much of a change for this to instead be a stronger coastal storm with wintry precip:

Update for 12Z runs today for the highest SLP in mb in the lower 48 on 12/22 vs runs from 24 hours ago: ICON 1068 (+3) GFS 1067 (-1) JMA 1063 (-1) Euro 1061 (-1) CMC 1061 (+2) UKMET 1051 (-1) AVG ~1062 (no change) Record 1064 UKMET as it has been on the other days I've checked is a strong outlier on the low side. If I were to throw out the lowest and highest (UKMET and ICON), I'd get an average of 1063, which compares to 1062.5 from 24 hours ago.

The 12Z JMA at 192 hours (12Z on 12/27) on TT has a strong wedge extending quite deep into the SE from a 1037 mb NE high and a weak N GOM low forming as the jet buckles. Precip is breaking out before hour 192 (late 12/26-early 12/27) over LA, C and S MS and AL, west central and SW GA, and NW FL with 850s between -2 C and +5C. Based on past Gulf lows with a strong wedge north of them and 850s this cold, this area of precip is likely mostly wintry of various forms, with snow falling in the N portion of the precip from far N LA to part of SW GA (where 850s are below 0C) and IP/ZR due to the strong wedge likely reaching almost to, if not to, the Gulf coast, including much of NW FL and as far SE as near Gainesville.

Further to the above, 12Z Euro case in point! This period is hardly settled.

1) I find it very interesting that the heart of the very cold plunge in the SE will be during the MJO "warm" (MC) phases 4 and 5 and outside the COD! That is obviously not a common occurrence. This shows that the MJO, like most indices, is just one "tool" among many to utilize for forecasting and that by itself isn't necessarily going to be the main driver. The main drivers appear to be the continued very strong -AO along with a moderate +PNA. 2) This 12Z ICON map, which is quite different from where the 0Z was going, is another that tells me that it is still not a safe bet that there won't be significant wintry precip of whatever variety in the SE ~12/26-7. Even though the odds are rather low based on the lack of that actually showing on the latest model consensus, I'm still focusing around that time for the possibility of a "surprise" based on pattern recognition. Whenever I see WSW or SW 500 mb flow over the top of a very cold Arctic airmass that is slow to pull out, I keep a wary eye. Keep in mind that this potential is still at least nearly a week out. That is far enough out for the very imperfect models to have a hard time, especially with the very highly anomalous setup associated with the progged near record breaking pressure in Montana in three days:

We had the coldest so far this season this morning with lows of 29/28 at the airport/Hunter. Loving it! As a result, I had my coldest walk yet so far this season with upper 30s last evening.

The upcoming strong cold should keep it interesting here. Meanwhile, maps like these from the 0Z CMC are keeping me somewhat interested in ~12/26 as it wouldn't take a whole lot of adjustment for something still a week out to bring wintry precip at least to the SE coastal areas even with odds not high and getting lower:

The Euro is forecasting KATL to stay at or colder than 32 on two straight days, 12/25-6. That doesn't occur often. It has been nearly nine years. When were the last times for this or longer over the last 50 years? 1/28-9/2014 1/8-9/2010 12/21-22/2000 1/4-5/1999 2/3-5/1996 1/15-16/1994 12/22-23/1989 1/6-8/1988 12/24-6/1983 1/10-14/1982 1/13-15/1978 1/17-19/1977 1/8-10/1973 There hasn't even been a single day not getting above 32 since 1/2018.

Update for 12Z runs today for the highest SLP in mb in the lower 48 on 12/22 vs runs from 24 hours ago: GFS 1068 (-1) ICON 1065 (0) JMA 1064 (-4) Euro 1061 (-3) CMC 1058 (-5) UKMET 1052 (-2) AVG 1061 (-3) Record 1064

I'm nowhere near giving up on 12/26 yet with it being still a week out. Here is the 12Z GFS:

I find it quite interesting that the strongest of the cold will be mainly during the usually warmer MC MJO phases (4 and 5) per the GEFS and EPS. I wonder if this could end up as the coldest airmass with the MJO there since MJO daily records started in the middle 1970s.

The 0Z ICON has outdone itself with a forecasted 1069 mb on 12/22!! Highest US SLP I have found so far on any model for that day. That's 31.57"! Record high is 31.42".

Followup with todays 12Z models for highest SLP on 12/22 in MT/WY along with change vs the runs from 24 hours earlier: GFS 1068 (+3) JMA 1068 (+7) ICON 1065 (-2) Euro 1064 (-1) CMC 1063 (+3) UKMET 1053 (+3) AVG 1063.5 (+2) Record 1064 The point is that we're headed to a very highly anomalous setup next week.

The 12Z GFS was as mentioned the first run in five with a western GOM low on 12/26. But it was very weak and later sheared out. Now the 18Z GFS is still another step closer to a potential big deal very deep into the SE late 12/25 through 12/26. H5 flow is WSW instead of W along the Gulf coast and there's more Gulf and S half of FL qpf. Some qpf even reaches the NC OB with temps barely above 32. Very cold air is then still deep down into the SE. Keep watching this period as it clearly has potential to be a really big deal with just some not so big adjustments, including the common NW track adjustments. Whereas 12/25-12/26 is still somewhat out in fantasyland, it is persisting as a threat as we get closer and closer. The first GFS run with a deep SE winter storm late 12/25 through 12/26 was the 0Z 12/14 run. At that point, it was 12 days out. That period is now only 8 days out and the threat has still not gone even with no actual winter storm yet reappearing on the GFS. Getting a winter storm deep into the SE is rare. But the Arctic high progged for 12/22 in MT is knocking on the door of a new record high going back to the late 1800s. So, the general setup is very highly anomalous.

The Euro is not far from wintry in part of the SE ~12/26.

Though it may be subtle, the 12Z CMC especially and the GFS to a lesser extent had changes vs the 6Z/0Z that went in a good direction toward possibly reviving the 12/26 threat. The CMC has a storm form offshore the SE that actually gives some sleet to coastal NC while the GFS has a W GOM low (though weak) form for the first time in 5 runs.

For a wx history lover like me, the highest Montana/N Wyoming SLP next Thursday will be fun to track. That's because the 12Z ICON forecasted a max of 1067 mb on 12/22 and both the 12Z GFS and Euro forecasted 1065 mb on 12/22 in that area, which would be a new record high for the lower 48! The highest on record back to the late 1800s is 1064, set in Miles City, MT, on 12/24/1983. The 2nd highest is 1063.3 mb, which was at Helena, MT, on 1/10/1962. But the other three main models are lower. On 12/22 the 12Z JMA is at 1061, CMC is 1060, and the UKMET is only near 1050. So, we'll see whether or not these ICON/Euro/GFS runs end up too high. The odds are that they're too high but that remains to be seen. On 12/24/1983, the PNA was -1.1, the AO was +2.8, and the NAO was 0.0. On 1/10/1962, the PNA was +0.5, the AO was -+1.1, and the NAO was +0.9. Per today's GEFS forecasts for 12/22: 1. PNA neutral and rising 2. AO still very strongly negative 3. NAO neutral and rising What might this very strong high portend for the SE US? To get an idea of the potential, let's look at what the 1983 and 1962 Arctic highs lead to at ATL and RDU: At Atlanta: - The 12/24/1983 high lead to 3 days in a row that didn't exceed 32 (12/24-26) with a coldest of 0 on 12/25. They had some ZR on 12/27 as they warmed. They had a followup cold blast that got them down to 10 on 12/30. - The 1/10/1962 high also lead to three days in a row that didn't get above 32 (1/10-12). Atl got down to 8 on 1/11. It also had 3.5" of snow preceding it on 1/9. At RDU: - The 12/24/1983 high lead to two days in a row that didn't rise above 32 (12/25-6) and a coldest of 4 on 12/25. They then had some wintry precip on 12/28 as they warmed followed by another cold blast that got them down to 11 on 12/31. - The 1/10/1962 high lead to two days in a row that didn't get above 32, 1/11-12. Their coldest was 5 on 1/11. This was preceded by 5" of snow on 1/10. US pressure records from here: https://www.wunderground.com/blog/weatherhistorian/world-and-us-anticyclonic-high-barometric-pressure-records.html

Whereas the 0Z GEFS backed down on a coastal 12/26 threat, the 0Z Euro did the opposite. It had at 240 in the SE Gulf a weak low that appeared ready to make a turn NE across FL and strengthen. This would be due to the 500 mb flow becoming a more moist SW in response to strong upper level energy diving SE from Canada. Cold enough air at the time was still along the coast. Had this run gone just a little bit further, I think it would have shown a coastal SE winter storm. More importantly, the 0Z EPS supports the Euro with a good number of members as well as the mean looking threatening on 12/26. In addition, 8 of 20 (40%) of 0Z GEPS members have wintry precip, mainly ZR, to the coast on 12/25. Edit: 6Z GFS is MUCH warmer on 12/26 with no winter storm anywhere closeby, following the lead of the 0Z GEFS.

Whereas the 18Z GFS backed off for 12/26, the 0Z brought it right back as a sleet/snow mix to the coast and inland 25-50 miles. See map below, which counts it all as snow and thus inflates the amounts. Further inland is all snow. This makes the 0Z GFS a highly unusual 5th of the last 9 and 3rd of the last 4 with significant wintry precip all the way to the SE coast on 12/26 fwiw (still not much value other than entertainment that far out). OTOH and more importantly since ensemble means have a good bit less inaccuracy than operational runs, the 0Z GEFS mean has the 500 mb trough a good bit west of earlier GEFS runs and is thus warmer/too warm for coastal wintry precip. on 12/26. Since having a winter storm on the coast of this magnitude is rare (only once every 20 years in our area), I normally view modeled winter storms in our area with a lot of doubt since most don't materialize. Let's see whether or not this GEFS run is a harbinger of GFS future runs.

Good point though since we're talking 11 days out (well out in almost unforecastable fantasyland) a lot could and probably will change as you know. But fwiw the 12Z EPS mean (and some other recent ensembles to an extent) has a textbook setup for a rare SE winter storm of some form near 12/26 that includes the coast because it is so cold. The mean 500 mb trough is centered to the west allowing for a moist WSW flow on top of the very cold air forecasted to be already in place. The mean qpf is most concentrated from the FL panhandle through the eastern sections of GA, SC, and GA. So, still just a far out fantasy, but rather interesting.

For the record/entertainment since it is still way out in fantasyland (12/26), a large portion of that 2nd storm is sleet/ice during the majority of it within 75-100 miles of the GA-NC coast as 850 mb temperatures are or go above 0C. The 6Z GFS was colder at 850 with more snow but it had a lighter event. Regardless, the 12Z GFS is the 4th with significant wintry precip to the SE coast on 12/26 fwiw (still not much value other than entertainment that far out).

And this 0Z GFS storm is in reality actually almost all snow since 850s are all below 0C. The southern part of this goes all of the way down to the FL/GA border! This is still way out in fantasyland and is thus mainly for entertainment as of now. However, this is about the third GFS run over the last few days showing SE coastal wintry precip. The 0Z 12/14 GFS also had a winter storm for the same timeframe that included the SE coast though it was mainly IP/ZR there (see 2nd image). This one, like that one, actually starts on 12/25 and thus would mean a white Christmas for many! From 0Z 12/14 GFS run: This was the first one showing significant wintry precip for the coast (mainly IP/ZR with this from the 18Z 12/12 run for 12/27):

Followup as I just compiled the effects on RDU and ATL from the strongest -AOs averaged out 12/16-31 since 1950. 2022's 12/16-31 is per today's GEFS flirting with ending up with an average of near -3. Here are the strongest: 2009: -4.5 1950: -3.8 2010: -3.7 1976: -3.5 2000: -3.4 1995: -2.8 So, 2022 is as of now aiming for 6th or 7th strongest 12/16-31 -AO since 1950. That would mean 92-93 percentile. How were these six last half of Decembers at RDU and ATL in terms of temperature anomaly, lowest temperature, and wintry precip? 1) RDU: 2009: 6 BN, 23, 0.2" SN/IP 1950: 9 BN, 13, 0.3" SN/IP, 0.41" ZR 2010: 8 BN, 19, 7.5" SN/IP, 0.47" ZR 1976: 6 BN, 9, 0.0" SN/IP 2000: 11 BN, 12, 0.1" SN/IP 1995: 8 BN, 18, 0.0" SN/IP AVG 8 BN, 16, 1.4" SN/IP, 0.15" ZR 2) ATL: 2009: 5 BN, 27, T of SN/IP 1950: 6 BN, 18, 0.0" SN/IP, 0.77" ZR 2010: 5 BN, 23, 1.4" SN/IP 1976: 7 BN, 13, 0.0" SN/IP 2000: 13 BN, 13, 3.0", SN/IP 1995: 7 BN, 21, 0.0" SN/IP AVG 7 BN, 19, 0.7" SN/IP, 0.13" ZR What does this tell me about the last half of this month in the SE? 1. Cold to very cold most days very likely. 2. Good chance for RDU coldest to be teens and ATL coldest to be teens or low 20s. 3. Assume non-cold dominated operational runs not supported by ensembles are likely wrong. 4. Significant wintry precip hard to predict as is normal for the SE. One third of the analogs at RDU and half at ATL had significant. That's a larger % than the overall climo % for just the last half of December, which is intuitive since it is so cold. Thus the average wintry precip for the six analogs is well above normal for that period even though there could still easily be nothing significant or possibly none at all.