GaWx

Well, we're now only one day away. Here's the 12Z run update for today for the highest SLP in mb in the lower 48 on 12/22 vs runs from 24 hours ago (1064 is all-time lower 48 record back to late 1800s): GFS 1067 (0) JMA 1065 (+1) ICON 1063 (-1) Euro 1059 (-1) CMC 1059 (0) UKMET 1052 (+1) AVG ~1061 (no change) The UKMET is either going to shine or fail with their continued much lower SLP vs other models. If I throw out the highest and lowest, the average is 1061.5 mb. Friday is going to be one of the most dramatic days in a long time for the entire SE! *Edit: The 12Z NAM runs have 1067-8 mb depending on the resolution!

The 12Z UKMET has light accumulating snow over far N AL/GA on 12/26 followed by light accum snow over part of C GA, SC, and SE NC that night.

The 12Z Euro (and last few runs) is trending to somewhat more robust at H5 with the lead post frontal disturbance for early 12/26, but it still has nothing to show for it (too dry) at the surface. This run then has a more robust follow up disturbance at H5 (it is quite impressive) along with it being colder over the SE vs prior runs meaning a later ending window for possible wintry precip. It is faster moving than on the 0Z run and has light snow over N AL from this late on 12/26 to early 12/27. It also has cold rain (39F) as far north as Daytona Beach early 12/27 as a weak surface low forms just NE of the Bahamas. These disturbances are still 5-6 days away from the SE and are still well out in the Pacific with a huge Arctic high to precede them. Thus, the uncertainty level for what the SE will or wont experience on 12/26-27 is still high and higher than normal for 5-6 days out.

Thanks. My statement about this being the first run like this was incorrect and I'll edit it out. I had a brain fart as you're correctly pointing out that this timeframe has had a signal on the models for a week now. On the GFS, the 0Z 12/14, 0Z 12/15, and other 12/15 runs had significant wintry precip going deep into the SE late 12/25 through 12/26 and I even posted clown maps for three of these runs lol.

Yesterday's and this morning's cold rain (much needed) was by far the heaviest here in months with 1.50"!

Fwiw regarding the first post frontal upper level disturbance, the 12Z GFS has on 12/26 snow virga over far S MS at 6Z, S and C GA at 12Z, and at the NC/SC border near the coast at 18Z. This is not the first run doing something with this as several GFS runs on 12/14 and 12/15 had significant wintry precip deep into the SE late 12/25 into 12/26. Is this a sign that this disturbance could do more over land in future runs ~12/26 being that this is still 5 days out in a complex/highly anomalous pattern? FYI, this run has a 1067+ mb high over MT on 12/22. The alltime record is 1064. It is very likely overdone somewhat, but even so we're still looking at a good chance for the strongest lower 48 Arctic high since 12/1983. Any opinions? *Edited for corrections regarding past GFS runs for 12/26

Based on the pre-Euro 0Z model consensus, I'd say we're no closer to eliminating the possibility of significant winter precip in the deep SE ~12/26-7. As a matter of fact, this GFS run was the closest call in several days. We're still 5-6 days out and lots can change on the modeling in this highly complex setup that likely includes the strongest SLP in decades. Keep in mind that the energy associated with the 12/26-7 threat is still thousands of miles offshore the US west coast and won't be coming ashore for nearly 3 days.

Besides the strong cold, itself, it looks like to me as of now that there are two packets of energy that the models are harping on after the cold arrives: - one that hits the NW US coast late on 12/23 followed by a dive down to the Gulf compliments of the +PNA and with it affecting the SE to a quite unknown degree ~12/26-7, when it is still cold enough for potential wintry mischief - one that hits the NW US coast only one day later that also dives and then affects the SE to an unknown degree ~12/27-8, when the air modifies enough such that wintry mischief wouldn't be as easy to occur in the more southern areas And then we have a highly anomalously strong Arctic high (possibly the strongest since 12/1983) with Siberian origins in the mix. So, it isn't a simple pattern for the models to resolve over the next 8 days or so. Keep in mind that the two aforementioned packets of energy don't leave the relative data deprived ocean for still 3-4 more days.

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.