GaWx

Check out the 0Z ICON, especially in NC/VA 3/20-1. This is from wave #1. This is way different from the 12Z.

Though it isn't looking good right now, I'd like to try to cheer up the thread with a low probability weenie map. I posted below the 6 hour qpf map for late Sun night from the weenie 12Z JMA. Because this is from the first wave, the precip occurs much earlier than the GFS' second wave based storm, which doesn't even first reach SC til 30 hours later. Almost all of this qpf north of a line from Atlanta to Athens to 50 miles S of Charlotte to S of Fayetteville and ENE into E NC is snow along with some of the qpf south of that line. The 1009 mb surface low had just crossed C FL while a cold 1033 mb high centered over NY state is still feeding in fresh cold air into the SE US on NE winds. This is the kind of map and early timing (working with the cold air rather than following it out) that is probably needed for a major winter storm in a good portion of the SE:

Other than some of the mountains, the 18Z GFS is too warm for snow in the SE. Like for recent GFS runs it brings in the precip during 3/21-2 and that is from the second shortwave, by which time the cold air has modified too much. Contrast this to the 12Z JMA, which gives much of the northern SE a major winter storm from the first shortwave 3/19-20 when the cold air is fresh. Its snow is already exiting NC before the GFS' rain even starts from the second wave!

I agree. Suppressed would imo be the best chance (not necessarily for the mountains though as they often do best in other scenarios like upslope): see the 12Z JMA for example. Its low forms way down south in the GOM and then crosses central FL but still has a multiple inch snowstorm as far north as the GA/TN border to SE VA. The non-BOMM models all have the MJO either in phase 1 or 2 during the critical 3/19-21 period. Those two phases are the most favorable for suppressed Miller A lows and are easily the wettest phases in the SE (outside of the mountains) in the period centered on March: Also, phase 2 is the coldest in the SE while phase 1 is third coldest: In summary for the bulk of the SE, the MJO can't be any more favorable than is progged for 3/19-21.

**Weenie alert** Fwiw because I know it is an inferior model, often has weenie runs, and almost always fails when it is on its own: The 12Z JMA is easily the weeniest run today. Based on 850s being sub 0C and significant qpf falling into those cold 850s, there appears to be significant to major snow over N GA (ATL to Augusta north), N SC (Aiken to Columbia to Florence north), most of NC other than coast and far west (heaviest over inland E NC including Fayetteville and RDU), and far SE VA. It starts early (which is key), 3/19, over N GA, and ends late on 3/20 over the E Carolinas. This is from that initial wave being much stronger vs other models. A very weak surface low develops well south in the GOM early on 3/19. It then moves ENE over C FL early on 3/20 to 200 miles SE of Charleston and strengthens to 1010 mb while underneath a cold 1032 mb high then centered over W NY state. Edit: this is not the same wave the GFS is developing. The GFS develops the followup and is now on its own doing so. In summary regarding 12Z runs: JMA (wave 1) and GFS (wave 2) are on their own with wintry precip in the SE. The GFS wintry is very limited (non sticking snow in C GA). The GFS is now on its own of the 12Z operationals developing the 2nd wave though some ensemble members still do. Another edit: Although the JMA is inferior, it does illustrate well that the timing of the first wave is better for a potential winter storm because the cold high to the north will have had little time to modify.

12Z Euro is more progressive with that stronger low and thus it ends up getting rain only up to coastal GA/SC/NC before pulling out and with no wintry precip. There's nothing behind this unlike the runs of yesterday and the day before, which had a stronger followup shortwave/GOM low.

As of 120, the 12Z Euro has a stronger low just off S FL and rain further north than earlier runs. Edit: north extent of rain actually about same

It is out to 96. That looks about right keeping in mind we're in DST.

The 12Z UKMET is a bit more progressive with the weak low just off FL late in the run. Despite that, a cold rain (low 40s) still moves as far north as SAV at 144. Interestingly, 850s cool from +3 C at 138 just before the rain to -1 to -2 C just after it starts at 144. That's due to evaporative cooling because 850 dewpoints are way down to -10 C just before the rain starts. With the surface then progged to be well above 32 at 43 and likely bottoming near 40, I wonder whether it would be too warm for any mixed precip to briefly make it to the ground at the end of that run. The output doesn't show precip type.

KSAV had a low this morning of 34, the coldest since January 28th! Due to much better radiational cooling conditions tonight and despite warmer 850s and probably a slightly warmer high today, they probably will end up slightly colder tomorrow morning with a freeze quite possible. The coldest in Feb was 36. Dewpoint is now only 17!

Anomalous is more interesting to me from a forecasting and observational perspective. Different strokes for different folks. The 0Z UKMET through 144 adds a new scenario of the precursor low moving slowly NNE off FL almost directly toward the cold high instead of OTS. This results in a cold rain moving north earlier into SE GA and then S SC on 3/20. None is wintry temperatures in the 40s) but I wonder what the later frames will show that go out another 24 hours assuming it gets to NC. The cold is retreating but I'm not sure it will do so quickly enough to avoid some form of wintry in NC on the later frames. Edit: Interestingly, the 0Z Euro has a similar change to the 0Z UKMET with the precursor low moving NNE instead of further offshore. This leads to light snow in parts of upstate SC and NC. This change in these two models is making me wonder if we're eventually going to get an up the coast nor'easter out of this as the dominant low as opposed to a more classic GOM low. Could the very warm waters of the SW Atlantic lead to this?

The ship hasn't quite left the dock. It is giving the ducks one last chance to board early next week. Will they board early next week or will they be left behind til next winter? I just did a check of old maps for the two week periods centered on March 20th going back to 2000. I was looking for a similarly tracking GOM Miller A type low with a Canadian high to its north when over the E coast with a SLP comparable to what's progged for early next week (~1035 mb). The closest I could find was 3/13/2017. The high was about that strong but it wasn't quite as cold preceding the low vs what's progged. My point is that the projected setup is highly anomalous for this period. I'll try to check before 2000 later. The 18Z EPS had more activity offshore FL with the predecessor low fwiw.

- It would be better if it were about a day earlier so that the cold air has less time to modify. - 12Z UKMET and Euro are good examples. - The UK has a nice Gulf low, but by the time it starts to bring its precip into the SE, 850s are already warming to above 0C ahead of it at the end of the run (Tue at 8AM). It also had a weak precursor wave just east of FL early on Mon (3/20) due S of the mid-Atlantic Arctic high that remained too suppressed and weak to get precip far enough NW into the sub 0C 850 mb air. - If future runs were to show a stronger and further NW offshore SE precursor low on 3/20, that could easily produce wintry on its own. The 12Z Euro hinted at that with small areas of mixed precip over S AL and C GA/SC (even in the afternoon in SC) on 3/20 from its precursor.

It probably needs to come in earlier, similar to the timing of the Euro's weaker low offshore FL the day before, to take full advantage of the cold air before it modifies too much. That earlier weaker low actually produced light mixed precip in a few spots in GA/SC the day before (3/20). Several runs of the ensembles have shown this predecessor low offshore the SE. The ducks remain on the pond. So, at least they're very persistent. But will they end up quacking?

- I'd put the 12Z UKMET in that category. - The 12Z ICON and CMC have nothing all that threatening. - Regardless, the strongest signal so far this winter for a *potential* significant snowfall remains and is making this easily the most exciting period regarding winter storm potential for the SE forum to this point. There's a good chance for a thread for this in the near future. Of course, that doesn't necessarily mean this storm will actually occur. - This doesn't mean that some of these GFS clown maps aren't absolutely ridiculous lol. But a rather widespread area of multiple inches of wet snow favoring inland and more northern areas of the SE is a reasonable possibility considering the many runs having it, how cold the preceding airmass is (-15C at 850 in NE TN two days prior, very rare for mid March that far south), having the Canadian high skirting by to our north rather than plunging, having a 50/50 type low to slow down cold modification, progged moist WSW H5 flow/split flow with good chance for a GOM low, having the most supportive MJO phase for March (2), and this is now earlier than fantasyland. - As shown earlier, longtime climo isn't exactly nonsupportive with an average of one every 10 years (especially in NC) though RDU is way overdue for 1"+ near this period as it has been 40 years! - The -15 C progged at 850 for 3/19 in NE TN is something like 18 C BN for the date meaning about as cold as it ever gets at 850 there then. This would be well BN even in January!

How realistic is the possibility of a significant snow hit for RDU early next week? Here's some history of 1"+ within a week of this period: (3/13-28) 3/18/1893: 1.5" 3/20-21/1908: 2.3" 3/22/1914: 3" 3/13/1926: 4.2" 3/15/1934: 2" 3/24/1940: 7" 3/13/1941: 1" 3/27-8/1947: 2.8" 3/15/1952: 1.2" 3/25-6/1971 5.4" 3/25/1972: 2.6" 3/25/1974: 2.5" 3/24/1983: 7.3" - So, there were more than I expected, 13. This means they've occurred about once every 10 years on average. And this isn't even including the smaller snows! - They're way overdue as it has been 40 years since the last one! Before this, there had been no more than 19 years between them. - Oddly enough, the heaviest and most frequent were late rather than early with 3/24-6 dominating! - This all tells me that getting good snow early next week at and near RDU is a reasonable hope.

Followup for @donsutherland1 and others: 1. RDU did actually get snow and sleet yesterday, but there was only a trace vs that CFS run's wintry precip that lead to 1" of snowcover. 2. The actual high yesterday was only 41. So, although the CFS' ~36 did end up too cold, the other models with their mid 40s to low 50s were all too warm with some ~10 too warm. 3. The actual 12Z (8AM EDT) temperature today was 40. So, the CFS' 32 verified 8 too cold. But the Euro's 49 was 9 too warm. The other 4 along with the NWS were also too warm but only by 2-3. 4. In summary the CFS verified too snowy and cold as expected, but the others were too warm.

It is all about the potential since this regards 7-8 days out. This 12Z EPS linked map to individual member SLPs tells me there's potential with many members having an offshore SE coast low; a strong (1035ish), pretty large, and very cold high for March 20th in a near perfect position moving by in the climo favored path well to the north instead of plunging down and keeping it dry; CAD potential; a 50-50ish low to keep it from modifying too quickly; and it holding cold enough at 850 past this period for much of inland SE. It would be a challenge due to it already being March 20-21 then, but we already knew that and significant SE wintry precip has happened then and even later. The MJO is supportive and there is even a weak +PNA and -NAO along with a just passed secondary -AO peak. The ducks are there right now. Will they stay? Edit: linked 12Z EPS map: https://www.pivotalweather.com/model.php?m=epsens&p=sfcmslp-meanmem&rh=2023031312&fh=168&r=conus&dpdt=&mc=

I just checked Houston records and it appears that the latest in the season wintry precip on record was on 3/27/1930, the only one on 3/18 or later. I checked nearby cities and found that Austin had 0.1" on 3/27/1930 with a high of 42 and low of 34. So, the T at Houston appears legit. The main point here is how unusual a setup is indicated for that period.

12Z Euro has mixed precip along the TX coast at 180 hours. Temps are in the 40s, but still that's quite remarkable. Edit: 12Z Euro mixed precip on 3/21 Augusta to Charlotte corridor. Link to mixed precip TX coast on 12Z Euro at 180 for @Ed, snow and hurricane fan https://www.pivotalweather.com/model.php?m=ecmwf_full&p=prateptype_cat_ecmwf-imp&rh=2023031312&fh=180&r=us_sc&dpdt=&mc= 2M temps are in the mid 40s but 850s are only in the +1C to +2C range on the TX coast then. Edit: So, I think this is the first Euro run with any SE wintry precip from the offshore low.

Together with the 12Z ICON close call, the 12Z GFS on 3/21 and CMC on 3/21-2 having actual wintry precip in some areas of the SE tells me the winter storm signal is still very much intact and probably increasing. Details on operational runs are unimportant this far out. MJO phase 2 is the most supportive phase for cold and precip (specifically from GOM lows) this time of year fwiw and that's about where it is projected to be by most models then. Per my memory, this already appears to be the strongest threat of a winter storm in a decent portion of the SE within 8 days so far this winter. It may not materialize, but at least it is a nontrivial possibility in contrast to just about the entire cold season so far. Edit: 12Z GEFS GOM to offshore SE US storm and cold signal for 3/20 is rather impressive. This continues through 3/21 with another batch of GOM storms then, which are closer to the coast.

The 12Z ICON has a close call to an inland SE winter storm late 3/19 through 3/20. To show how uncommonly cold it is on this run, it has highs way down here only in the low 50s on 3/19 and upper 40s on 3/20, both near record low highs due to clouds/rain. NC has highs only in the 40s on 3/19 and mainly low 40s on 3/20. RDU's record low high for 3/20 is 41.

Looking good. A moderate signal for a very rare (for this time of year) winter storm remains intact for somewhere in the SE within 3/19-22. This is still mere speculation since it is still a ways out (6-9 days), but the ducks are on the pond at least and they're not flying away. There seems to be at least a small chance of something major wintrywise and a moderate chance for something nonmajor.

Looking at the progged indices for this extreme fantasy period of 3/19-22: 1. There's a weak +PNA peak, the highest PNA in 6 weeks, that then drops to neutral. 2. There's a secondary moderate -AO dip likely influenced by the lagged effects of the combined mid Feb SSW and late Feb further weakening. 3. There's a weak -NAO. 4. The MJO looks to be in moderate phase 1 to 2. Those on average for the SE during Feb-April have been two of the coldest phases (2 being the coldest) and the two wettest (suggesting the two phases most supportive for a Miller A per the precip patterns shown) as per below: Note that the 12Z CMC, EPS and GEFS all have a moderate Miller A signal within 3/19-22. Also, note that the consensus is bringing down a very cold airmass for mid March of sub -20C at 850 mb into the Midwest along with a large and strong (~1040 mb) surface high. Furthermore, the models aren't plunging it deep into the SE, which would be a dry cold. Rather, they're bringing the center of it to the Ohio Valley or nearby, which is conducive to potential Gulf centered action underneath, while showing a typically moist WSW H5 flow over the top in the SE (kind of a split flow). All of these are the "ducks on the pond" that suggest to watch this period for a *potential* rarity in mid to late March.

The 12Z Euro doesn't have a SE winter storm for 3/19-20. But, dare I say, the setup at H5, 850 mb, and at the surface is about as good a look as you're going to get without actually showing one in mid March for a *potential* very rare major snowstorm. When combined with what the 12Z ICON and GFS have, let's just say that I'm not counting out a miracle for somewhere within 3/19-22.