GaWx

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.

Don, With NYC at +2 for 3/1-11, it will be an even bigger challenge for JB to get his -5 for 3/1-4/15. The latest forecasts seem to suggest that NYC may cool off enough to allow 3/1-20 to almost get back down to right at the 1991-2020 normal. But even if so, that would still require -9 for 3/21-4/15. The 3/21-4/15 cold in both 1956 and 1940 would get him close (to a -4). The last time it almost got to -9 for 3/21-4/15 was right at the turn of the century, the 20th century! That 1900 cold would be just cold enough for him to get his -5 with rounding. The last one to get him -5 without rounding was 1888. So, his chances continue to drop.

Fantasyland 12Z GFS Miller A GOM snowstorm very late 3/21 to early 3/23. Almost entire N half of GA to NW SC to W 2/3 of NC to most of VA gets several inches. Shades of 3/24/1983. Mainly for entertainment but there is still that second batch of cold coming per model consensus and it looks to be coming in with more moisture to play with instead of plunging down like the first one in a few days. This is the extreme of extremes of what can happen. 12Z ICON also has a GOM Miller A but two days earlier. Some snow from that west of the SE US on 3/19.

Per RDU: AS OF 400 AM SUNDAY... ...WINTRY MIX EXPECTED THIS MORNING AND INTO THE EARLY AFTERNOON ACROSS THE NORTHERN PIEDMONT COUNTIES... ...HAVE INCREASED SNOW/SLEET AMOUNTS SLIGHTLY ACROSS THE FAR NORTHERN PIEDMONT COUNTIES... ..IMPACTS STILL EXPECTED TO BE LIMITED CONFIDENCE CONTINUES TO INCREASE THAT A PERIOD OF MIXED WINTRY PRECIP WILL BEGIN LATER THIS MORNING AND COULD LINGER THROUGH MIDDAY/EARLY AFTERNOON ACROSS THE NORTHERN PIEDMONT/I-85 CORRIDOR, BEFORE EVERYTHING CHANGES OVER TO LIQUID RAIN. OVER THE PAST 24-36 HOURS, MODELS ARE LESS SUPPRESSED WRT TO STRONGER MOISTURE TRANSPORT ACROSS THE REGION. THUS, LIQUID EQUIVALENT HAVE INCREASED ACROSS NORTHERN PORTIONS OF THE FORECAST AREA, WITH FAIRLY UNIFORM LIQUID EQUIVALENT OF 0.50-0.66" EXPECTED ACROSS CENTRAL NC. HOWEVER, THE STRONGER SOUTHERLY TRANSPORT FARTHER NORTH CENTRAL NC ALSO MEANS A MODEL SIGNALING OF SLIGHTLY WARMER TEMPS ALOFT, WHICH INTRODUCES INCREASING CHANCES FOR MORE MIXED PRECIP, WHICH INCLUDES SLEET MIXING IN WITH THE RAIN AND SNOW AT TIMES. A FORECAST OF MIXED P-TYPE INHERENTLY INTRODUCES A GOOD DEGREE OF UNCERTAINTY WRT TO ACTUAL SNOW/SLEET AMOUNTS. WITH THAT SAID, THE LAST COUPLE OF RUNS OF THE HI-RES ENSEMBLE PROBABILISTIC FORECASTS CONTINUE TO SHOW LIKELY TO CATEGORICAL CHANCES OF AT LEAST A HALF INCH OF SNOW/SLEET ACROSS THE FAR NORTHERN, I-85 CORRIDOR COUNTIES. WHILE IT'S POSSIBLE TO SEE SOME LOCALIZED HEAVIER AMOUNTS NEAR THE VIRGINIA BORDER(PERSON COUNTY), THE RECENT RECORD WARMTH HAS RESULTED IN VERY WARM GROUND TEMPS. THUS, ACCUMULATIONS SHOULD LARGELY BE CONFINED TO ELEVATED SURFACES SUCH AS ROOF TOPS AND DECKS, WITH LITTLE TO NO IMPACTS ON ROADS AND BRIDGES. * Edit at 5:40 AM: sleet reported in W portion of Triad

How much does sun angle matter anywhere and at any time of year if there is a thick overcast? Anyone know?

From RDU: A COMBINATION OF TOP-DOWN AND FORECAST PARTIAL THICKNESS/TRENDS NOMOGRAM FAVOR THE PRESENCE OF A DEEP/NEAR FREEZING ISOTHERMAL LAYER ALOFT AND MELTING OF SNOW IN A SHALLOW, ABOVE FREEZING SURFACE LAYER THAT WILL LIKELY SUPPORT A LARGER AND MORE PROLONGED AREA OF RAIN/SNOW MIX OR EVEN ALL SNOW ACROSS THE NRN NC PIEDMONT SUNDAY MORNING. THAT APPEARS TO BE THE CASE AFTER AN INITIAL PERIOD OF LIGHT RAIN INCOMPLETELY SATURATING/COOLING THE SUB-CLOUD LAYER AT ONSET, THEN BOTH WARMING AND DRYING ALOFT, AND INSOLATION FROM A MID- MARCH SUN ANGLE, DURING THE AFTERNOON, WHICH WOULD FAVOR A CHANGEOVER TO RAIN/DRIZZLE THAT WILL CONTINUE THROUGH SUNDAY NIGHT. ***HOWEVER, MOST/ALL SNOW SHOULD MELT AS IT FALLS*** OWING TO 1) VERY WARM SOIL TEMPERATURES THAT HAVE RANGED FROM MID 40S TO LWR 50S F THE PAST COUPLE OF MORNINGS TO 50S TO NEAR 60 F THIS AFTERNOON, 2) ABOVE FREEZING AIR TEMPERATURES EXCEPT FOR PERHAPS A 2-3 HR PERIOD WHEN HEAVIER PRECIP RATES WOULD FAVOR "MELTING OUT"/ DIABATICALLY- COOLING TO 32-33F AN OTHERWISE ~750-1000 FT AGL ABOVE FREEZING SURFACE LAYER, AND 3) A MID-MARCH/LATE WINTER SUN ANGLE THROUGH THE MORNING-MIDDAY HOURS. ANY ACCUMULATION OF PERHAPS A TENTH TO TWO WOULD BE LIMITED TO ANY PERIOD OF ALL SNOW AND CONFINED TO ELEVATED SURFACES NEAR THE VA BORDER.

Nice beautiful, cool autumn .....ooops, I mean late winter day here. Perfect for a daytime walk with sunshine, 60s, dews in the low 40s, and a pretty sunset as a bonus!

I'm excited for you guys to see a nice fall of snow (mixed with rain). As long as expectations of sticking are kept in check (like expecting none), this looks like fun for y'all.

The 12Z GFS has RDU down to 34 and 100% RH early tomorrow afternoon with rain/snow mix falling. I'm not looking for sticking (though some sticking on nonpaved surfaces in some areas possible), but seeing some flakes falling is the main potential.

The 12Z GFS has RDU down to 34 and 100% RH early tomorrow afternoon with rain/snow mix falling. I'm not looking for sticking (though some sticking on nonpaved surfaces in some areas possible), but seeing some flakes falling is the main potential. Check out the new thread for this.

Not having seen this new thread, I just had posted this in the main one: "More immediately, there's a good chance for snow falling for part of tomorrow for especially northern NC! It would be a challenge for it to stick but not impossible in some areas for some stickage. But it just falling would be quite notable, especially for mid March and this winter's lack of it." Good luck to you guys!

The 6Z GEFS/0Z GEPS has a moderate/modest Miller A ish Gulf storm signal for late 3/19 through 3/20, but that's nearly in fantasyland. Should there be one, it could get interesting for some areas (especially NC) for wintry precip ~3/20 considering how cold the preceding airmass might be. There have been some wintry precip events during 3/19-21 looking back in history. More immediately, there's a good chance for snow falling for part of tomorrow for especially northern NC! It would be a challenge for it to stick but not impossible in some areas for some stickage. But it just falling would be quite notable, especially for mid March and this winter's lack of it.

The 18Z GFS along with recent runs has near record cold over the N Plains 3/17-18. It may be overdone due to snowcover assumptions, but regardless this shows the potential for a very potent cold airmass to come out of Canada then. I'm mentioning this only because most models then have this airmass plunge into the SE shortly after (3/18-20). Some runs, including this one for 3/19-20, have been showing the coldest of this airmass to be colder than the prior one for the SE.

Thanks for that info. I didn't mean in quite a few Marches. I meant it has been quite awhile since we had that (several freezes close together) this winter. The last time Atlanta and Athens had two consecutive freezes was way back in late January, for example.