GaWx

KATL did it. They had a low of 28 this morning, making it the coldest of the year to date and since way back on 12/26/2022! Congratulations, airport!

Don, You might find it interesting that NC cities such as Raleigh, Greensboro, and Fayetteville had 5-10" of snow from this early April of 1915 snowstorm! These are by far the heaviest April snows there on record. A trace even fell at least as far south as Columbia, SC. Many all-time record April low highs (still to this day) were set deep into the SE (including Jacksonville) along with cold rains. Savannah had a high as low as 46 and lows in the upper 30s with rain. Edit: Per meteorologist Eric Webb, this was at the tail end of a moderate El Niño.

Just for the record, I think this model is trolling you: April Fools! But this is really on this crazy model's crazy 6Z run for April 1st following it having record lows in the Dakotas 3/29-31 following it having (near) record lows in S Canada 3/28. The GFS (like is the case for some other models) often overdoes cold lows over snowcover sometimes badly like it probably is doing in this run over the Dakotas and S Canada, which very likely is leading to a colder airmass plunging down from Canada. The next run will probably be much warmer late March through 4/1. But regardless: @dsaurdoes sometimes say to wait til after the Masters before declaring cold to be over. Don't argue with Tony as he knows his SE weather!

Just posted by Wilmington, NC, NWS: UPDATE AN INTERESTING MORNING! ADDED SPRINKLES TO THE FORECAST AREA-WIDE PER RADAR RETURNS FOR THE NEXT HOUR OR TWO. SEVERAL CREDIBLE REPORTS THAT SOME SLEET PELLETS HAVE BEEN MIXING IN AT TIMES. TEMPERATURES GENERALLY WELL ABOVE FREEZING BUT SOME STRONG WET BULB INFLUENCE OBVIOUSLY GOING ON. GIVEN THE SLOWLY RISING TEMPERATURE FELT THIS WOULDN'T BE THE CASE FOR MUCH LONGER ESP AS VIS SAT IMAGERY SHOWS THAT THE WEAK ISENTROPIC LIFT APPEARS TO BE WEAKENING. ------------------------ It makes sense with 850 mb temperatures well below 0C (-3 to -4 C) there. 925s were also sub 0C. Edit: Lows of 36 at KSAV and KSVN, not quite as cold as the 34/35 at KSAV on 3/15 and 3/16, respectively.

These wild swings within a few days are what makes the non-summer and especially winter months much more interesting to me as regards forecasting than the doldrums of summer. KATL ended up with a low above the forecasted high 20s, 31. Tonight should be colder there and in most of the SE, the coldest of the month to date in much of the SE although probably not here and nearby.

For those like myself who enjoy sunny, cool to cold, and low dewpoints for outdoor activities, this is a day to savor, which I'm doing knowing there are very few of these during May-Sep and there almost for sure won't be another near this cold again after this cold spell ends til at least November. I'm especially appreciative of this cold spell knowing 80s should be back here later this week. I had a great walk yesterday evening and look forward to another enjoyable one today. It is now near 60 with breezy conditions, dewpoints in the 20s, and a beautiful deep blue sky that Canadian airmasses often provide along with some pretty cirrus. Meanwhile, wow at how cold it is in the big ATL, what would be cold even for mid January!

After the prior impressive one, the second Canadian airmass is even more impressive in Atlanta. Tomorrow's high is progged to be 45 (with full sunshine!), which would be the coldest since the 45 of way back on January 14! There are 3 freezes on the way, with high 20s forecasted to be the coldest at Hartsfield the next two nights. Anything 28 or lower would be their coldest since 12/26! Let's go! You don't often get -15C at 850 in TN in mid March, but this may occur tomorrow at 12Z. Edit for 3AM at KATL: it is down to 41. But with only 5 more hours of cooling time, I don't know that there will be enough time to get down to the forecasted 28. Actually, 24 hours ago it was already down to 40. But the dewpoint then was still up at 32 vs the current way down to 19. We'll see if KATL makes it as a secondary cold front came through recently and cooling may accelerate with clearing skies. Nashville is now down to 27. Huntsville is 32, Chattanooga is 33, and Rome is 37 (all with clear skies). Regardless, Sun night will probably be colder if it doesn't get to the upper 20s later tonight. Edit: @dsaurI would have loved for you to get a pellet or three but it was way too dry for anything to get to the ground.

Sometimes the CMC typically being the coldest of the models on good radiational cooling nights pays off. But overall, it is well known that this model suffers from a significant cold bias. Regarding today's 12Z, it has low 20s lows in much of the Atlanta suburbs for 3/20 and 3/21 (I'll call it ~21 on 3/20 and ~23 on 3/21) per the Tropical Tidbits maps. What do other models show for 3/20 and 3/21 lows for the Atlanta suburbs? - GFS (12Z) 30 and 35 - ICON (12Z) upper 20s and 35 - UKMET (12Z): upper 20s and low 30s - Euro (0Z): upper 20s and low 30s So, in typical CMC fashion on good radiational nights, it has lows significantly colder than the other major models. On 3/20, it has ~21 vs ~28-30 on the other four. On 3/21, it has ~23 vs ~32-35 on the other four. I'll use the average of the NWS' lows for Marietta, NE Atlanta, and W Atlanta as representation for the average suburb low and see how the models end up doing. For the prior cold snap, the coldest these 3 stations averaged for a low was 28 on 3/15. So, the CMC is calling for this next airmass' coldest to be a whopping 7 colder (on 3/20) than 3/15 vs the other models being about the same on 3/20 as 3/15. I plan to post the verifications regarding 3/20-1 afterward.

Indeed, after the GFS had a good number of runs (in addition to the 12Z 3/15 JMA for 3/19-20 and a couple of teases by the CMC) with a widespread multi-inch SE snowstorm in parts of N GA, NW SC, and much of NC 3/21-2, no model is now showing anything close to a significant wintry threat in the SE. The GFS runs with the most widespread multi-inch snow (they're still on Tropical Tidbits) were these runs: 3/11 6Z, 3/12 12Z, 3/13 6Z, and 3/14 6Z/12Z. Actually, practically all of the GFS runs from 3/10 12Z through 3/15 6Z had multi-inch snow in some non-mountainous locations before abruptly ending that with the 3/15 12Z run.

These last three days of wx have been near ideal for March from my point of view. The walks have been fantastic. The contrast to the very warm and muggy 2/21-3/7 couldn't have been much greater. The dewpoints going way down into the high teens yesterday was awesome. Today's 20s dewpoints along with sunshine and highs in the 60s felt so good. Felt like a pleasantly cool summer day up in the CO Rockies! KSAV had lows of 34 and 35 these last two days, the coldest since way back on January 28th!

Lol and here it may end up helping! It is quite possibly related to the very warm Atlantic. From this same wave 1, the 0Z CMC came very close to wintry precip late Saturday night from C GA to SE NC with rain just meeting the 0C 850 line. There was nothing like that in recent runs as the precip was offshore the SE. So, a big NW shift with this, too!

Check out the 0Z GFS. Stronger wave 1 on this, too, at the expense of wave 2. Of this trend continues, wave 1 could turn out to be the primary, which would be good because the cold air has much less time to modify. Even though the 0Z GFS had no wintry, the precip just missed reaching the 0C 850 in SC before exiting stage right. Look at the trend of recent GFS runs and you'll see the precip from wave 1 getting further NW.

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.