GaWx

This is just digital out 9 days on an operational GFS. Here today gone tomorrow happens very often in these unusual locations. Haven’t seen the real thing in 6 years. Not that digital isn’t fun to see.

Wintry precip way down in my area on 2/18 on 12Z GFS! These sharp changes from run to run show the level of uncertainty. Not all of this is snow as some is other wintry:

Absolutely the 12Z GFS is clearly much better.

The 2/13-20 averaged 0Z 2/9 GEFS predicted AO rose quite a bit to -2.7 (see image below) vs -3.2 on 2/8, -3.0 on 2/7, and -3.5 on 2/6. Also, the PNA is lower while the NAO is higher. So, not good trends at 0Z on the GEFS vs yesterday. Hopefully that trend will reverse as there’s still time. Strongest -AO El Niño averaged 2/13-20 (lowest daily) out of 25 Ninos since 1952: 1969: -4.8 (-5.1) (PNA: -0.1) 2010: -4.4 (-5.1) (PNA: +0.7) 1978: -2.6 (-4.8) (PNA: +0.8) 1958: -2.5 (-4.0) (PNA: +1.1) 1970: -2.4 (-4.0) 1964: -2.4 (-3.4) 1987: -2.4 (-3.3) 1966: -2.2 (-3.5) 1952: -2.1 (-2.5) 1983: -2.0 (-2.7) 1977: -1.2 (-2.1) 2007: -1.2 (-1.9) 2005: -1.1 (-1.7)

Let’s see how 12Z runs go. Not starting off well with the ICON, which has more Pacific flow than recent runs through 144.

The 6Z GEFS was less suppressed with the mean low track and was warmer overall with much less snow throughout the SE and very few (only 3/10%) with wintry into the deep SE. Only one member has wintry in N FL 2/17-21 and that one only barely. That compares with one run that had 10/33% with N FL wintry and a good number with 3-5.

Looking at hour 240 dewpoints and 850s along with the control, it appears that had the Euro gone further that this would likely have resulted in a significant winter storm from a mix for especially NE GA into the W half of NC.

Once again the GEFS mean and GFS are on different planets. The 0Z GEFS is pretty impressive from NE GA through much of NC.

If only the CMC at 222 were remotely credible.

I wish the JMA were a credible model at 192. Edit: 0Z ICON at 162 looks nice.

Even though you’ve never seen it, it has occurred a number of times in GA even in Mar including 3/2-3/1962 in a good portion of inland SOUTH GA (major storm), light icing to the coast on 3/2/1980 (El Nino) and a major one as late as 3/25/1971 in the Atlanta-Athens areas! There was also major icing even to the coast as late as 2/25/1914 (one of their worst ever)(another El Niño)! So, I wouldn’t at all discount the possibility of ice in GA with this next potential threat.

All have BN temps, but none are this cold.

This is the coldest the Euro Weeklies have been in the SE for the week of 2/19-26: dark blue is ~6-7 F BN. That’s pretty significant for an ensemble mean and it could even trend colder. But even if not, a week of 6-7 BN implies the coldest day would probably easily be in the teens or so BN.

Just for the record, the 12Z GFS isn’t the first GFS showing significant wintry somewhere in the SE as most runs over the last few days have shown that. Not always in your BY but somewhere in the SE, sometimes deep south.

Low p8 is about as good a place as any.

The 2/13-20 averaged 0Z 2/8 GEFS predicted AO dropped back some to -3.2 (see image below) vs -3.0 in the 2/7 run and -3.5 in the 2/6 run. Strongest -AO El Niño averaged 2/13-20 (lowest daily) out of 25 Ninos since 1952: 1969: -4.8 (-5.1) (PNA: -0.1) 2010: -4.4 (-5.1) (PNA: +0.7) 1978: -2.6 (-4.8) (PNA: +0.8) 1958: -2.5 (-4.0) (PNA: +1.1) 1970: -2.4 (-4.0) 1964: -2.4 (-3.4) 1987: -2.4 (-3.3) 1966: -2.2 (-3.5) 1952: -2.1 (-2.5) 1983: -2.0 (-2.7) 1977: -1.2 (-2.1) 2007: -1.2 (-1.9) 2005: -1.1 (-1.7)

These MJO forecasts are conducive 2/17+ for a cold SE with low amp 8 followed by going into the left side of the circle:

I’ll need to delete this very shortly because it is a screenshot taking up way too much of my attachment space: note that much of S AL gets 0.75-1” of snowfall in the mean. *Image deleted*

The 6Z GEFS went back colder with an increase in suppressed members and thus an increase again in deep S wintry members, especially from Macon SW to just N of Mobile. Those areas get hit pretty hard by 5 of 30 members. Also, 30% (9) of the 30 have significant and rather widespread IP/ZR in some of the SE. Two of these have a mix in far N FL. A good portion of the deep south wintry is IP/ZR, which doesn’t show up well in snow accumulations. Main period of wintry is within 2/17-21.

Yeah, don’t count your chickens too early. My suspicion that the warmer with further N mean low track would mean less SN in the deep S turned out to be confirmed. Way less there and even less up in ATL-AHN corridor. Whereas N FL had a whopping 10 with wintry on the 18Z, the 0Z has only one! But NE GA to NW SC (to CAE) to the NW 3/5 of NC had an increase due to less suppression.

The 0Z GEFS is significantly warmer than recent runs. Also, mean low track further north. Will that reduce mean snowfall in especially the deep south? Warmest GEFS run in 7 runs. Not what I wanted to see. Still easily far out enough to reverse on near future runs, of course.

OTOH, the 0Z CMC is 25-30 F colder just about everywhere from the SE to the Midwest. What the? The CMC at 240 looks to me like it is set up for a big winter storm to affect at least part of the SE soon after!

Is it my imagination or is the 0Z GFS really looking like dog poop again? Edit: Actually dog poop looks way better!

The 18Z GEFS is easily the best run yet for the SE as a whole. Not only NC does well, but Florence to CAE to Augusta to MCN to Columbus to, believe it or not, far S AL and the FL Panhandle has by far the most snow of any run. Before this run, the largest # of members with FL wintry was 5 (two runs). This run has a whopping 10 in N FL (1/3)! There’s a near 1” mean in the FL Panhandle! This suggests how clueless is the 18Z GFS.

In ATL, record low maximums are in the 30s and 20s through March 18th. Plus you can get significant snow with a high in the 40s. You don’t need mean temps 30-40 BN even in mid March to get a snowstorm. For example, KATL’s heaviest snowfall since 1940, 3/24/1983, was 7.9” and the mean temp was only 18 BN.