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Cheeznado

Post Arctic front snow Tuesday, Jan 29

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Two runs in a row of the NAM show a very sharp drop in temps and some pretty good snow rates- 1-2" in 3 hours or less. 2M temps fall sharply to 26 by 18Z. This is similar to an event on Jan 26, 1985 where we got an inch or so just behind a strong front.

1421437110_ScreenShot2019-01-26at10_02_24AM.thumb.png.33649c979f7a4208b52078ee3741fd0b.png

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I've been watching this for several days.  Models have been somewhat consistent on something for Tuesday.

I read back on January 1985 and it looks like a few days prior 1/21-1/22 there was artic air with very low temps (-8 in ATL).  I'm sure the cold temps helped that scenario.  Some of the models show a rain/snow transition for Tuesday.  What is everyone's thoughts on this?  Will the early precip shown be mostly virga with a dry column? The very cold air behind worries me too.  Could we have an ice under snow situation like 2014?

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Was trying to figure out the forcing mechanisms that make this frontal passage through the southeastern states and associated precipitation different than our usual "cold chasing rain" scenario.

Here is a helpful link describing the anafront scenario. https://www.accuweather.com/en/weather-news/what-are-ana-and-kata-fronts/73473

Looks like the difference is the velocity of the cold at the surface is so fast that it shoots out ahead, with the attendant moisture being forced up and over the advancing cold.

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1 hour ago, Cheeznado said:

Two runs in a row of the NAM show a very sharp drop in temps and some pretty good snow rates- 1-2" in 3 hours or less. 2M temps fall sharply to 26 by 18Z. This is similar to an event on Jan 26, 1985 where we got an inch or so just behind a strong front.

1421437110_ScreenShot2019-01-26at10_02_24AM.thumb.png.33649c979f7a4208b52078ee3741fd0b.png

The GFS made an attempt to move that way.  Oddly enough the GFS 3 days ago looked the best of any model for this event and go figure it’s looked the lousiest the last day or so along with the GGEM.  The closest analog showing is 12/19/00.  It appears to me that east and southeast sides of Atlanta got 2-3 inches with it but oddly enough west of there got hardly anything  

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UKMET seems to be more progressive than the Euro at 72 than the 00z Euro at 84 or the 06Z Euro at 78.  It continues the theme of this winter where the UKMET and Euro generally have not agreed which is rare.  The UKMET has generally lost those battles.  That said the UKMET may still be snowier for many people than the GFS and certainly the GGEM 

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The euro has been increasingly interesting for the Triad and N&W areas of the Triangle. The last run, the kuchera maps had 3-4” from about Asheboro to Durham and areas to the NW.

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The key for my neck of the woods seems to be that precip that blossoms in southern LA and winds it’s way through MS/AL/GA and doesn’t get eaten up by the mountains. 

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3 minutes ago, Queencitywx said:

The key for my neck of the woods seems to be that precip that blossoms in southern LA and winds it’s way through MS/AL/GA and doesn’t get eaten up by the mountains. 

The ensemble members and the NAM and EURO dig things enough so that the front is clearing almost entirely in advance of all the precipitation in many areas.  It’s entirely possible both models are not snowy enough across the Gulf states because at this range even the higher res NAM and Euro tend to underestimate low level bleeding of cold air.  The few hours places like BHM or ATL show rain basically everything but 940mb and down is below 0C.  Very possible that would end up colder if you took the NAM/Euro solutions and played them out exactly 

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Supposedly we dont go above freezing from Tues night until mid day Friday in the Triad.  So this could be fun (annoying) with even minimal QPF.  

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11 minutes ago, kvegas-wx said:

Supposedly we dont go above freezing from Tues night until mid day Friday in the Triad.  So this could be fun (annoying) with even minimal QPF.  

Euro has upper 30s/40 for high Wednesday and 40s Friday with a warm weekend 

 

Edit: Only Thursday has highs below freezing for NC 

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30 minutes ago, wncsnow said:

Euro has upper 30s/40 for high Wednesday and 40s Friday with a warm weekend 

 

Edit: Only Thursday has highs below freezing for NC 

A flash freeze will happen Tuesday evening regardless if it rains or snows. Will be especially dangerous as this occurs around rush hour for I77 and west 

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5 minutes ago, SnowGoose69 said:

ATL just got NAM'd on the 18Z run... .30 snow

Yep. Still plenty of time for that to end up almost all rain of course.

prec.png

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4 minutes ago, SnowGoose69 said:

ATL just got NAM'd on the 18Z run... .30 snow

 

It's literally looks almost like the 2000 analogy you were saying earlier. East and Southeast sides gets lollipopped....west parts of the metro get shafted. Still, it's the NAM.

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Just now, LovingGulfLows said:

 

It's literally looks almost like the 2000 analogy you were saying earlier. East and Southeast sides gets lollipopped....west parts of the metro get shafted. Still, it's the NAM.

The Euro only showed .07 but its very possible the algorithm at this range is not seeing how fast the BL cools...if you look at BUFKIT soundings for the 12Z NAM and GFS they show the FROPA through the metro down there about 15-16Z, The Euro is about the same...and then it drops temps 10 or more degrees in an hour.  If thats the case I think you see more snow than the Euro spat out verbatim

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17 minutes ago, LovingGulfLows said:

18z GFS very interesting for GA at hour 72.

 

gfs_mslp_pcpn_frzn_seus_12.png

 

It tried moving towards the wave idea the NAM showed with the surface reflection

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With that lift, you could certainly see a situation where thunderstorms accompany the ptype change. 

nam_namer_078_700_rh_ht.gif

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From RAH:

The next chance of precipitation will arrive on Tuesday, as the strong Arctic vortex diving south out of Canada absorbs/merges with a lead shortwave trough moving into the southern/central Appalachians. Associated synoptic scale height falls on the order of 60 to 90 meter, in tandem with the attendant Arctic cold front will support an area/band of showers moving east through the area Tuesday afternoon. Models still show the potential that the band of rain showers could briefly change over to snow showers before the moisture departs Tuesday evening/night as colder air pours into the region. This classic cold air chasing the moisture scenario rarely results in significant/warning criteria snow fall for central NC. Will continue to closely monitor. With liquid equivalent of one to two tenths and temps falling quickly into the 20s Tuesday night, the greatest threat/concern could end up being the development of black ice from the flash freezing of moisture on roads, sidewalks and elevated surfaces. Lows Tuesday night ranging from near 20 north to mid 20s south.

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