Southern Winter Storm

By: Drakoen , 10:33 PM GMT on February 19, 2010

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Winter is certainly not over yet and it appears that the stage is being set for a major winter snowstorm across the South and possibly up into the eastern seaboard. Teleconnections of a negative North Atlantic Oscillation, a sharply negative Artic Oscillation, a positive Pacific-North American Pattern, and negative Eastern Pacific Oscillation favors a deep longwave trough over the eastern two thirds of the country and a large Pacific ridge. 500mb anomalies depict Greenland blocking with anomalously higher heights over Greenland giving way to lower heights over the central and eastern U.S.A. This pattern favors Miller A cyclogenesis; low pressure development in the Gulf of Mexico that tracks up the east coast


The numerical computer forecast models show a longwave trough diving south from the northern section of the country towards the four corners region. The RUC 21z analysis showed the trough axis extending from the Dakotas towards Nevada and the Pacific northwest. A closed 500mb low over the Pacific waters will degenerate into a shortwave trough and round the base on the longwave delivering rain to the Sunbelt region over the weekend in the West and spreading to the Southeast by Monday. The low pressure system associated with the shortwave will track up into the Great Lakes region delivering snow the central and Northern Plains region.


On Tuesday morning the ECMWF, GFS, and GEFS position the longwave trough axis just east of Texas. This southern stream moisture looks to deliver snow to northern and central Texas as the PVA slides eastward throughout the day. Rain should briefly impact the area before snowfall takes over. Interpolated station plots show surface temperatures widely in the mid to lower 30s during the event. 1000mb-500mb charts depict a thickness of 540dm extending down towards the Texas/Mexico border and a deep saturated layer. The GFS shows 850mb temps running between -5 to -8 across central and northern Texas during the snow event and omega values -5 to -10 in the snow growth region around 13,000ft with a complete freezing layer to the surface. The GFS 12z is showing QPF amounts around .25-.5 inches of liquid precip around the Dallas-Forthworth area and south of I-20 and north of Waco .75-1in as the GFS has set up the swath further south. It is too early to determine reasonable snow ratios but, given the mid level dynamics, significant snowfall accumulations could be possible. As the trough slides eastwards snow may stretch into Northern and Central Louisiana, and then potentially on into Mississippi, Alabama, and Georgia.


The GFS and ECMWF shows the southern stream phasing with a polar vortex coming out of Canada. Miller A cyclogenesis begins in the central of eastern Gulf of Mexico on Wednesday or Thursday and the longwave trough tilts negative the low pressure system rapidly races up the coast potentially delivering another snowstorm for the MidAtlantic and Northeast region. It is too early to go into detail about this system but it is worth watching.

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18. Drakoen
3:06 AM GMT on February 21, 2010
Quoting Blizzard92:
Great blog!


Thanks Zachary!
Member Since: October 28, 2006 Posts: 57 Comments: 29928
17. Drakoen
3:05 AM GMT on February 21, 2010
Quoting StSimonsIslandGAGuy:
You think Washington DC area will get heavy snow out of all this Drakoen?


The models no longer show Miller A cyclogenesis in the GOM. It looks like a polar vortex and a secondary low forming off the coast with potential phasing will deliver the punch to the Northeast region. Not seeing anything significant for DC at the moment.
Member Since: October 28, 2006 Posts: 57 Comments: 29928
16. Zachary Labe
3:04 AM GMT on February 21, 2010
Great blog!
Member Since: December 14, 2007 Posts: 282 Comments: 15099
14. Drakoen
5:14 PM GMT on February 20, 2010
Update on the potential winter snow storm:

The latest GFS 12z continues to feature a potent snowstorm for Texas. The model is setting up the heaviest snow in a band south of I-20 around Brownwood and Waco with points around I-20 receiving less snowfall accumulations. Areas around I-10 look to receive light accumulations.

The CMC 00Z and the NAM 12z set up the band of heaviest snow further north along I-20 and point just north. The NAM spits out ligh QPF amounts .25-.5in in the heaviest band and the a sharp cut off for areas south of I-20 near Waco. The CMC is similar to the NAM but slightly more QPF.

After the system passes through Texas Northern and Central portions of Lousiana, Mississippi, and Alabama. The NAM and GFS spits out very light QPF amounts while the CMC suggest another major snowstorm for the south.
Member Since: October 28, 2006 Posts: 57 Comments: 29928
13. Drakoen
4:48 PM GMT on February 20, 2010
Quoting cgmaddog:
Enjoyed the update. Will this affect S Alabama next week?
Mike


The trough that is bringing snow to Texas will slide eastward. The chance for snow will be better over central and northern Alabama. Right now the models are substantial QPF so it is in question as to whether or not there will be enough moisture or if the column will dry up creating virga snow.

Before that trough comes in, the shortwave trough with southern stream moisture will deliver anywhere from an inch to an inch and a half of rain as depicted by the GFS. I feel as though the NAM is too conservative with highest totals up to an inch in locales near the Alabama/Florida border and everywhere else in Alabama less QPF amounts.
Member Since: October 28, 2006 Posts: 57 Comments: 29928
12. Drakoen
4:43 PM GMT on February 20, 2010
Quoting Walshy:
Do you expect anything for western NC next week with snow? Maybe a range? I heard several locals talking about the almanac calling for " the biggest one yet" will occur next week. We have already had 30inches this year which is very unheard off around 2,000FT. The biggest one so far has been 13inches. I just started noticing the local NWS start mentioning it with the recent model runs of the ecmwf. Its hard to believe since this weekend is suppose to be 55-60 with rain Monday and resulting in melting snow! I was trusting that groundhog!



Right now it is too sketchy the models have different solutions. The NAM shows the low pressure system heading eastward out to sea. The GFS keeps the moisture confined further east from you. The ECMWF show more potential for you but not much. Still a wait and see.
Member Since: October 28, 2006 Posts: 57 Comments: 29928
11. Drakoen
4:39 PM GMT on February 20, 2010
Quoting severstorm:
Drakoen,Very well put together forcast. 2 ? How much rain do you think w c fl will get from this and do you see quite a big storm for the eastern seaboard. By the way last time you said i would get .50 to 1in and i got .81. Great call and TIA John


From the first shortwave disturbance .1-.25. From the low pressure system in the GOM, it is very sketchy .25in-.75in possible.
Member Since: October 28, 2006 Posts: 57 Comments: 29928
10. Chicklit
5:17 AM GMT on February 20, 2010
Da bomb.
We could use some rain over here in Fla.
Member Since: July 11, 2006 Posts: 14 Comments: 11186
9. cgmaddog
3:28 AM GMT on February 20, 2010
Enjoyed the update. Will this affect S Alabama next week?
Mike
Member Since: September 24, 2007 Posts: 0 Comments: 38
8. Walshy
2:02 AM GMT on February 20, 2010
thanks in advance
Member Since: May 17, 2009 Posts: 2 Comments: 904
7. Walshy
2:02 AM GMT on February 20, 2010
Do you expect anything for western NC next week with snow? Maybe a range? I heard several locals talking about the almanac calling for " the biggest one yet" will occur next week. We have already had 30inches this year which is very unheard off around 2,000FT. The biggest one so far has been 13inches. I just started noticing the local NWS start mentioning it with the recent model runs of the ecmwf. Its hard to believe since this weekend is suppose to be 55-60 with rain Monday and resulting in melting snow! I was trusting that groundhog!

Member Since: May 17, 2009 Posts: 2 Comments: 904
5. severstorm
12:36 AM GMT on February 20, 2010
Drakoen,Very well put together forcast. 2 ? How much rain do you think w c fl will get from this and do you see quite a big storm for the eastern seaboard. By the way last time you said i would get .50 to 1in and i got .81. Great call and TIA John
Member Since: November 25, 2007 Posts: 0 Comments: 956
4. Drakoen
11:07 PM GMT on February 19, 2010
Quoting hydrus:
Thank you for your post. Here on the Cumberland Plateau, it has been wet and stormy. Last November rainfall was a couple of inches below normal. The remaining months have been above average precipitation. I was wondering what your outlook is for March and April and how much severe weather we will see. If the flow is zonal, I believe it should not be that bad. But if if we have all those huge dips in the jet, We may have tornadoes and squall lines to deal with. jmo


According to the climate models, March looks to be anomalously drier for the eastern section of the country. Around you area shold see average rainfall. Teleconnections shows a slightly negative NAO and a positive PNA into March. We should see less zonal flow and of a trough set up. April looks to be good with anomalously higher precipitation and based on that probably more active weather.
Member Since: October 28, 2006 Posts: 57 Comments: 29928
3. hydrus
10:57 PM GMT on February 19, 2010
Thank you for your post. Here on the Cumberland Plateau, it has been wet and stormy. Last November rainfall was a couple of inches below normal. The remaining months have been above average precipitation. I was wondering what your outlook is for March and April and how much severe weather we will see. If the flow is zonal, I believe it should not be that bad. But if if we have all those huge dips in the jet, We may have tornadoes and squall lines to deal with. jmo P.S.- 54 degree,s here today with still quite a bit of snow on the ground!
Member Since: September 27, 2007 Posts: 1 Comments: 20539
2. Drakoen
10:46 PM GMT on February 19, 2010
Quoting Bordonaro:
Excellent analysis Drak. What is your currest estimate for snow accumulation for N Central TX (DFW, TX are)? My guesstimate is for 4-6" of wet heavy snow.


Around the same as you are. Tough to call though since the GFS dumps different liquid QPF amounts on every run.
Member Since: October 28, 2006 Posts: 57 Comments: 29928
1. Bordonaro
10:43 PM GMT on February 19, 2010
Excellent analysis Drak. What is your currest estimate for snow accumulation for N Central TX (DFW, TX are)? My guesstimate is for 4-6" of wet heavy snow.
Member Since: August 25, 2009 Posts: 20 Comments: 6785

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