News & Blogs
Southern Winter Storm
By: Drakoen , 10:33 PM GMT on February 19, 2010
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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