Supplement To The WEATHERAmerica Newsletter, January 28, 2009

by LarryCosgrove | January 28, 2009 at 05:19 pm

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Major Winter Storm, Intrusion Of Arctic Air, February 1 - 4

Although some may be incredulous at the idea of another "big hitter" storm affecting the U.S., odds on such an event are increasing. The operational GFS version has been extremely consistent with its depiction of a disturbance in the southern branch becoming better organized over the westernmost Gulf of Mexico on Sunday, February 1. With a +PNA ridge complex reforming over the Intermountain Region, a shortwave in the polar westerlies may dig through the Great Plains as the lower latitude feature emerges on the Gulf shoreline of Texas. With the added approach of a small vortex in the Arctic jet stream over western Ontario, the stage may be set for a bombogenesis episode over lower or middle Appalachia on February 2.

Obviously, track considerations come to the fore when we deal with a strong midlatitude cyclone. The standard formats of the 12z GFS and ECMWF schemes were virtually identical with respect to a Piedmont track after an initial route offshore along the Gulf Coast. If those equations verify (about a 1 in 3 possibility at this point in time), then the deepening low will take an inland path just to the right of the spine of the Appalachian Mountains, moving from near Macon GA to Fort Kent ME during a February 1 - 3 timespan. The variants of the GFS version seem to suggest a track offshore near Cape Hatteras, then to bending along the Atlantic Coast into New Brunswick. In between is the European model ensembles, which point toward a trajectory close to the shoreline. This system could be a premier snow maker for parts of the Ohio Valley and lower Great Lakes (maybe, just maybe, breaking Pittsburgh's 2009 snow curse....), while at the same time hammering Appalachia as well as the Shenandoah, Susquehanna, and Hudson Valleys with an ice storm. Barring an eastward shift in the trajectory of the low, it would appear that mainly rain will fall across the Atlantic Coastal Plain.

Climatology for lows that develop over the western Gulf of Mexico show a tendency to pass to the west of the Appalachian Mountains into western Pennsylvania and New York state. Given the rightward bias of the numerical models of late (the ECMWF scheme has gotten the nod on the last two significant systems to reach the Northeast), I suspect that the most likely option is for the disturbance to pass just west of the most recent American and European outlooks. The primary reason we should be looking at a westward drift of the forecast storm track is a simple one: the phasing with the cAk motherlode would act as a "draw", keeping the low on a more northward bent. If merger/phasing were not to occur, the low moving along the Gulf Coast might well head offshore of N FL and GA, with a limited precipitation path that might bring snow or mixed precipitation to cities along the Interstate 95 corridor above Fayetteville NC. Another option, not to be discounted but looking far less likely to happen, would be for a disjointed and weak system to pass across eastern North America with little fanfare.

Strong, But Relatively Brief, Blast Of Frigid Values Across Eastern Half Of The U.S.

With any neutral to negatively tilted storm undergoing rapid deepening, a cold pool over Canada can be tapped and dislocated. This appears to be the case with the February 1 - 3 system, as the numerical models show a strong cAk vortex and aligned trough stretching from Quebec into Florida early in the new week. High winds may accompany the disturbance in its north and west quadrants, accenting chill factors and allowing for quick southward delivery of the Arctic values. Three of the forecast model choices (OpGFS, OpECMWF, GFS ensembles) support a far below normal surface temperature array as far south as the Florida Keys by February 4.