MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)
Some Questions Remain, But Snowstorm (Starting As Rain) Looms As Increasing Probability For Virginias, Mid-Atlantic Region March 6 - 7
Plymouth State University Weather Server (2)
While there are still a few pertinent questions about the exact track and intensity of the storm digging out of Alberta (and yes, it does technically qualify as an Alberta Clipper), the numerical models seemingly favor a more northward trend, and perhaps a more intense systems as well. I think that the main operational forecast models are somewhat underdone with the strength of the feature, based on the fact that the low center appears to have a good tropical moisture fetch (one already along the West Coast, and an existing axis over the Gulf States). Since the ridging over Quebec is transitory to a split flow (and not a true block). I am expecting the ultimate path of the surface pressure falls to be into lower/middle Appalachia, then east-northeast through the Virginia Capes. Clustering of 700MB vertical velocities would appear to favor the heaviest snowfall to be over SE KY, WV, VA (west of Interstate 95), with a start as rain or extensive mixing with sleet and/or rainfall from NE NC into DE and S NJ.
I would not be surprised to see up to two feet of snow in portions of the Cumberland Plateau eastward into the Shenandoah Valley. Because of the power of the cyclone, some extension of snows could reach as far north as New York City NY and southernmost New England. The complication that bothers me is the lack of a defined cold air input, which only strong vertical motion will be able to compensate for. All in all, the Virginias and much of the Mid-Atlantic region will be paid a visit by winter. Before the milder air returns late week.
Another Case For Unusually Cold Weather In The West (With Thunderstorms And Higher Elevation Snows, Too), As Warmer Air Arrives East Of The Rocky Mountains
There have been some fairly impressive cold snaps across the West this winter, alternating with the "normal" mild and dry days as evidenced in the past week. But the vast storm complex near the Aleutian Islands is likely to dig down into California and the Desert Southwest by later Thursday. Cold air support looks quite strong, so thunderstorms, some severe, may target an area from the Interstate 5 and 105 corridors into the southern Rocky Mountains at the beginning of next weekend. Snow should be heavy as well in many of the higher elevations of the Intermountain Region. Of course, while the western states see a colder turn, southwest flow ahead of the trough complex should produce much milder, bordering on warm, results from the High Plains into the Eastern Seaboard.
EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)
Storm Prediction Center Severe Weather Summaries
Others May Disagree, But Warmer Trends Continue For Much Of U.S. Outside Of West Coast (After A March 9 - 11 Storm Passes)
University Of Nebraska HPRCC
Pennsylvania State University Weather Server
While timing of the slow-moving storm system entering the West this week will be difficult, the most probable scenario is that posed by the ECMWF version, where the closed low is kicked east-northeast by the approach of another disturbance. If this is indeed a progressive feature acquiring a negative tilt and impressive surface convergence, then severe weather and heavy rainfall is possible in a belt from TX....OK....KS through the Old South and possibly the Ohio Valley and Mid-Atlantic region around March 11 - 13. Remember that the potential heavy snowfall would melt, and additional rains would exacerbate flooding problems in portions of the Midwest and Eastern Seaboard visited by frozen precipitation.
There has been a great deal of talk about potential for a cold month of March. Unfortunately, the dynamic models have been predicting blocking signatures which have failed to verify. What appears to be happening in the lower 48 states is typical of spring: large cutoff lows at 500MB in a split, yet progressive, flow pattern. I see no changes in this jet stream configuration through the next month or two, and the prevalence of west/southwest winds to the right of the Continental Divide leads me to believe that the rest of this month will be quite mild, with the warmest anomalies between the Rocky Mountains and Appalachia.
The flat neutral ENSO signal looks to be a keeper through October (after which it may veer into, or close to, weak El Nino territory), so most analogs are favoring a very hot, front loaded (May, June, July with the major heat anomalies in the eastern two-thirds of the nation) summer. The tropical cyclone season looks to be off to a fast start, and probably a prolific one too with potential for multiple (and sometimes intense) warm-core cyclogenesis cases in both oceanic theaters adjacent to North America.
Never a dull moment, eh?
Prepared by Meteorologist LARRY COSGROVE on
Saturday, March 2, 2013 at 8:00 P.M. CT
The previous statements are my opinions only, and should not be construed as definitive fact. Links provided on this newsletter are not affiliated with WEATHERAmerica and the publisher is not responsible for content posted or associated with those sites.
Copyright 2012 by Larry Cosgrove
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