Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1233 AM CDT Mon May 01 2017 Valid 011200Z - 021200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON INTO THE EVENING ACROSS MUCH OF THE LOWER GREAT LAKES REGION...THE UPPER OHIO VALLEY AND THE CENTRAL APPALACHIANS INTO MID ATLANTIC COAST.... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK AREA...AS FAR SOUTH AT THE SOUTHERN MID ATLANTIC COAST REGION... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE SLIGHT RISK AREA...AS FAR SOUTH AS NORTHERN FLORIDA... ...SUMMARY... Thunderstorms are expected to develop and overspread much of the lower Great Lakes region, the upper Ohio Valley and central Appalachians into the Mid Atlantic region today, accompanied by potentially damaging wind gusts and the risk for a few tornadoes. ...Synopsis... Ridging within the mid-latitude westerlies, centered off both the Pacific and Atlantic coasts, may maintain amplitude during this period, but troughing in between may broaden across much of the interior U.S., as a significant embedded short wave trough continues lifting northeastward out of the Plains/Mississippi Valley region. This latter feature will be accompanied by a deep lower/mid tropospheric cyclone which is forecast to track across and northeast of the Great Lakes region by 12Z Tuesday, with an associated cold front advancing into and across the Appalachians and much of the Atlantic Seaboard. As one smaller scale impulse continues pivoting around the eastern and northeastern periphery of the mid-level cyclone, and another digs to its west and south, models suggest that the short wave trough will gradually transition from a negative to positive tilt centered over the Great Lakes by the end of the period. And the mid-level cold core will continue to considerably lag to the west of the warm sector of the occluding surface cyclone. However, substantial strengthening of deep layer wind fields appears likely today within the warm sector, across much of the Atlantic Seaboard by late afternoon. This is where forcing for ascent is expected to support considerable thunderstorm development, which will probably be accompanied by potentially damaging wind gusts, and perhaps a few tornadoes. ...Eastern states... Models indicate strengthening of warm sector 850-500 mb wind fields to 40-70+ kt during the day today, particularly across the lower Great Lakes region, the upper Ohio Valley and the central Appalachians into the northern Mid Atlantic Coast region. This should prove more than favorable for organized severe thunderstorm development, given at least weak boundary layer destabilization, and surface dew points in the 60s probably will contribute to this with daytime heating, despite relatively warm and initially capping mid-level layers. Beneath increasingly difluent flow aloft, frontal and orographic forcing for ascent are expected to aid initiation of thunderstorms near/east of Lake Erie, southward along the western slopes of central into southern Appalachians by 18-21Z. This activity seems likely to eventually consolidate and grow upscale into an organizing squall line as it crosses the Allegheny mountains and plateau, and to the lee of the Blue Ridge, by early evening. As it does, it probably will be accompanied by increasing potential for damaging surface gusts, given the strength of the ambient wind fields, with damaging straight line winds becoming the predominant severe threat. However, supercell structures, within and perhaps ahead of the line as it evolves, may be accompanied by a risk for tornadoes, one or two of which could be strong. Strong/severe storms may reach the Champlain/Hudson Valleys and Mid Atlantic coastal areas by this evening, before weakening within a more stable environment. ..Kerr.. 05/01/2017Read more
from SPC Forecast Products http://ift.tt/s7Jkvo
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