SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1150 PM CST Sun Nov 29 2020 Valid 301200Z - 011200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE EASTERN CAROLINAS INTO SOUTHERN NEW ENGLAND... ...SUMMARY... Isolated strong to severe thunderstorms capable of producing damaging winds and a couple of tornadoes will be possible today from parts of Florida into the Carolinas, Mid-Atlantic and southern New England. ...Synopsis... Remnants of an upper low crossing the southern Appalachians region early in the period will continue to be absorbed by a sharp northern-stream trough, progged to be crossing the upper Great Lakes/Mississippi Valley at the start of the period. As this trough advances, and fully ingests the remnant upper low, the trough is expected to gradually close off and become its own large upper cyclone -- which will reach the central Appalachians area by the end of the period. As the upper flow field evolves, a deepening surface low crossing western North Carolina/Virginia early in the period will move quickly northward, reaching central New York by 01/00Z where it will then begin to occlude. The trailing cold front associated with the low will move across the Atlantic Coast states through the day, likely clearing the coast from the Mid Atlantic region to Florida through the evening, while a warm sector lingers onshore over southern New England into the overnight hours. ...Eastern Carolinas to southern New England... Widespread showers and embedded thunderstorms are forecast to be ongoing at the start of the period over the eastern U.S., with the main band of frontal convection stretching from West Virginia/western Virginia to the Florida Peninsula early. Limited/local severe potential will be ongoing, with a gradual, modest increase in threat expected through late morning/early afternoon from eastern North Carolina northward into the Mid Atlantic region as at least 500 J/kg mixed-layer CAPE spreads northward across the coastal Mid-Atlantic/Chesapeake Bay region. Very strong flow through a deep layer suggests potential for damaging winds, where stronger storms can transport momentum downward. Meanwhile, favorably increasing/veering flow with height through the lower troposphere will also support potential for low-level rotation -- and thus a couple of tornadoes appear possible where sustained supercell storms can evolve. By mid evening, convection will have largely moved off the Mid Atlantic Coast, while some severe risk lingers over southern New England -- possibly into the overnight hours. ...Central Florida... As the cold front shifts southeastward across Florida through the day, a band of showers and thunderstorms is likewise forecast to cross the Peninsula. Storms will likely be ongoing within this frontal band at the start of the period, but modest CAPE expected ahead of the front suggests that most of the convection should remain sub-severe. Still, with amply strong (around 50 kt) mid-level westerly flow atop the frontal zone, gusty/locally damaging winds may occur with one or two of the strongest storms, before convection weakens into the afternoon hours in the wake of the passage of a weak vort max. ..Goss/Moore.. 11/30/2020
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