SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0228 AM CDT Tue May 04 2021 Valid 061200Z - 071200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THURSDAY ACROSS PARTS OF NORTHERN FLORIDA AND EASTERN PORTIONS OF THE FLORIDA PENINSULA... ...SUMMARY... Strong thunderstorms may impact parts of northern Florida and Atlantic coastal portions of the Florida peninsula Thursday, a few of which may pose at least some risk for large hail and damaging wind gusts. ...Synopsis... While upstream flow over the northern mid-latitude Pacific trends more zonal during this period, models suggest that mid-level ridging and troughing on the leading edge of this regime will remain amplified. Eastward progress of the troughing inland of the Pacific coast, and the ridging across the Rockies, will be slowed, as blocking in the downstream flow (centered near the Labrador Sea) persists. A broad and deep mid-level closed low is forecast to remain centered near James Bay, with troughing to its south amplifying east of the lower Mississippi Valley in response to at least a couple of digging short wave impulses. Models indicate that this will be accompanied by substantive lower/mid tropospheric drying as far south and east as the northern Gulf of Mexico, central portions of the Florida peninsula and the Atlantic waters off the south Atlantic coast by late Thursday night. Destabilization, largely supported by seasonably strong mid-level cooling across parts of the middle Mississippi into lower Ohio and Tennessee Valleys, as well as across parts of the northern U.S. intermountain region, aided by surface heating, may contribute to a risk for thunderstorms during the day. Steepening lapse rates associated with seasonably strong daytime heating may also contribute to some risk for thunderstorms across the southern Rockies, aided by orographic forcing. Seasonably high boundary-layer moisture content will largely be confined to ahead of a surface frontal zone advancing southward into the Florida peninsula. ...Florida... Models suggest that the front, or a pre-frontal convective outflow boundary, initially extending across northern Florida early Thursday, may become a focus for increasing forcing for ascent by early afternoon. It appears that this will be supported by increasingly cyclonic and difluent mid/upper flow, in the presence of modestly steep low-level lapse rates, convective instability and CAPE on the order of 1000+ J/kg. Beneath 30-40+ kt westerly flow in the 700-500 mb layer, the environment might become at least marginally conducive to organized storms capable of producing severe hail and damaging wind gusts. Wind fields will be weaker, but with pronounced veering with height along the sea breeze near or inland of the Atlantic coast, where low-level convergence will become focused Thursday afternoon. In the presence of somewhat steeper low-level lapse rates and larger CAPE, a supercell or two might not be out of the question. Otherwise, stronger storm development may become capable of producing strong downbursts, before diminishing/spreading offshore Thursday evening. ..Kerr.. 05/04/2021
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