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Monday, July 12, 2021

SPC Jul 12, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0258 PM CDT Mon Jul 12 2021 Valid 122000Z - 131200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF THE NORTHEAST STATES AND ALSO THE FLORIDA PENINSULA... ...SUMMARY... Storms may produce damaging wind gusts this afternoon over parts of Florida and portions of eastern Pennsylvania/northern Maryland and southeast New York. Other thunderstorms with downburst winds will be possible over parts of New Mexico/Arizona/southern Nevada and from the mid-South into the Ohio Valley. ...20Z Update... The western edge of the Marginal Risk has been trimmed across portions of the Mid MS Valley and Southeast, in the wake of stronger convection across these regions. Otherwise, no changes have been made to the outlook. Locally damaging winds remain the primary threat through this evening, especially across portions of the Mid Atlantic/Northeast, portions of Florida, and (on a more localized basis) across portions of the Southwest. See the previous discussion below for more information. ..Dean.. 07/12/2021 .PREV DISCUSSION... /ISSUED 1130 AM CDT Mon Jul 12 2021/ ...Northeast States... Low clouds are mixing out south of a stalled front that currently extends from northern PA through southeast NY. A very moist surface layer with dewpoints in the low 70s F should support up to 2000-2500 J/kg as the boundary layer warms this afternoon. With a weak cap in place, storms are expected to develop along and south of the front and over the higher terrain and spread east through the warm sector. Weak to modest westerly winds aloft with weak vertical shear will support multicells, with storms evolving into line segments and clusters. The stronger storms will become capable of producing locally strong to damaging wind gusts this afternoon. ...Florida... With full sun and a moist boundary layer in place, the atmosphere has already become moderately unstable over the FL Peninsula with 2000 to 3000 J/kg MLCAPE. Storms may intensify over central FL along a northward-advancing outflow boundary as well as along the east coast sea breeze this afternoon, with stronger storms likely along boundary mergers. Multicell clusters capable of locally strong to damaging gusts will be the main threat. See swomcd 1264 for more information. ...Southwest States... Isolated to widely scattered storms are expected to develop over the higher terrain and spread southwest. Given presence of stronger convective inhibition and only weak forcing aloft, there is uncertainty regarding how many storms can survive into the lower deserts across southern AZ where the atmosphere will be more unstable. Nevertheless, given inverted-V profiles, storms that develop this afternoon will become capable of producing downburst winds. ...Ohio Valley... Numerous thunderstorms will develop from the Southeast States into the Ohio Valley within a plume of deep subtropical moisture spreading northward along the eastern periphery of an upper low circulation. Very weak mid-level lapse rates associated with the moist thermodynamic profiles will limit overall updraft strength and storm intensities. Nevertheless, 25-35 kt flow in the 800-500 mb layer and steepening low-level lapse rates suggest a few storms may become capable of producing locally strong to damaging gusts this afternoon. Read more LIVE: spc.noaa.gov
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