SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0637 AM CST Wed Nov 11 2020 Valid 111300Z - 121200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE WESTERN/CENTRAL FLORIDA PENINSULA.... ...SUMMARY... A few tornadoes are possible across parts of Florida mainly northeast through southeast of the center of Tropical Storm Eta. ...Synopsis... In mid/upper levels, broadly cyclonic flow will shift eastward across the western/central CONUS and over the Great Lakes through the period, traversed by a series of shortwaves and vorticity maxima. Weak but broad height falls are expected across the Ohio Valley and the Southeast. As that occurs, T.S. Eta should continue to recurve northward then northeastward toward west-central/ northwest FL. See NHC advisories for latest tropical watches/ warnings and track/intensity guidance on Eta. A surface cold front -- initially over OH, western TN and south TX -- will proceed eastward across most of the Northeast through the period, as well as the central/southern Appalachians and north-central Gulf west of Eta. ...FL... The tornado threat from Eta has increased since the last outlook, and probabilities are being introduced accordingly across the peninsula, except for the southeast and far northern parts. Eta has become a strong tropical storm and may strengthen to a hurricane as it obliquely approaches the west-central/northwest peninsular coastline, based on NHC statements and forecasts. The projected track and wind structure will spread favorable low-level shear/ hodographs from southwestern FL across western/central FL through the period, approximately in step with the translational motion of the cyclone. Ambient deep-tropospheric shear (in the 850-200-mb layer) is forecast to strengthen as well. The main question, especially with northeastward/northward extent tonight, will be instability, so for now potential appears maximized over the 5%/slight area. A few mini-supercells already have been observed the past several hours over FL Bay moving northwestward near the southwest coast. Despite: 1. A dearth of surface and upper-air observations between EYW-SRQ, and 2. Untested validity of topical-cyclone wind fields in middle-inner regions by models like the RAP that feed objective-analysis fields... The presence of such convective behavior itself reveals an outer rim of supportive effective SRH, between the already somewhat favorable VAD wind profiles at the TBW/BYX radars. The potential for more such supercells to develop will shift northeastward with time, and theta-e advection/moisture transport inland across western/central FL may gradually destabilize the boundary layer between heavy-precip areas. Substantial destabilization becomes more uncertain with northeastward/northward extent overnight across central FL toward areas just inland from the Atlantic Coast and roughly north of I-4, because of the offsetting factor of extensive/persistent precip over an antecedent air mass with weak lapse rates aloft and near the surface. ..Edwards/Kerr.. 11/11/2020
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