SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0745 AM CDT Thu Oct 08 2020 Valid 081300Z - 091200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS IN PARTS OF NEAR-COASTAL SOUTHERN LOUISIANA... ...SUMMARY... A tornado is possible over near-coastal southern Louisiana late overnight. ...Synopsis... In mid/upper levels, the northern-stream pattern is becoming more zonal following the departure of a strong shortwave trough from New England across the Canadian Maritimes. Meanwhile, a vorticity max -- evident in moisture-channel imagery over west-central OK -- is forecast to move slowly northeastward to the OK/KS/MO border area by the end of the period, with trough southwestward across west- central/southwest TX. As that occurs, Hurricane Delta is forecast by NHC to turn northward across the western Gulf this period, toward a mid-period day-2 landfall along the southwestern LA coastline. See latest NHC advisories for specific track/intensity forecasts and tropical watches and warnings related to Delta. ...Southern LA... A tornado may occur the last few hours of the period from outer-fringe convection associated with Hurricane Delta. This is a marginal and conditional outlook predicated on: 1. Latest NHC forecasts of track, speed and expansion of the supportive wind fields, juxtaposed with 2. Most probable outer reach of favorable, discrete to semi- discrete convective modes that could become supercellular amidst enlarging hodographs, and 3. Favorable inland migration of a maritime/tropical boundary layer that, based on modified forecast soundings from several models, would contain theta-e large enough to offset warm temperatures aloft and yield surface-based buoyant parcels. Such conditions are expected to spread well inland and include the diurnal-destabilization period Friday/day-2, but marginally may spread as far north as roughly I-10 by the 12Z ending time of this outlook period. Low-level shear and buoyancy each are expected to diminish with inland extent overnight, even as they gradually increase in an absolute sense at any given spot with Delta's approach. ..Edwards/Goss.. 10/08/2020
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