SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0647 AM CST Sun Dec 13 2020 Valid 131300Z - 141200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FAR SOUTHEAST TX/SOUTHWEST LA... ...SUMMARY... Damaging winds and a couple tornadoes are possible across a portion of southeast Texas and southwest Louisiana, mainly from mid-afternoon to early evening. ...Southeast TX to LA and southwest MS... Primary severe potential is expected to peak this afternoon into early evening. Although confidence is not high, the conditional threat for a couple tornadoes and damaging winds appear large enough to warrant a Slight Risk delineation centered on the Lower Sabine Valley. A vigorous shortwave trough over the southern High Plains will move east into the TN Valley by early Monday. Resultant cyclogenesis across the TX Gulf Coast by midday should result in gradual deepening of the low as it tracks from near Houston to Atlanta by 12Z. A richly moist warm sector characterized by 68-71 F surface dew points was present across the northwest Gulf and the Lower TX Coast, supporting a plume of MLCAPE from 500-1500 J/kg, as sampled by the 12Z Corpus Christi and Brownsville soundings. This will probably spread as far northeast as southwest LA. Initially elevated convective development should further blossom across east TX this morning. As forcing for ascent strengthens and low-level warm theta-e advection persists, convective development into the confined warm sector appears possible by mid-afternoon. Enlarged low-level hodographs coinciding with the northeast extent of surface-based instability should support a conditional risk for a couple embedded supercells with the primary hazard being a tornado, centered on the Lower Sabine Valley. Low-level winds are progged to become increasingly veered with southwest extent during the afternoon and a predominant cluster mode early in the convective life cycle should mitigate a greater tornado threat. During the late afternoon to early evening, a narrow squall line should evolve across far southeast TX into northern LA and progress east across most of LA into MS before weakening. Strengthening 700-mb flow behind this line should aid in potential for isolated severe gusts across far southeast TX and southwest LA. Low-level stability will be a limiting factor with northern/eastern extent, but a threat for isolated damaging gusts should exist given the increasingly impressive kinematic profiles. ..Grams/Goss.. 12/13/2020
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