SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1149 PM CST Wed Nov 25 2020 Valid 261200Z - 271200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF FAR EASTERN TEXAS INTO LOUISIANA... ...SUMMARY... Isolated large hail may occur with thunderstorms that develop across parts of far eastern Texas into Louisiana tonight into early Friday morning. ...Synopsis... A compact mid-level shortwave trough will move across the Northeast and eject into the Atlantic while modest surface lee troughing will prevail along the East Coast through the day into early Friday morning. Adequate moisture and lift associated with this lee troughing will promote at least isolated thunderstorm development. Meanwhile, a second trough aloft is poised to traverse the Inter-mountain West while diverging from the broader upper cyclonic flow regime and evolving into a 500 mb cutoff-low. At the surface, a cold front will move across the Plains states, preceded by a region of weak low pressure and associated low-level WAA across the mid-South. Colder mid-level temperatures associated with the approaching upper trough/cyclonic flow regime will contribute to enough buoyancy to support a very isolated severe threat early Friday morning. ...Portions of the mid Atlantic into the Carolinas... As the aforementioned trough moves toward the Atlantic, a gradual veering and weakening of the tropospheric wind profiles is likely. Marginal instability will be in place to support isolated to potentially scattered thunderstorm development, with strong enough diurnal heating likely to promote some boundary-layer mixing. However, the lack of both stronger buoyancy and flow aloft to be transported to the surface suggests that severe gusts would be too sparse for Marginal highlights at this time. Nonetheless, a strong to marginally severe gust or two cannot be completely ruled out. ...Far eastern Texas into Louisiana... Within the roughly 06-12Z time frame, a plume of steeper mid-level lapse rates (up to 8 C/km based on 00Z NAM, GFS, and 03Z RAP forecast soundings) is expected to overspread a modest moist/warm-air advection regime, promoting over 1000 J/kg MUCAPE in spots. While much of this instability is expected to be elevated, cellular convection may ingest air-parcels down to 850 mb, within a layer of modestly veering low-level winds, with around 150 m2/s2 effective SRH available to any storms that form. As such, storms may become organized and long-lived enough to support isolated large hail, with a Marginal risk for severe storms maintained over the area. ..Squitieri.. 11/26/2020
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