SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1152 PM CST Wed Feb 24 2021 Valid 251200Z - 261200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF NORTHERN TEXAS INTO SOUTHERN ARKANSAS...NORTHERN LOUISIANA AND CENTRAL MISSISSIPPI... ...SUMMARY... A couple severe thunderstorms may impact a corridor across north-central Texas through the Ark-La-Tex vicinity tonight, with a couple instances of marginally severe hail or damaging gusts possible. ...Synopsis... Broad cyclonic flow aloft will dominate the upper pattern across the CONUS through today. An embedded mid-level trough will traverse the Southern Plains while a second trough aloft impinges on the Pacific Northwest. Across the southern Plains into portions of the Mid-South, a stable boundary layer will be in place for most of the period. Nonetheless, a 35+ knot 850 mb jet is expected to develop by late afternoon/early evening in response to the approaching upper trough, transporting appreciable moisture northward (evident via 00Z LCH/LIX observed soundings), beneath 6-7 C/km mid-level lapse rates, resulting in up to 500 J/kg MUCAPE across portions of northern TX into central MS in the 21-12Z time frame. Deep-layer ascent will be in place to initiate elevated convection, with an 80 kt 500 mb jet streak overspreading the region beneath the right-entrance region of a 300 mb jet streak. Despite marginal instability, strong deep-layer directional and speed shear may encourage storm organization and longevity, with a couple of strong to briefly severe storms possible. Across the northwest U.S., meager buoyancy preceding the approach of a mid-level trough and associated source of ascent may encourage isolated thunderstorm development to the lee of the Cascades. Elsewhere across the CONUS, cool and stable conditions will serve to mitigate thunderstorm chances. ...Southern Great Plains into the lower Mississippi Valley tonight... Within the 21-00Z period, convective initiation is expected to occur within a warm-air advection regime at the nose of a developing low-level jet. Forecast soundings suggest that the southern Plains storms will remain rooted above 850 mb given the aforementioned stable layer. Mainly small hail is expected to be the main threat with these storms given skinny CAPE profiles as depicted by forecast soundings, however a couple stones over 1 inch in diameter cannot be ruled out given the 60+ knots of effective bulk shear in place to support updraft organization/longevity. By around 06Z, storms tracking east towards Mississippi will encounter a moister low-level airmass as they traverse the 850 mb jet axis. While storms are still expected to be elevated, the availability of deeper moisture suggests that storms may attempt to root closer to the surface, potentially obtaining transient supercellular structure. A couple damaging gusts may accompany the longer-lived, stronger storms that form. ..Squitieri.. 02/25/2021
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