SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1107 AM CST Wed Nov 25 2020 Valid 261200Z - 271200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTHEAST TX INTO SOUTHWEST LA EARLY FRIDAY MORNING... ...SUMMARY... Isolated large hail may occur with thunderstorms that develop across parts of southeast Texas and southwest Louisiana, mainly from Thursday night into early Friday morning. ...Southeast States into New England... A mid/upper shortwave trough over the central Appalachians/lower Great Lakes vicinity Thursday morning will develop east/northeast across the Mid-Atlantic and Northeast through Thursday evening. At the surface, a cold front will extend from western NY/PA into central AL and southwestward near the LA/TX Gulf Coast vicinity Thursday morning. The front will not advance much across the Southeast as the upper trough and weakening surface low track well north of the region. In fact, a weak shortwave upper ridge will develop over the south-central states in the wake of the ejecting northeastern upper trough. This will allow for the cold front to become diffuse, and in some places retreat northward as a warm front as a southerly low level flow warm advection regime develops across TX and into the lower MS Valley after 00z. The northern segment of the cold front will shift eastward across New England and the Mid-Atlantic through the afternoon, moving offshore by evening. Showers and isolated thunderstorms are expected near/just ahead of the front from the southern U.S. through much of the Atlantic Coast. However, weak instability and modest shear will limit organized severe potential. ...Southeast TX into Southwest LA... An upper trough will deepen over the western states Thursday, and become increasingly cut-off over the Four Corners by Friday morning. As this occurs, a surface trough is forecast to develop from southwest TX into OK, resulting in increasing southerly return flow across southern/eastern TX and the lower MS Valley by Thursday afternoon. This will allow 60s F surface dewpoints to advance as far north as roughly the I-20 corridor from eastern TX into MS by late in the forecast period ahead of a cold front surging southward across the southern Plains. Forcing for ascent will remain weak across the region, and deterministic as well as ensemble/probabilistic guidance varies, but isolated thunderstorms could develop in this warm advection regime late in the forecast period. If this occurs, increasing southwesterly shear and steep lapse rates atop a near-surface cool layer could support elevated supercells. While this threat is highly conditional on storm development, elevated supercells could produce large hail, mainly across southeast TX into southwest LA early Friday morning. ..Leitman.. 11/25/2020
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