SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1050 AM CST Wed Nov 18 2020 Valid 191200Z - 201200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Aside from portions of the Pacific Northwest coast vicinity, the risk for thunderstorms appears negligible across much of the U.S. Thursday through Thursday night. ...Synopsis... Models indicate that the westerlies will trend less amplified across the Pacific coast through the Atlantic Seaboard during this period. Persistent large-scale mid-level troughing near the British Columbia/Pacific Northwest coast is forecast to break down, with perhaps the most significant remnant perturbation accelerating east of the northern Rockies through northwestern Ontario and the upper Great Lakes region by 12Z Friday. Downstream large-scale troughing appears likely to gradually recede to higher latitudes while continuing to shift away from the Atlantic coast. In lower levels, however, the southwestern flank of cold surface ridging has maintained a considerable influence across much of the Gulf of Mexico and Gulf Coast/Southeast vicinity. Models suggest that boundary-layer recovery over the Gulf of Mexico, and the development of a southerly inland return flow, will continue to be hampered by lingering surface ridging through this period. Particularly east of the Rockies, this will continue to contribute to generally dry and/or stable conditions with negligible risk for thunderstorms. ...Pacific Northwest... Models continue to indicate that mid-level height rises will be underway, and the mid-level thermal trough axis (-32 to -34 C at 500 mb) may be in the process of shifting east of the Cascades by 12Z Thursday. However, guidance indicates that the western edge of the cold core (AOB -30C at 500 mb) will linger west of the Cascades into at least Thursday afternoon, while deep-layer flow also remains at least broadly cyclonic. Perhaps aided by large-scale ascent associated with a weak embedded, inland migrating perturbation, modest westerly low-level onshore/upslope flow, and destabilization associated with insolation, a few weak thunderstorms appear possible to the west of the Cascades Thursday. ..Kerr.. 11/18/2020
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