SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1042 PM CST Sun Nov 01 2020 Valid 021200Z - 031200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Aside from portions of the lower Colorado Valley vicinity into the southern Great Basin, the risk for thunderstorms appears negligible across much of the U.S. today through tonight. ...Discussion... Models indicate that broad and amplified large-scale ridging will persist within the westerlies, across the Pacific coast through the Canadian Prairies/U.S. Great Plains and Mississippi Valley through this period, with similar amplitude troughing downstream, across the Atlantic Seaboard into the western Atlantic. A surface cold front associated with the mid/upper troughing is expected to be in the process of advancing south of the Florida Peninsula by early today. Considerable low-level cooling and/or drying will continue to spread southward in its wake, through much of the Gulf of Mexico and well into the western Atlantic. Within the larger-scale ridge, it does appear that the highest mid-level heights (emanating from the subtropical latitudes) will begin to become suppressed across the Intermountain West and Rockies. This is expected to occur as weak smaller-scale troughing, and an embedded cyclonic circulation, are forced inland of the southern California coast, in response to the approach of a splitting short wave trough across the southern mid-latitude and subtropical eastern Pacific. The lead perturbation is forecast to progress into parts of the southern Great Basin and Plateau region by late tonight, preceded by an elevated return flow of moisture emanating from the Gulf of California and lower latitude eastern Pacific. ...Lower Colorado Valley into southern Great Basin... Models suggest that the most substantive moisture return will be near or above the 700 mb level. However, in the presence of modestly steep mid-level lapse rates, it appears that increasing convective and conditional instability will become supportive of occasional, scattered weak thunderstorm activity throughout the period, aided by large-scale forcing for ascent associated with the inland migrating perturbation. ...South Florida and Florida Keys... A low risk for thunderstorm activity may linger near/just southeast of the Keys and southeast Florida coastal areas into the beginning of this forecast period. However, this risk is expected to become increasingly negligible shortly thereafter, with the southward progression of the cold front. ..Kerr.. 11/02/2020
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