SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0140 AM CST Sun Feb 21 2021 Valid 231200Z - 241200Z ...NO THUNDERSTORM AREAS FORECAST... ...SUMMARY... The risk for thunderstorms appears negligible across the U.S., Tuesday through Tuesday night. ...Discussion... The area of lowest mid-level heights over the Arctic, initially to the north of Alaska and the Canadian Yukon and Northwest Territories, may slowly begin to shift east-southeastward during this period. Otherwise, models indicate that a fairly prominent, blocking mid-level ridge will persist across the southern mid-latitude eastern Pacific. Within the stronger, broadly anticyclonic westerlies between these two features, a number of short wave troughs will remain progressive across the northeastern Pacific into British Columbia and the Pacific Northwest. In association with the perturbations progressing inland, it appears that flow will trend broadly cyclonic across the Intermountain West into the Mississippi Valley, while downstream flow trends broadly anticyclonic into the northern and mid Atlantic Seaboard, in the wake of large-scale troughing rapidly progressing offshore into the western Atlantic. These developments will be accompanied by further low-level cooling and drying across the northeastern Gulf of Mexico and the south Atlantic Seaboard, including the Florida Peninsula. Although a southerly return flow may develop across the western Gulf of Mexico into the northwest Gulf coast region, it still appears that low-level moistening will be quite modest due to slow boundary-layer recovery in the wake of the recent Arctic intrusion. ...Northern Rockies vicinity... Insolation beneath the western periphery of a broad pocket of cold mid-level air (including -35 to -40C around 500 mb) may contribute to weak boundary-layer based CAPE and scattered convective development Tuesday afternoon, although thermodynamic profiles probably will be mostly below freezing. It might not be out of the question that some of this activity could become capable of producing lightning, but it seems mostly likely that any such occurrences will be sparse in coverage and short-lived, and thunderstorm probabilities appear less than 10 percent. ...South Florida... Prior to the passage of the cold front, there appears some risk for isolated thunderstorm development near southeast coastal areas, though probabilities exceeding 10 percent may be mostly over the coastal waters. ..Kerr.. 02/21/2021
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