SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1100 PM CST Sun Feb 21 2021 Valid 231200Z - 241200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Aside from the Columbia Plateau vicinity of the Northwest, the risk for thunderstorms appears negligible across much of the U.S., Tuesday through Tuesday night. ...Discussion... Models indicate that a blocking mid-level ridge centered over the southern mid-latitude eastern Pacific will maintain strength through this period, even as a significant short wave impulse within the westerlies begins to progress around its northwestern periphery. Short wave ridging ahead of the perturbation, and to the north-northeast of the ridging, appears likely to shift eastward into the western Canadian provinces and Pacific Northwest. As it does, it may begin to impinge on the southwestern periphery of a deep mid-level low initially centered across the Arctic latitudes, which may begin to gradually shift east-southeastward toward the northern Hudson Bay vicinity. Farther south, inland of the Pacific Northwest coast, mid-level flow is forecast to split, with the western of a pair of inland migrating short wave perturbations taking a sharper south-southeastward turn to the lee of the Cascades. Larger-scale flow, in general, across much of the Intermountain West through the Mississippi Valley is forecast to trend broadly cyclonic, with low amplitude downstream ridging overspreading the Ohio Valley and Mid Atlantic states, in the wake of large-scale troughing rapidly progressing east of the Atlantic Seaboard. While a cold front associated with the lead troughing may progress through much of the remainder of the southeastern Gulf of Mexico and Florida Peninsula, accompanied by low-level cooling and drying, a moistening return flow may continue to slowly develop across the southwestern Gulf of Mexico. Modest low-level moistening (including mid 50s to lower 60s surface dew points) appears possible as far northwest as Deep South Texas, and perhaps the Hill Country/Edwards Plateau vicinity. However, models indicate that this will be capped by a deep, warm and dry lower/mid tropospheric layer. ...Northern Intermountain West/Rockies... In association with the evolving large-scale pattern, models indicate that a large pocket of cold mid-level air (-35 to -40C at 500 mb) will begin to shift southeastward through much of interior North America. By Tuesday, this likely will include much of the northern intermountain region and northern Rockies, where it may support weak boundary-layer destabilization and convective development during the day with daytime heating. While thermodynamic profiles may be mostly below freezing, it is possible that some of this activity could become capable of producing lightning. This potential may become maximized across the Columbia Plateau vicinity Tuesday afternoon, aided by forcing associated with the impulse digging to the lee of the Cascades. ..Kerr.. 02/22/2021
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