SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1130 PM CDT Fri Oct 30 2020 Valid 311200Z - 011200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Aside from parts of the southern Florida Peninsula, the risk for thunderstorms appears negligible across much of the U.S. today through tonight. ...Discussion... Amplification within the westerlies is underway across the mid-latitude Pacific into western North America, and this appears likely to translate eastward, across the Rockies toward the Atlantic Seaboard, later today through tonight. This includes a building large-scale ridge near the Pacific coast, which may build further while also expanding eastward across the Rockies by late tonight. To the east of the ridging, an intensifying short wave trough is forecast to sharply dig southeastward out of Alberta and Saskatchewan, through the northern U.S. Great Plains and much of the Mississippi Valley by 12Z Sunday. This will be accompanied by another cold front. However, in the wake of recent cold intrusions to the lee of the Rockies, including cold surface ridging still present across much of the eastern U.S. through much of the northwestern Gulf of Mexico, models indicate that pre-frontal moistening will be quite modest to weak. With colder mid-level air also lagging to the northwest of the surface front, this will result in negligible destabilization and risk for thunderstorms. A narrow plume of deep-layered moisture/seasonably high precipitable water is forecast to linger along a weakening remnant frontal zone across the southern Florida Peninsula. This regime likely will include upper 60s to lower 70s surface dew points, which probably will contribute to boundary-layer CAPE in excess of 1000 J/kg with daytime heating. Perhaps aided by weak large-scale forcing for ascent, to the south of a remnant mid-level cyclonic shear axis, this is expected to support a few thunderstorms today. Generally weak lapse rates and weak deep-layer mean flow/shear, among other factors, suggest the potential for severe weather is negligible. ..Kerr/Dean.. 10/31/2020
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