SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1127 AM CST Thu Dec 31 2020 Valid 011200Z - 021200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF THE MID SOUTH AND SOUTHEAST... ...SUMMARY... Thunderstorms associated with isolated severe wind gusts and a marginal tornado threat will be possible on Friday from the Florida Panhandle northward to the Ohio Valley and northeastward into South Carolina. ...Synopsis... Split flow aloft will persist across the U.S. Friday. An upper low in the southern stream -- initially forecast over Oklahoma -- will shift quickly northeastward into the Midwest with time, gradually becoming re-absorbed into the northern stream of westerlies through the end of the period. Meanwhile, a second low in the southern stream -- initially over northwestern Mexico -- will progress steadily east-northeastward into the southern Plains through the period. At the surface, a low over the eastern Oklahoma/Arkansas vicinity Friday morning will move northeastward across the Ozarks through the day, and then continue northeastward through the evening and overnight, reaching the Lower Great Lakes Saturday morning. A cold front trailing from this low is forecast to advance slowly eastward across the central Gulf Coast states/Mid South region through the first half of the period, and then approach/reach the central and southern Appalachian crest by the end of the period. East of the mountains, a cold air dam/wedge front lying across northern Georgia and South Carolina will linger in place through the day, before weakening overnight as low-level southerly flow evolves across the East Coast states ahead of the advancing cold front. ...Kentucky/Tennessee south to the Florida Panhandle... Showers and isolated thunderstorms are forecast to be ongoing at the start of the period, from near the Missouri/Illinois border south-southeast across western Tennessee and into eastern Mississippi/western Alabama, in the vicinity of the cold front. Ahead of the front, weak lapse rates and widespread cloud cover -- plus scattered, warm-advection-induced convection will substantially limit warm-sector instability. Still, favorably strong deep-layer flow, and veering in the low-level wind field -- particularly with northward extent -- will support potential for a few organized/rotating storms. While severe potential should remain subdued given the thermodynamic deficiencies, a couple of locally damaging gusts, or a tornado or two, cannot be ruled out. ...Georgia and South Carolina vicinity... Showers and scattered thunderstorms are forecast to be ongoing over portions of the area at the start of the period, and will persist through the afternoon and into the evening, within a persistent zone of warm advection ahead of the cold front. Given weak lapse rates and widespread precipitation and associated cloud cover, minimal destabilization potential is noted. Still, with strong deep-layer flow across the region, a few stronger storms -- capable of gusty winds possibly nearing or reaching severe levels, may occur. In addition, limited potential for a tornado or two may also evolve, perhaps greatest near the remnant wedge front where low-level vorticity would be maximized. Severe risk will eventually diminish into the overnight hours, as weak short-wave ridging -- and associated large-scale subsidence/warming aloft evolves across the Southeast through the end of the period. ..Goss.. 12/31/2020
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