SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1138 PM CST Mon Nov 09 2020 Valid 101200Z - 111200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF NORTHEAST MO...EASTERN IA...NORTHERN IL AND SOUTHERN WI... ...SUMMARY... Thunderstorms capable of producing isolated strong to locally damaging winds and perhaps a few tornadoes are possible this afternoon and evening across portions of the Middle Mississippi Valley vicinity. ...Mid-Mississippi Valley Vicinity... A potent midlevel shortwave trough will become negatively tilted today as it ejects east/northeast from northern/central Plains to the upper Great Lakes. At the surface, low pressure will deepen at it track northeast from MO into eastern IA by midday. Strong southerly flow ahead of the surface low and eastward-advancing cold front will transport low 60s dewpoints as far north as southern WI and southern lower MI. While heating will be limited by cloudy skies, cooling aloft will result in steepening midlevel lapse rates and modest instability (generally less than 750 J/kg MLCAPE) is expected during the afternoon and early evening. Thunderstorms are first expected to develop and intensify during the afternoon across northern MO into eastern IA. Deep layer flow will generally be parallel to the cold front, supporting a more linear storm-mode with line segments/QLCS development expected. Given the deepening surface low, some backing of near-surface winds is expected closer to the low from eastern IA into northern IL and southern WI. This could increase the potential for mesovortex formation within the broader QLCS/bowing segments. Forecast soundings indeed show enlarged, curved hodographs with both increasing directional and speed shear leading to 0-1 km SRH values greater than 250 m2/s2. As a result, a few tornadoes are possible, in addition to isolated strong/locally damaging wind gusts. The severe threat should decrease with time and eastward extent as the boundary layer stabilizes with the loss of daytime heating and strong forcing ejects northeast over the upper Great Lakes and Ontario. ...Florida... Strong deep layer easterly flow on the eastern periphery of Tropical Storm Eta will maintain a moist airmass over the region. Heating through cloud breaks will allow for some destabilization of the airmass over the Peninsula, but poor lapse rates and weak effective shear will limit storm organization. While a couple of storms could produce gusty winds, convection is expected to remain sub-severe. ..Leitman.. 11/10/2020
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