Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0744 AM CDT Wed Apr 05 2017 Valid 051300Z - 061200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS THROUGH LATE EVENING FROM EASTERN ALABAMA ACROSS MUCH OF GEORGIA TO WEST CENTRAL SOUTH CAROLINA...AND NORTHWARD ACROSS EASTERN TENNESSEE TO SOUTH CENTRAL KENTUCKY... ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS SURROUNDING THE MODERATE RISK AREA...FROM THE OHIO VALLEY TO THE CAROLINAS AND NORTHEAST GULF COAST... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK AREA... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE SLIGHT RISK AREA... ...SUMMARY... An outbreak of severe thunderstorms with a few strong tornadoes, very large hail, and damaging winds is expected today into tonight from Alabama and Georgia into South Carolina, as well as northward into middle and eastern Tennessee and central Kentucky. ...An outbreak of severe thunderstorms expected today into tonight... ...Synopsis... A surface cyclone in south central MO this morning will develop east-northeastward to southern IN by this evening and northern OH by 06/12z, in advance of an amplifying midlevel trough now over the Ozarks. An embedded shortwave trough/jet streak will rotate around the southern periphery of the midlevel trough, from northwest TX this morning to the lower MS Valley this evening and the southern Appalachians overnight, which will eventually foster secondary cyclogenesis in VA. A trailing surface cold front will likewise progress eastward to middle TN and central AL by late evening, and continue eastward to the Piedmont and northeast Gulf coast by the end of the period. In advance of the cold front, a maritime tropical air mass is spreading northward across MS/AL/GA, which will contribute to substantial destabilization and relatively widespread severe thunderstorm development today into tonight across the Southeast, and this afternoon/evening into the OH Valley. http://...MS/AL/GA/Carolinas through tonight... Elevated thunderstorms have been ongoing much of the night and continue to spread east-northeastward across central AL/GA in a warm-advection regime on the edge of the returning tropical moisture. Embedded supercells are expected to persist into the day, with an increasing risk for surface-based supercell development on the southern fringe of the ongoing cluster as the low levels destabilize with surface heating, as well as in the open warm sector in central/southern AL. The combination of moderate-strong buoyancy (MLCAPE 2000-3000 J/kg), effective bulk shear of 55-70 kt will support multiple supercells capable of producing isolated very large hail and damaging winds. Long, straight hodographs will characterize the wind profiles, with only modest low-level hodograph curvature expected along a branch of the 40-50 kt southwesterly low-level jet across GA. Still, the strong buoyancy and effective SRH in excess of 200 m2/s2 will be sufficient for the risk of a few strong tornadoes mainly across eastern AL, GA and west central SC through the afternoon/evening. Tonight, the southern extent of the cold-frontal severe storms will move eastward from AL into GA, potentially moving along the same corridor affecting by storms during the day. Some form of this convection will move across GA/SC and possibly into NC overnight, with all severe hazards possible. ...OH/TN Valleys this afternoon/evening... An increase in low-level moisture will occur today from TN northward to the lower OH Valley, in advance of the surface cyclone/cold front and west of the ongoing convection across AL/GA. Some surface heating will occur ahead of the front per morning satellite imagery, which combined with the moistening, will result in a corridor of moderate buoyancy extending northward from northern AL across middle TN into central KY, and perhaps southern IN. Convective initiation is expected along or just ahead of the front by mid afternoon, with sufficient cross-boundary flow/shear for discrete storms to move off the boundary. Deep-layer vertical shear and buoyancy will favor supercells capable of producing large hail and damaging winds, while a branch of the low-level jet across TN/KY will provide sufficient low-level shear for isolated strong tornadoes from about 21-02z. ..Thompson/Cohen.. 04/05/2017Read more
from SPC Forecast Products http://ift.tt/rATNzD
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