000 acus01 kwns 041253 swody1 Storm Prediction Center ac 041252 Day 1 convective outlook National Weather Service Storm Prediction Center Norman OK 0652 am CST sun Jan 04 2015 Valid 041300z - 051200z ..there is a marginal risk of severe thunderstorms from Florida Panhandle to southeastern Virginia... ... a band of thunderstorms will move across parts of the Florida Panhandle...northern Florida...Georgia...the Carolinas...and perhaps southeastern Virginia today. Isolated damaging winds are possible...and there is a marginal tornado risk. ... In middle-upper levels...broadly cyclonic pattern will prevail over central/eastern Continental U.S. This period. Former 500-mb cyclone now is ejecting northeastward across northern Illinois...and is forecast to accelerate northeastward across southern ont to southern Quebec by 00z. This will occur as trailing shortwave trough -- now evident in moisture-channel imagery over northern OK and southern/eastern Kansas -- pivots eastward across middle south to southern Appalachians. After 00z...vorticity plume associated with latter perturbation will become progressively more deformed NE-SW and weaker in magnitude...as associated trough gets entrained in broader-scale cyclonic flow. At surface...11z analysis showed cold front from surface low over southern ont...south-southwestward across Ohio and eastern Kentucky...and roughly bisecting Alabama from NE-SW. Front was preceded by squall line that now extends from northwestern SC across west-central Georgia to west-central Panhandle of Florida. Ahead of cold front..plex/evolving warm-frontal zone was analyzed from northestern Georgia squall-line intersection northeastward across Piedmont of Carolinas then eastward to northestern NC...while earlier damming front dissipates over central/southeastern Georgia. Warm front should consolidate over central NC and move northward at least through Hampton Roads area before being overtaken by precipitation plume extending northeastward from squall line...and eventually...by cold front itself. Cold front should move offshore most of Atlantic coast except for northern/central Florida by 06z. ..FL Panhandle to southeastern Virginia... Isolated severe is possible...primarily with squall line as it moves eastward across outlook area. Risk has been shifted southwestward in concert with convective trends and expected continuance of favorable warm-sector parameter space. Narrow corridor of rich low-level moisture will advect northeastward...S of warm front...between squall line and pocket of relatively dry air around 850 mb evident on 12z tlh/jax/tbw radiosonde observations. This process...in combination with areas of diffuse surface diabatic heating near east fringe of cloud canopy...should offset stable layers and other areas of weak lapse rates aloft enough to yield at least marginal buoyancy. Modified radiosonde observations and forecast soundings suggest 500-1000 j/kg MLCAPE over most of this area. 50-60-kt effective-shear magnitudes should remain common over squall line for another 6-9 hours before diminishing. A tornado cannot be ruled out either...especially into early afternoon in association with qlcs vortices...before veering of warm-sector flow shrinks and straightens hodographs. With time this afternoon and evening...low-level convergence will weaken as substantial middle-upper-level forcing for ascent remains behind cold front and flow continues to veer in surface warm sector. In tandem with weakening surface-based instability...this will reduce convective intensity and coverage...and likewise close any remaining severe threat. .Edwards/marsh.. 01/04/2015
Posted on: Sun, 04 Jan 2015 13:29:28 +0000
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