000 acus01 kwns 251233 swody1 Storm Prediction Center ac 251231 Day 1 convective outlook National Weather Service Storm Prediction Center Norman OK 0631 am CST sun Jan 25 2015 Valid 251300z - 261200z ..no severe thunderstorm areas forecast... ... isolated thunderstorms may occur across portions of the middle south and Tennessee Valley regions this afternoon and early evening. ... Highly amplified upper-air pattern is forecast this period...with broadly cyclonic flow and troughing over eastern Continental U.S.. meanwhile...ridging will prevail over Pacific coast states...north of cut-off cyclone retrograding westward from Baja California California. Moisture-channel imagery indicates shortwave trough moving southeastward across southern Iowa...northwestern MO...southeastern Kansas...and central/eastern OK at this time. This perturbation will maintain positive tilt as it moves southeastward to Tennessee Valley...northern la and NE Texas by 00z...crossing central/southern Appalachians and much of Florida Panhandle by 12z. Associated surface low over southeastern Iowa/northestern MO is forecast to move southeastward to near Indiana/Kentucky border by 00z...with warm front eastward over WV and cold front southwestward across Ozarks. By end of period...low should move along warm front to WV with cold front southwestward across Tennessee Valley region. Separate surface cyclogenesis may begin around 12z just offshore northestern NC. ..mid south...Tennessee Valley region... widely scattered and episodic thunderstorms are possible mainly this afternoon and early evening. In low levels...very incompletely modified return-flow trajectories are expected over this region ahead of surface cyclone...with Gulf segments being very short behind recent cold frontal passage. Low-level moisture...though weak...should be sufficient to support sporadic thunderstorms and perhaps a band or cluster of them in this area...given 1. Modest surface heating with temperatures reaching 50s f... 2. Strength of large-scale ascent and accompanying adiabatic cooling aloft...as per overlay of 00z/12z sgf radiosonde observations upstream...and 3. Lack of substantial cinh for lifted parcels. Forecast soundings suggest just enough related steepening of low-middle-level lapse rates to support marginal MLCAPE at or below 300 j/kg...occasionally extending into thermal layers suitable for lightning production. A few cells may produce small hail or strong gusts but severe potential currently appears minuscule at most. Thunderstorm coverage should diminish quickly after dark...as surface-based buoyancy vanishes and instability aloft gets shallower. .Edwards/picca.. 01/25/2015
Posted on: Sun, 25 Jan 2015 14:11:13 +0000