OWER MS VALLEY... ...SUMMARY... ISOLATED SEVERE STORMS CAPABLE OF LOCALLY DAMAGING WINDS...MARGINALLY SEVERE HAIL...AND A BRIEF TORNADO ARE POSSIBLE THIS AFTERNOON INTO TONIGHT FROM THE MIDDLE TEXAS COAST INTO PARTS OF THE LOWER MISSISSIPPI VALLEY. ...SYNOPSIS... AN AMPLIFIED SPLIT-FLOW PATTERN WILL PREVAIL OVER NORTH AMERICA WITH THE PRIMARY FEATURE OF INTEREST BEING A WEAKENING POSITIVELY-TILTED TROUGH WHICH WILL TRANSLATE FROM THE CNTRL/SRN ROCKIES INTO THE CNTRL/SRN PLAINS. AT THE SURFACE...A COLD FRONT EXTENDING FROM AN AREA OF LOW PRESSURE OVER WI SWWD INTO CNTRL TX WILL ADVANCE SEWD...WITH SOME POTENTIAL FOR WEAK CYCLONE DEVELOPMENT ALONG THIS BOUNDARY AS IT MOVES THROUGH THE LOWER MS VALLEY TONIGHT. AN ASSOCIATED WARM FRONT CURRENTLY FROM SERN TX TO SRN LA WILL DEVELOP NWD IN ADVANCE OF THE COLD FRONT AND EVOLVING SURFACE LOW. ...MIDDLE TX COAST TO LOWER MS VALLEY THIS AFTERNOON INTO TONIGHT... NUMEROUS SHOWERS AND A FEW TSTMS --BOTH OF WHICH ARE ROOTED ABOVE THE BOUNDARY LAYER-- ARE ONGOING WITHIN THE WARM CONVEYOR AIR STREAM FROM ERN TX INTO THE LOWER MS VALLEY WHERE LOW-LEVEL WARM THERMAL AND MOISTURE ADVECTIONS ARE BEING ENHANCED BY A 30 KT LLJ. THESE SAME PROCESSES WILL PROMOTE A GROWING CONVECTIVE PRECIPITATION SHIELD TODAY TO THE NORTH OF THE WARM FRONT AS BACKGROUND FORCING FOR ASCENT IS FURTHER AUGMENTED BY BROAD ISENTROPIC ASCENT WITHIN THE RIGHT ENTRANCE OF AN UPPER-LEVEL JET STREAK CENTERED OVER THE MIDWEST. TO THE SOUTH OF THIS EARLY-DAY CONVECTION...THE 12Z SOUNDINGS FROM CRP AND BRO REVEALED THE PRESENCE OF A STRONG CAP ACROSS THE PRE-FRONTAL WARM SECTOR. GIVEN NEGLIGIBLE HEIGHT FALLS/DCVA AND THAT THE STRONGER ISENTROPIC ASCENT WILL REMAIN DISPLACED TO THE NORTH OF THE AREA...IT REMAINS UNCERTAIN AS TO WHETHER STORMS DEVELOPING INVOF THE COLD FRONT LATER TODAY WILL BE TRULY SURFACE-BASED OR SLIGHTLY ELEVATED ABOVE THE FRONTAL SURFACE. WIDESPREAD CLOUDS WILL LIMIT THE DEGREE OF DESTABILIZATION WITHIN THE WARM SECTOR...THOUGH THE PRESENCE OF MID TO UPPER 60S DEWPOINTS WILL CONTRIBUTE TO MLCAPE APPROACHING 1000 J/KG. WHEN COUPLED WITH A VERTICALLY VEERING WIND PROFILE WITH 40-50 KT OF EFFECTIVE BULK SHEAR...THE SETUP WILL BE SUPPORTIVE OF TRANSIENT SUPERCELL AND/OR BOWING STRUCTURES CAPABLE OF ISOLATED OCCURRENCES OF LOCALLY DAMAGING WINDS AND HAIL...AND PERHAPS A BRIEF TORNADO. THE POTENTIAL FOR A MORE ORGANIZED SEVERE WEATHER EPISODE IS EXPECTED TO BE TEMPERED BY THE ANAFRONTAL NATURE OF THE COLD FRONT...AS WELL AS A GENERALLY WEAK LOW-LEVEL LAPSE RATES. AS SUCH...A MARGINAL CATEGORICAL DELINEATION WILL BE MAINTAINED IN THIS FORECAST. ..MEAD/ROGERS.. 12/27/2014
Posted on: Sat, 27 Dec 2014 15:27:33 +0000
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