SPC 1630Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1120 AM CDT MON JUL 29 2013 VALID 291630Z - 301200Z ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CNTRL AND SRN PLAINS... ...SYNOPSIS... THE SYNOPTIC-SCALE PATTERN WILL BECOME INCREASINGLY ZONAL AS AN UPPER-LEVEL LOW OVER THE GREAT LAKES AND SWRN ONTARIO WEAKENS AND LIFTS NEWD ALONG THE ST. LAWRENCE VALLEY. A NUMBER OF WEAK MIDLEVEL PERTURBATIONS ARE EMBEDDED WITHIN THIS AIRFLOW REGIME...A COUPLE OF WHICH WILL TRACK FROM THE NRN AND CNTRL HIGH PLAINS INTO THE UPPER AND MID MS VALLEYS. IN THE LOW LEVELS...A LEE TROUGH WILL BE MAINTAINED ALONG THE HIGH PLAINS WITH A SEWD-MOVING COLD FRONT GRADUALLY OVERTAKING THIS FEATURE ACROSS THE NRN HIGH PLAINS. ELSEWHERE...A WARM FRONT WILL SLOWLY LIFT NWD THROUGH THE CNTRL PLAINS AND OZARKS. THIS BOUNDARY WILL ARC SEWD AND REMAIN STATIONARY OVER THE GULF COAST STATES BEFORE CURVING NNEWD ALONG THE ATLANTIC COASTAL STATES WHERE IT WILL EASE EWD AS A COLD FRONT. ...PORTIONS OF THE CNTRL AND SRN PLAINS THIS AFTERNOON AND EVENING... A CLUSTERS OF ELEVATED TSTMS ARE ONGOING THIS MORNING OVER CNTRL KS IN RESPONSE TO WAA/ISENTROPIC ASCENT TO THE NORTH OF THE SURFACE FRONT...AND PERHAPS THE PASSAGE OF A WEAK MIDLEVEL DISTURBANCE. THESE FORCING MECHANISMS WILL LIKELY CONTRIBUTE TO AN INCREASE IN TSTM ACTIVITY TODAY AS DAYTIME HEATING COMBINES WITH A RELATIVELY MOIST AIR MASS TO PROMOTE MODERATE INSTABILITY WITH MLCAPE VALUES APPROACHING 1000-2000 J/KG. GIVEN THE ABSENCE OF ANY APPRECIABLE CAPPING/EML...STORMS COULD BECOME NUMEROUS WITH INDIVIDUAL COLD POOLS AGGREGATING AND PROMOTING UPSCALE GROWTH INTO MULTIPLE SLOW-MOVING CLUSTERS. A CONDITIONAL RISK FOR SUPERCELLS WILL EXIST DURING THE EARLY STAGE OF THIS CONVECTIVE EVOLUTION OWING TO THE PRESENCE OF A VERTICAL WIND PROFILE CHARACTERIZED BY PRONOUNCED VEERING WITH HEIGHT AND 30-40 KT OF DEEP-LAYER SHEAR. UNDER THIS SCENARIO...THE POTENTIAL WILL EXIST FOR A COUPLE OF TORNADOES IN ADDITION TO LOCALLY DAMAGING WINDS AND SOME HAIL...PRIOR TO THE TRANSITION TO A MAINLY HEAVY RAINFALL THREAT. ...NEW ENGLAND THIS AFTERNOON INTO EVENING... THE NEWD PROGRESSION OF THE UPPER-LEVEL TROUGH WILL ENHANCE VERTICAL SHEAR AND FORCING OF ASCENT ALONG THE COLD FRONT WITH SCATTERED STORMS DEVELOPING THIS AFTERNOON. WEAK MIDLEVEL LAPSE RATES AND LINGERING CLOUDS ARE EXPECTED TO SLOW AIR MASS DESTABILIZATION AND LIMIT THE POTENTIAL FOR AN ORGANIZED SEVERE WEATHER EPISODE. NONETHELESS...SUFFICIENT VERTICAL SHEAR AND INSTABILITY WILL EXIST FOR ISOLATED OCCURRENCES OF DAMAGING WINDS AND HAIL INTO THIS EVENING. ...NRN PLAINS THIS AFTERNOON AND EVENING... MORNING WATER VAPOR IMAGERY SHOWS A MIDLEVEL VORTICITY MAXIMUM OVER ERN MT WHICH WILL TRANSLATE EWD...ENHANCING DEEP-LAYER ASCENT ALONG THE ASSOCIATED COLD FRONT WHICH WILL OVERTAKE THE SURFACE LEE TROUGH. DIURNALLY ENHANCED SURFACE-BASED STORM DEVELOPMENT MAY ARISE FROM ONGOING STORMS ACROSS WRN ND AND/OR ALONG THE EWD-MOVING COLD FRONT. SOME STEEPENING OF MIDLEVEL LAPSE RATES FROM THE WEST WILL COMBINE WITH DAYTIME HEATING AND BOUNDARY LAYER DEWPOINTS IN THE 50S TO YIELD POCKETS OF MODERATE INSTABILITY BY AFTERNOON WHERE MLCAPE WILL APPROACH 1000-1500 J/KG. WHEN COUPLED WITH A VERTICALLY VEERING WIND PROFILE WITH 30-35 KT OF DEEP-LAYER SHEAR...THE SETUP WILL BE FAVORABLE FOR A FEW SEVERE STORMS CAPABLE OF DAMAGING WINDS AND HAIL THROUGH THIS EVENING. ...SRN ATLANTIC COAST THIS AFTERNOON... WIDELY SCATTERED STORMS ARE EXPECTED TO DEVELOP THIS AFTERNOON ALONG THE SYNOPTIC COLD FRONT AND DEVELOPING SEA BREEZE BOUNDARY AMIDST A MOIST AND MODERATELY UNSTABLE AIR MASS. WHILE WEAK VERTICAL SHEAR AND POOR MIDLEVEL LAPSE RATES WILL LIMIT UPDRAFT INTENSITY...LOCALLY DAMAGING WET MICROBURSTS WILL BE POSSIBLE. ..MEAD/SMITH.. 07/29/2013
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_1630.html
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