SPC 1630Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1127 AM CDT THU AUG 23 2012 VALID 231630Z - 241200Z ...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF NWRN KS AND SWRN NEB... ...SYNOPSIS... A SPLIT FLOW REGIME WILL BE MAINTAINED THROUGH THE D1 PERIOD...FEATURING A PROGRESSIVE WAVE TRAIN ACROSS SRN CANADA AND THE NRN TIER OF STATES...AND SUB-TROPICAL BRANCH DISTURBANCES FROM THE SWRN DESERTS TO SERN ATLANTIC COAST. MORE SPECIFICALLY...A SHORTWAVE TROUGH FROM THE UPPER MS VALLEY TO ERN SASKATCHEWAN/WRN MANITOBA WILL TRANSLATE EWD INTO THE UPPER GREAT LAKES AND WRN ONTARIO. THIS SYSTEM WILL PRECEDE A MORE INTENSE SHORTWAVE TROUGH AMPLIFYING OVER BRITISH COLUMBIA/ALBERTA INTO THE PACIFIC NW AND NRN INTERMOUNTAIN REGION. FARTHER S...A VORTICITY MAXIMUM OVER THE LOWER CO VALLEY WILL MOVE SLOWLY EWD THROUGH THE FOUR CORNERS REGION. IN THE LOW LEVELS...A WEAK COLD FRONT FROM NWRN MN TO A SURFACE LOW OVER ERN SD WILL CONTINUE TO UNDERGO FRONTOLYSIS AS IT PROGRESSES SLOWLY EWD INTO THE UPPER MS VALLEY. FARTHER S...A LEE TROUGH WILL PERSIST OVER THE CNTRL/SRN HIGH PLAINS...ANCHORED BY A LEE LOW ALONG THE CO/KS BORDER. ...CNTRL HIGH PLAINS THIS AFTERNOON INTO TONIGHT... 12Z REGIONAL SOUNDINGS OBSERVED THE OVERLAP OF A MOIST BOUNDARY LAYER /LOWEST 100-MB MEAN-MIXING RATIOS OF 13-14 G PER KG/ BENEATH STEEP MIDLEVEL LAPSE RATES WHICH WILL CONTRIBUTE TO MODERATE INSTABILITY /MLCAPE OF 1000-2000 J PER KG/ E OF LEE TROUGH AND S OF DENSER MID AND HIGH-CLOUDS OVER WRN/CNTRL NEB. THOUGH LARGE-SCALE FORCING WILL REMAIN RATHER WEAK THROUGH THE PEAK OF THE DIURNAL HEATING CYCLE...LATEST MESOSCALE AND CONVECTION-ALLOWING MODEL GUIDANCE ARE IN GOOD AGREEMENT IN SUGGESTING THAT THE LEE TROUGH WILL FOCUS SURFACE-BASED STORM DEVELOPMENT OVER NWRN KS BY MID AFTERNOON. MODEST /25-30 KT/ DEEP-LAYER SHEAR WILL COINCIDE WITH THE MODERATE INSTABILITY TO SUPPORT MULTICELL STORM MODES CAPABLE OF DAMAGING WINDS AND SOME HAIL. BY LATE EVENING...THE INTERACTION OF ONGOING STORMS AND THEIR ASSOCIATED COLD POOLS WITH A DEVELOPING NOCTURNAL LOW-LEVEL WIND MAXIMUM SUGGESTS THE POTENTIAL FOR UPSCALE GROWTH INTO AN MCS WITH A RISK OF ISOLATED DAMAGING WINDS PERSISTING INTO TONIGHT. ..UPPER MS VALLEY THIS AFTERNOON AND EVENING... STRONGER FORCING FOR ASCENT ASSOCIATED WITH SRN SEGMENT OF SHORTWAVE TROUGH APPEARS TO BE PROGRESSING WELL TO THE E OF SURFACE FRONT THIS MORNING...CASTING SOME UNCERTAINTY ON AREAL COVERAGE OF TSTMS ALONG/AHEAD OF THE BOUNDARY LATER TODAY. IT DOES APPEAR THAT DAYTIME HEATING WILL AUGMENT MODEST BOUNDARY LAYER MOISTURE AND MIDLEVEL LAPSE RATES OF 7.0-7.5 C/KM TO FOSTER AFTERNOON MLCAPE VALUES OF 1000-2000 J/KG. BASED ON LATEST MODEL GUIDANCE...IT APPEARS THAT ONGOING STORMS ESE OF VVV MAY INCREASE IN COVERAGE AND INTENSITY THIS AFTERNOON AS AMBIENT AIR MASS DESTABILIZES...AND AREA IS GLANCED BY SASKATCHEWAN/MANITOBA PORTION OF SHORTWAVE TROUGH. PROFILER AND VAD DATA FROM WOODLAKE MN AND SIOUX FALLS SD...RESPECTIVELY HAVE SHOWN A GENERAL WEAKENING TREND OF THE LOW TO MID-TROPOSPHERIC WIND FIELD OWING TO THE EWD PASSAGE OF LEAD MIDLEVEL IMPULSE AND GRADUAL CESSATION OF NOCTURNAL LOW-LEVEL WIND MAXIMUM. AS SUCH...VERTICAL SHEAR IS EXPECTED TO REMAIN MARGINALLY SUPPORTIVE OF ORGANIZED STORM MODES WITH A RISK FOR LOCALLY DAMAGING WINDS AND PERHAPS SOME HAIL INTO THIS EVENING. ..MEAD/SMITH.. 08/23/2012
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_1630.html
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