SPC 1200Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1254 AM CDT SAT MAY 18 2013 VALID 181200Z - 191200Z ...THERE IS A MDT RISK OF SVR TSTMS FOR PARTS OF WRN OK AND WRN KS... ...THERE IS A SLGT RISK OF SVR TSTMS FOR A LARGE PORTION OF THE PLAINS STATES... ...AN ACTIVE SEVERE WEATHER DAY IS EXPECTED OVER A LARGE PORTION OF THE PLAINS. LARGE DESTRUCTIVE HAIL AND THE POSSIBILITY FOR A FEW STRONG TORNADOES ARE THE MAIN THREATS... ...SYNOPSIS... INCREASING CYCLONIC MID-UPPER FLOW WILL OVERSPREAD MUCH OF THE PLAINS THROUGH THE DAY 1 PERIOD DOWNSTREAM OF AN APPROACHING LARGER SCALE WRN U.S. TROUGH. THE PRIMARY UPPER TROUGH AXIS WILL MOVE FROM THE GREAT BASIN TO THE CNTRL ROCKIES-SRN HIGH PLAINS BY SUNDAY MORNING. AN ELONGATED LEE TROUGH WILL CONSOLIDATE INTO A LOW FORECAST INVOF THE ERN CO/WRN KS BORDER BY 00Z/19. A MOISTURE RICH RESERVOIR OVER THE SRN PLAINS WILL CONTINUE TO BE DRAWN NWWD INTO PORTIONS OF THE CNTRL HIGH PLAINS E OF A SHARPENING DRYLINE BY AFTERNOON. SEVERE STORMS ARE EXPECTED TO DEVELOP DURING THE AFTERNOON-EVENING HOURS WITH SOME OF THESE STORMS CONTINUING WELL AFTER DARK. ...PLAINS... FRIDAY EVENING WATER VAPOR IMAGERY SHOWS A LEAD SHORTWAVE TROUGH OVER SRN NM AND THIS FEATURE IS FORECAST TO MOVE INTO CNTRL KS-OK BY EARLY-MID AFTERNOON. DESPITE IMPLIED SUBSIDENCE IN ITS WAKE...THE APPROACH OF THE LARGER SCALE TROUGH AND ASSOCIATED HEIGHT FALLS /FORCING FOR ASCENT/ WILL OVERSPREAD THE HIGH PLAINS DURING THE AFTERNOON-EVENING. BENEATH THE STOUT EML...HIGH QUALITY BOUNDARY LAYER MOISTURE SAMPLED BY RAOBS OVER THE SRN PLAINS FRIDAY EVENING /15-16 G/KG 100MB MEAN MIXING RATIO/...WILL LEAD TO DEWPOINTS RANGING FROM THE LOWER 60S OVER THE DAKOTAS TO THE UPPER 60S AND LOWER 70S FARTHER S OVER OK/KS BY MID AFTERNOON. STRONG DIABATIC HEATING ALONG THE DRYLINE WILL CONSIDERABLY WEAKEN AN INITIALLY STOUT CAP BY MID-LATE AFTERNOON. VERY STEEP MID LEVEL LAPSE RATES IN EXCESS OF 8-9 DEG C/KM IN COMBINATION WITH THIS RICH MOISTURE WILL CONTRIBUTE TO MODERATE INSTABILITY OVER PARTS OF THE NRN PLAINS TO EXTREME INSTABILITY /4000-5000 J/KG MLCAPE/ OVER PARTS OF KS INTO NWRN TX. ONCE THE CAP IS ERODED IN POCKETS ALONG THE DRYLINE...EXPLOSIVE UPDRAFTS WILL RAPIDLY BECOME SEVERE AND INITIALLY FAVOR LARGE TO VERY LARGE HAIL AND DMGG WINDS. SUFFICIENT DEEP LAYER SHEAR /RANGING FROM AROUND 30 KT FROM NWRN TX TO WELL INTO THE SUPERCELL RANGE FROM KS NWD/ WILL PROMOTE DISCRETE SUPERCELLS AS THE EARLY CONVECTIVE MODE. BY THE 00Z-04Z PERIOD...STRONGER LOW LEVEL MASS RESPONSE IN THE FORM OF A STRENGTHENING LLJ E AND SE OF THE KS/CO LOW OVER PARTS OF WRN KS AND WRN OK...WILL ACT TO ENLARGE HODOGRAPHS /200-500 M2/S2 EFFECTIVE SRH/ DURING THIS TIMEFRAME. AS A RESULT...SUPERCELL TORNADO POTENTIAL APPEARS HIGHEST DURING THE EVENING WITH PERHAPS A STRONG TORNADO OR TWO OCCURRING. UPSCALE GROWTH MAY EVENTUALLY OCCUR WITH ANY PERSISTENT OR REGENERATIVE CLUSTER OF SUPERCELLS WITH A LINGERING OVERNIGHT THREAT FOR A FEW TORNADOES AND DMGG WINDS. ...SRN APPALACHIANS... A WEAKENING MID LEVEL TROUGH OVER THE SRN APPALACHIANS VICINITY WILL LIKELY PROVIDE AN IMPETUS FOR DIURNALLY-DRIVEN STORMS AS SURFACE HEATING LEADS TO THE POSSIBILITY FOR A FEW STRONG STORMS CAPABLE OF LOCALLY DMGG WIND. THIS ACTIVITY WILL LIKELY WANE IN INTENSITY BY THE EVENING AS THE BOUNDARY LAYER STABILIZES. ..SMITH/MARSH.. 05/18/2013
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_1200.html
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