SPC 1300Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0733 AM CDT SUN MAY 19 2013 VALID 191300Z - 201200Z ...THERE IS A MDT RISK OF SVR TSTMS OVER PORTIONS OF EASTERN KS...WESTERN MO...AND CENTRAL/EASTERN OK... ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS MUCH OF THE CENTRAL PLAINS AND UPPER MS VALLEY... ...KS/MO/OK... MULTIPLE CLUSTERS OF THUNDERSTORMS HAVE PERSISTED OVERNIGHT ACROSS THE CENTRAL PLAINS. NEVERTHELESS...CURRENT SURFACE ANALYSIS SHOWS A VERY MOIST AND UNSTABLE AIR MASS IN PLACE OVER MUCH OF TX/OK. THIS AIR MASS IS POISED TO RETURN RAPIDLY NORTHWARD INTO EASTERN KS AND WESTERN MO BY MID AFTERNOON...SETTING THE STAGE FOR ANOTHER ACTIVE SEVERE WEATHER DAY OVER THE REGION. A RELATIVELY STRONG CAPPING INVERSION IS IN PLACE OVER THE CENTRAL PLAINS THIS MORNING. THIS CAP WILL INHIBIT SURFACE-BASED STORMS THROUGH MUCH OF THE DAY. HOWEVER...STRONG HEATING/MIXING ALONG THE DRYLINE OVER CENTRAL OK ALONG WITH FORCING IN VICINITY OF THE COLD FRONT OVER EASTERN KS ARE EXPECTED TO LEAD TO SCATTERED THUNDERSTORM DEVELOPMENT BETWEEN 20-23Z. INITIAL STORMS WILL LIKELY BE DISCRETE SUPERCELLS. THE OVERALL ENVIRONMENT APPEARS QUITE FAVORABLE FOR TORNADOES...BUT A FEW SUBTLE STORM-SCALE DETAILS WILL INFLUENCE THE OUTCOME. ONE PROBLEM MAY BE THE DEGREE OF HEATING REQUIRED TO BREAK THE CAP OVER OK AND THE RESULTING LCL HEIGHTS. NEVERTHELESS...VERY HIGH CAPE VALUES /MLCAPE OVER 4000 J/KG/ MAY OFFSET THE NEGATIVE INFLUENCES SO HAVE INCREASED TORNADO PROBABILITIES OVER PORTIONS OF THE MODERATE RISK AREA. IF STORMS CAN REMAIN DISCRETE...RAPIDLY INCREASING LOW LEVEL SHEAR AFTER 00Z /0-3KM HELICITY VALUES RISING TO 300-500 M2/S2/ WILL POSE A RISK FOR STRONG TORNADOES AS FAR EAST AS SOUTHWEST MO. OTHERWISE...THE DEGREE OF INSTABILITY...SUPERCELL STRUCTURES...AND MID LEVEL LAPSE RATES OF 8.0+ C/KM WILL PROMOTE A RISK OF VERY LARGE HAIL. STORMS MAY ORGANIZE INTO A SQUALL LINE AFTER DARK AND SPREAD EASTWARD INTO WESTERN MO WITH AN ENHANCED RISK OF WIDESPREAD DAMAGING WINDS. ...UPPER MS VALLEY INTO ND... A SURFACE LOW IS FORECAST TO REMAIN OVER SD THROUGH THIS AFTERNOON. MULTIPLE AREAS OF OVERNIGHT CONVECTION HAVE COMPLICATED THE SURFACE PATTERN OVER THE REGION AND MAKE DESTABILIZATION UNCERTAIN. HOWEVER...IT APPEARS THAT PORTIONS OF IA/MN WILL BE MOST LIKELY TO SEE SOME DAYTIME HEATING AND RETURN OF RICH MOISTURE BEFORE MAIN LARGE SCALE ASCENT ARRIVES. THIS MAY RESULT IN SCATTERED STRONG/SEVERE THUNDERSTORM DEVELOPMENT. HAIL AND DAMAGING WINDS ARE THE MAIN THREATS. BACKED LOW LEVEL WINDS EAST OF THE SURFACE LOW MAY ALSO ENHANCE SHEAR/CONVERGENCE AND RESULT IN A STRONG/SEVERE THUNDERSTORM OR TWO WITH A TORNADO POSSIBLE. ...TX... A FEW OF THE OVERNIGHT MESOSCALE MODELS HAVE SHOWN A TREND OF DEVELOPING ISOLATED STORMS SOUTHWARD ALONG THE DRYLINE AS FAR SOUTH AS CENTRAL TX. CONFIDENCE IN THIS DEVELOPMENT IS RATHER LOW. HOWEVER...ANY STORMS THAT FORM ALONG THE DRYLINE WILL HAVE THE POTENTIAL FOR VERY LARGE HAIL AND DAMAGING WINDS. ...SOUTHEAST STATES... MODERATE TO STRONG INSTABILITY IS FORECAST TO DEVELOP THIS AFTERNOON ACROSS PARTS OF GA/TN/AL. WEAK BOUNDARIES FROM OVERNIGHT STORMS MAY PROVIDE FOCUS FOR ADDITIONAL DEVELOPMENT TODAY...WITH DAMAGING WINDS AND HAIL POSSIBLE FROM THE STRONGEST STORMS. ..HART/LEITMAN.. 05/19/2013
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_1300.html
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