SPC 1730Z Day 2 Outlook
DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1228 PM CDT SUN APR 29 2012 VALID 301200Z - 011200Z ...THERE IS A SLGT RISK OF SVR TSTMS OVER A PORTION OF THE SRN AND CENTRAL PLAINS... ...THERE IS A SLGT RISK OF SVR TSTMS OVER A PORTION OF THE MID MS AND OH VALLEYS... ...SYNOPSIS... THE BLOCKING PATTERN WILL CONTINUE TO BREAK DOWN AND TRANSITION TO QUASI-ZONAL WITH SEVERAL LOW AMPLITUDE IMPULSES MOVING THROUGH THIS REGIME. TWO...SOMEWHAT MORE PROMINENT...IMPULSES SHOULD PROVIDE THE GREATEST FORCING FOR TSTM DEVELOPMENT ON MON. THE LEAD SHORTWAVE TROUGH WILL DEAMPLIFY AS IT TRACKS THROUGH THE GREAT LAKES TO THE NERN STATES RESULTING IN WEAK HEIGHT FALLS ACROSS THE OH VALLEY. AN UPSTREAM IMPULSE...NOW MOVING ESEWD THROUGH CENTRAL CA/NV...IS EXPECTED TO PROGRESS FROM THE FOUR CORNERS REGION INTO THE CENTRAL HIGH PLAINS REGION BY LATE MON AFTERNOON. AT 12Z MON...A SURFACE FRONT IS EXPECTED TO EXTEND WNWWD FROM NC THROUGH ERN KY TO AN AREA OF LOW PRESSURE...ATTENDANT TO THE PROGRESSIVE UPPER MS VALLEY TROUGH...LOCATED OVER NRN IL. THIS LOW WILL TRACK INTO THE LOWER GREAT LAKES...WHILE THE OH VALLEY PORTION OF THE AFOREMENTIONED FRONT ADVANCES NEWD AS A WARM FRONT...REACHING CENTRAL NY/PA TO WRN VA BY 12Z TUE. MEANWHILE...A FRONTAL ZONE TRAILING SWWD FROM NRN IL THROUGH CENTRAL MO WILL ADVANCE ESEWD INTO THE OH VALLEY. THE TRAILING PORTION OF THIS BOUNDARY EXTENDING INTO TO NRN OK AND THE NRN TX PANHANDLE SHOULD WEAKEN...BECOMING ILL-DEFINED. A DRY LINE IS EXPECTED TO SHARPEN FROM WRN KS INTO WRN TX. CONVECTION WITH EMBEDDED TSTMS SHOULD BE ONGOING AT THE START OF D2 FROM IN VICINITY AND E/NE OF THE SURFACE LOW NEAR CHICAGO...AND SWWD ALONG THE TRAILING FRONT INTO OK AND THE TX/OK PANHANDLES. MODELS CONTINUE TO SUGGEST TWO AREAS WITH GREATER RISKS FOR SEVERE WEATHER ON MON...1/ IN THE OH VALLEY...AND 2/ ACROSS PARTS OF THE SRN AND CENTRAL PLAINS. ...SRN AND CENTRAL PLAINS... THE SCENARIO FORECAST IN THE INITIAL D2 CONTINUES TO BE SUPPORTED BY THE LATEST MODELS FOR THIS REGION. LOW LEVEL WINDS INITIALLY WILL BE VEERED OVER THE CNTRL/SRN PLAINS AS A RESULT OF A LLJ SHIFTING NEWD TOWARD THE OH VALLEY WITH THE LEAD SHORTWAVE TROUGH. THUS EARLY CONVECTION MAY GRADUALLY DIMINISH FROM THE WEST ALLOWING FOR AT LEAST PARTIAL CLEARING IN WRN PORTIONS OF WARM SECTOR FROM WRN KS SWD THROUGH WRN OK AND WRN TX. IF THIS OCCURS...MODERATE INSTABILITY WILL DEVELOP WHERE THE EML PLUME WILL ADVECT EWD ABOVE AXIS OF LOW 60S DEWPOINTS SUPPORTING MLCAPE OF 1500-2000 J/KG. POTENTIAL WILL EXIST FOR STORMS TO REDEVELOP ESPECIALLY WHERE DRYLINE INTERSECTS RESIDUAL OUTFLOW BOUNDARIES OR WRN EXTENT OF CONVECTIVELY REINFORCED FRONT AS WELL AS SOME DISTANCE DOWN THE DRYLINE DURING THE AFTERNOON. FORCING FOR ASCENT ATTENDANT TO THE CA/NV IMPULSE WILL AID IN THE AFTERNOON/EVENING TSTM DEVELOPMENT. ACTIVITY WILL SUBSEQUENTLY SPREAD EWD THROUGH KS INTO PORTIONS OF OK. VERTICAL SHEAR OF 40-50 KT ACROSS THE SLIGHT RISK AREA WILL SUPPORT SUPERCELLS WITH ISOLATED LARGE HAIL AND DAMAGING WIND THE MAIN THREATS...BUT A COUPLE OF TORNADOES CANNOT BE RULED OUT. GIVEN THE EXPECTED INSTABILITY/SHEAR PARAMETER SPACE AND STEEPENING LAPSE RATES...THE POTENTIAL EXISTS FOR SOME OF THE HAIL TO BE VERY LARGE. A STRENGTHENING SLY LLJ MON EVENING/NIGHT AND SUBSEQUENT INCREASE IN WAA/ISENTROPIC ASCENT SHOULD SUPPORT TSTMS PERSISTING AFTER DARK...WITH A CONTINUED THREAT FOR SEVERE STORMS. GIVEN EXISTING UNCERTAINTY WITH REGARD TO THE EVOLUTION OF THE EARLY CONVECTION... THIS OUTLOOK WILL MAINTAIN A 15% COVERAGE AREA. ...MID MS VALLEY THROUGH OH VALLEY... NEW TSTM DEVELOPMENT IS EXPECTED ALONG THE SRN EXTENT OF THE ONGOING ACTIVITY AS WEAK HEIGHT FALLS SPREAD ACROSS THIS REGION. THE WARM SECTOR WILL BECOME MODERATELY UNSTABLE...AND THE STORMS WILL REMAIN EMBEDDED WITHIN SUFFICIENT UNIDIRECTIONAL SHEAR FOR ORGANIZATION AND A POTENTIAL SEVERE THREAT. SOME OF THE STORMS MAY BECOME CAPABLE OF PRODUCING ISOLATED DAMAGING WIND AND HAIL THROUGH EARLY EVENING... MAINTAINING THE SLIGHT RISK ACROSS THIS REGION. ..PETERS.. 04/29/2012
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day2otlk_1730.html
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