SPC 1730Z Day 2 Outlook
DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1228 PM CDT FRI APR 27 2012 VALID 281200Z - 291200Z ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE OH VALLEY INTO SERN MO... ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PART OF THE SRN PLAINS... ...SYNOPSIS... BLOCKING UPPER LEVEL FLOW WILL PERSIST THROUGH D2 FROM CANADA INTO THE NRN THIRD TO ONE HALF OF THE CONUS AS A STRONG RIDGE REMAINS CENTERED OVER CENTRAL CANADA...AND EXTENDS SSEWD INTO THE GULF COAST STATES WITH LESS AMPLITUDE. CLOSED LOWS WILL FLANK THIS RIDGE...1/ MOVING SLOWLY NWD THROUGH THE NRN PLAINS...AND 2/ A MUCH LARGER SYSTEM ENCOMPASSING ERN CANADA INTO THE NERN STATES. MEANWHILE...MODELS ARE IN AGREEMENT WITH THE WEAKENING OF THE COMPACT D1 SHORTWAVE TROUGH AS IT MOVES QUICKLY FROM THE UPPER MS VALLEY THROUGH THE LOWER GREAT LAKES AND BASE OF THE ERN CANADA CLOSED LOW. MODELS TEND TO AGREE WITH THE TIMING OF A MORE SUBTLE MIDLEVEL IMPULSE TRACKING THROUGH THE GREAT BASIN AND SRN ROCKIES D1 AND INTO THE MID MS/OH VALLEYS ON SAT. A WARM FRONT WILL LIFT NWD TO NEAR THE OH RIVER...BUT NWD PROGRESS WILL BE IMPEDED BY A SURFACE HIGH PRESSURE CENTERED OVER ONTARIO EXTENDING SWD ACROSS THE GREAT LAKES. THE EJECTING BUT DEAMPLIFYING WAVE WILL PROVIDE IMPETUS FOR AN ATTENDANT SURFACE LOW TO TRACK SEWD FROM NRN MO INTO THE LOWER OH VALLEY TO KY...WHILE A TRAILING COLD FRONT ADVANCES SEWD. BY THE END OF THE PERIOD...THE LOW SHOULD BE LOCATED E OF THE CENTRAL APPALACHIANS WITH THE COLD FRONT EXTENDING SWWD THROUGH THE TN VALLEY TO OK...WHERE IT WILL BE RETREATING NWD AS A WARM FRONT IN THE SRN PLAINS. ...KY/SRN IND/SRN IL/PART OF SERN MO... ELEVATED SHOWERS AND TSTMS SHOULD BE IN PROGRESS FROM THE UPPER MS VALLEY INTO A PORTION OF THE OH VALLEY WITHIN ZONE OF ISENTROPIC ASCENT NORTH OF THE WARM FRONT SAT MORNING. ACTIVITY WILL SHIFT ENEWD DURING THE DAY AND LIKELY REINFORCE THE WARM FRONT AND SLOW ITS NWD PROGRESS. ATMOSPHERE WILL DESTABILIZE SOUTH OF THIS FEATURE AS AXIS OF LOW 60S DEWPOINTS ADVECT NEWD BENEATH PLUME OF STEEPER MID LEVEL LAPSE RATES. DISSIPATING LOW CLOUDS IN THE WARM SECTOR BY LATE MORNING OR AFTERNOON SHOULD ALLOW THE BOUNDARY LAYER TO DESTABILIZE WITH MLCAPE TO 1500 J/KG. POTENTIAL WILL EXIST FOR A FEW STORMS TO REDEVELOP ALONG THE CONVECTIVELY REINFORCED WARM FRONT... ESPECIALLY FROM SRN IL...SRN IND INTO THE NRN HALF OF KY WHERE SHORTWAVE RIDGE WILL BE SUPPRESSED SOME BY THE SUBTLE SHORTWAVE TROUGH. THIS REGION WILL ALSO REMAIN ON NRN FRINGE OF EML WHERE THE CAP SHOULD BE SOMEWHAT WEAKER THAN FARTHER SOUTH. OTHER STORMS MAY DEVELOP ALONG THE COLD FRONT AS IT ADVANCES SEWD. WLY UNIDIRECTIONAL SHEAR FROM 40-50 KT WILL SUPPORT ORGANIZATION INCLUDING A FEW SUPERCELLS WITH DAMAGING WIND AND LARGE HAIL THE MAIN THREATS. FORECAST SOUNDINGS SUGGEST THE POTENTIAL FOR HAILSTONES UP TO...OR LOCALLY EXCEEDING...2 INCHES IN DIAMETER DUE TO STEEP MIDLEVEL LAPSE RATES /7.5-8 C PER KM/ ACCOMPANYING THE WEAKER MIDLEVEL IMPULSE. HOWEVER...UNCERTAINTY IN THE COVERAGE OF THIS GREATER THREAT PRECLUDES THE INTRODUCTION OF SIGNIFICANT PROBABILITIES AT THIS TIME. ...OK/N TX WWD THROUGH THE TX PANHANDLE... TSTM POTENTIAL IS EXPECTED TO REMAIN LIMITED DURING THE DAY ALONG STALLING FRONT FROM NRN TX INTO THE OZARKS/SRN MO DUE TO A CAPPING INVERSION AND WEAK FRONTAL CONVERGENCE. THEREAFTER...A STRENGTHENING SLY NOCTURNAL LLJ WILL CONTRIBUTE TO NWD DESTABILIZATION OVER THE SRN PLAINS FROM N TX AND OK INTO THE PANHANDLES. ELEVATED STORMS WILL LIKELY DEVELOP WITHIN THIS ZONE OF ISENTROPIC ASCENT/STRONG WAA SATURDAY NIGHT. A BAND OF 40-50 KT SWLY MIDLEVEL WINDS EXTENDING FROM NM ACROSS OK/SRN KS WILL RESULT IN EFFECTIVE BULK SHEAR BECOMING MORE FAVORABLE /40-50 KT/ TO SUPPORT ORGANIZED STORMS. ACTIVITY SHOULD DEVELOP FROM S-N WITH MODELS NOW INDICATING STRONGER MUCAPE 1000-1500 J/KG SAT NIGHT/EARLY SUN MORNING. THIS COMBINED WITH STEEP MIDLEVEL LAPSE RATES SHOULD PROMOTE STORMS PRODUCING SEVERE HAIL. THE GREATEST POTENTIAL FOR SEVERE STORMS WILL BE FROM CENTRAL/SWRN OK INTO ERN PARTS OF THE TX PANHANDLE...AND THUS...A SLIGHT RISK AREA HAS BEEN INTRODUCED FOR THIS REGION SAT NIGHT. THERE IS SOME INDICATION FOR SURFACE BASED STORMS SAT EVENING INTO THE OVERNIGHT PERIOD...BUT CONFIDENCE IS LOWER WITH THIS THREAT. IF STORMS CAN BECOME SURFACE BASED...THEN THERE WOULD BE A THREAT FOR DAMAGING WINDS AND A TORNADO THREAT COULD NOT BE RULED OUT. ..PETERS.. 04/27/2012
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day2otlk_1730.html
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