SPC 1630Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1126 AM CDT MON APR 30 2012 VALID 301630Z - 011200Z ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE OH VALLEY... ...THERE IS A SLGT RISK OF SVR TSTMS CNTRL AND SRN PLAINS... ...SYNOPSIS... A BROADLY CYCLONIC...AND PROGRESSIVE LARGE-SCALE FLOW REGIME WILL BE MAINTAINED OVER THE CONUS THROUGH THE D1 PERIOD. SEVERAL EMBEDDED VORTICITY MAXIMA ARE EVIDENT IN WATER VAPOR IMAGERY...ONE OF WHICH WILL MOVE FROM ERN KS/OK INTO THE OH VALLEY TODAY...WHILE AN UPSTREAM IMPULSE TRANSLATES FROM THE FOUR CORNERS REGION INTO THE CNTRL/SRN HIGH PLAINS. AT THE SURFACE...LOW PRESSURE ATTENDANT TO THE FORMER PERTURBATION WILL DEVELOP FROM NERN IL EWD ACROSS THE NRN OH VALLEY TODAY...PRECEDED BY A WARM FRONT LIFTING INTO LOWER GREAT LAKES. A TRAILING COLD FRONT WILL SETTLE SEWD TOWARD THE OH RIVER WITH THE WRN EXTENSION OF THIS BOUNDARY REMAINING QUASI-STATIONARY OR LIFTING NWD AS A WARM FRONT FROM THE OZARKS INTO CNTRL HIGH PLAINS. FINALLY AN OUTFLOW BOUNDARY FROM S-CNTRL MO/NWRN AR THROUGH THE RED RIVER VALLEY INTO SRN TX PNHDL IS EXPECTED TO WEAKEN TODAY. ...OH VALLEY THIS AFTERNOON INTO TONIGHT... MASS RESPONSE TO ABOVE-MENTIONED SHORTWAVE TROUGH WILL SUSTAIN A SWLY 20-30 KT LLJ ACROSS THE REGION...ENHANCING THE NEWD FLUX OF AN INCREASINGLY MOIST AIR MASS. WHEN COUPLED WITH STRONGER DIABATIC WARMING OF BOUNDARY LAYER TO S OF DENSER CLOUD CANOPY...ENVIRONMENT IS EXPECTED TO BECOME MODERATELY UNSTABLE BY AFTERNOON WITH MLCAPE APPROACHING 1000-2000 J/KG. CONVERGENCE INVOF THE MIGRATORY SURFACE LOW AND COLD FRONT WILL BE AUGMENTED BY DEEP ASCENT AHEAD OF SHORTWAVE TROUGH...YIELDING AN INCREASE IN TSTMS THIS AFTERNOON INITIALLY FROM SRN IL INTO IND. THIS ACTIVITY WILL SPREAD EWD INTO THE UPPER OH VALLEY BY LATE AFTERNOON INTO EVENING...IN TANDEM WITH THE SURFACE LOW. THE COLLOCATION OF 45-55 KT FLOW IN THE MIDLEVELS AND THE LLJ WILL RESULT IN A UNIDIRECTIONAL WIND PROFILE WITH 40-50 KT OF DEEP-LAYER SHEAR. WHEN COUPLED WITH THE MODERATE INSTABILITY...SETUP WILL SUPPORT BOWING LINE SEGMENTS AND SUPERCELLS STORM MODES WITH AN ATTENDANT RISK FOR DAMAGING WINDS...LARGE HAIL...AND PERHAPS A BRIEF TORNADO. EXPECT THIS SEVERE WEATHER THREAT TO PERSIST INTO TONIGHT ACROSS PORTIONS OF OH/PA/WV/KY IN CONJUNCTION WITH AN EWD-MOVING MCS. ...CNTRL/SRN PLAINS THIS AFTERNOON AND TONIGHT... CURRENT VWP DATA INDICATE THAT ABOVE-MENTIONED OUTFLOW BOUNDARY IS BECOMING EXCEEDINGLY SHALLOW...CASTING UNCERTAINTY AS TO WHETHER IT WILL BE A VIABLE MECHANISM FOR STORM INITIATION LATER TODAY. A MORE LIKELY CANDIDATE APPEARS TO BE THE DRYLINE WHICH WILL STRENGTHEN ACROSS WRN TX WITHIN A BACKGROUND ENVIRONMENT CHARACTERIZED BY INCREASING LARGE-SCALE FORCING AHEAD OF AN IMPULSE MOVING OUT OF THE CNTRL/SRN ROCKIES. 12Z OBSERVED SOUNDINGS SHOWED A NOTABLY WEAKER CAP WITH NWD EXTENT...SUGGESTING INITIAL STORM DEVELOPMENT IS MORE PROBABLE OVER THE TX PNHDL AND S PLAINS...PERHAPS NWD INTO SWRN KS. THE JUXTAPOSITION OF STEEP MIDLEVEL LAPSE RATES AND A RELATIVELY MOIST BOUNDARY LAYER WILL YIELD MODERATE-STRONG INSTABILITY BY AFTERNOON WITH MLCAPE VALUES APPROACHING 1500-3000+ J/KG. WHEN COUPLED WITH 40-50 KT OF DEEP WLY SHEAR...SETUP WILL FAVOR SUPERCELLS CAPABLE OF MAINLY LARGE HAIL. LOW-LEVEL SHEAR IS FORECAST TO REMAIN MODEST ON THE LARGE-SCALE...WITH TORNADO POTENTIAL CONDITIONAL ON CORRIDORS OF HIGHER SRH ALONG RESIDUAL BOUNDARIES. UPSCALE GROWTH INTO AN EWD/SEWD-MOVING MCS IS LIKELY TONIGHT WITH A CONTINUED RISK FOR DAMAGING WINDS AND HAIL SPREADING INTO LOWER ELEVATIONS OF KS/OK/TX. ..MEAD/MOSIER.. 04/30/2012
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_1630.html
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