SPC 2000Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0259 PM CDT SAT MAY 05 2012 VALID 052000Z - 061200Z ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CNTRL PLAINS...NRN PLAINS...UPPER MIDWEST AND MID-MO VALLEY... ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE SRN PLAINS... ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE GULF COAST STATES AND CAROLINAS... THE ONLY CHANGE TO THE OUTLOOK IS TO EXTEND THE SLIGHT RISK AREA FURTHER TO THE EAST ACROSS SW WI AND INTO NWRN IL WHERE A LINEAR MCS IS EXPECTED TO TRACK. FURTHER TO THE WEST...THUNDERSTORMS ARE EXPECTED TO INITIATE LATE THIS AFTERNOON IN SERN SD AND NERN NEB WHERE THE ENVIRONMENT IS CONDUCIVE FOR SUPERCELLS AND TORNADOES. THE MODELS APPEAR TO BE DEVELOPING STORMS TOO FAR TO THE NORTHWEST IN ECNTRL SD WHERE THE AIRMASS IS COOLER AND LESS UNSTABLE. FOR THIS REASON...WILL LEAVE THE HATCHED AREAS WITH THE 10 PERCENT TORNADO AND 30 PERCENT HAIL PROBABILITIES AS IS FURTHER TO THE SOUTHEAST. ELSEWHERE ACROSS THE CONUS...THE SLIGHT RISK AREAS IN THE GULF COAST STATES AND IN THE SRN PLAINS ARE ALIGNED ALONG THE AXIS OF STRONGEST INSTABILITY SUGGESTING NO CHANGES ARE NEEDED THERE. ..BROYLES.. 05/05/2012 .PREV DISCUSSION... /ISSUED 1120 AM CDT SAT MAY 05 2012/ ...SYNOPSIS... UPPER LOW OVER THE NRN ROCKIES WILL PROGRESS NEWD INTO SRN SASKATCHEWAN THIS PERIOD IN TANDEM WITH A 50-60 KT MIDLEVEL JET STREAK DEVELOPING FROM THE ERN GREAT BASIN AND CNTRL ROCKIES INTO NRN PLAINS. ELSEWHERE...A MIDLEVEL IMPULSE --OF CONVECTIVE ORIGIN-- OVER THE CNTRL APPALACHIANS WILL PROGRESS SEWD ACROSS VA/NC/SC...TO THE E OF A SHORTWAVE TROUGH ADVANCING INTO THE LOWER MS VALLEY. AT THE SURFACE...CURRENT ANALYSIS SHOWS AN AREA OF LOW PRESSURE OVER WRN KS WITH AN ASSOCIATED WARM/STATIONARY FRONT EXTENDING NNEWD INTO N-CNTRL/NERN NEB BEFORE CURVING SEWD THROUGH CNTRL IA INTO CNTRL IL/SRN IND. AIDED BY CONVECTIVE OUTFLOW AND THE DEVELOPMENT OF A FRONTAL WAVE...THIS BOUNDARY IS EXPECTED TO INTENSIFY TODAY ACROSS THE MID-MO VALLEY...TO THE W OF A WEAK COLD FRONT WHICH WILL BE REINFORCED TONIGHT BY A PACIFIC FRONT MOVING OUT OF THE ROCKIES. ...NRN PLAINS/UPPER MS VALLEY INTO MID AND LOWER MO VALLEY... ELEVATED SUPERCELLS ARE ONGOING THIS MORNING OVER SERN SD/SWRN MN WITHIN THE EXIT REGION OF 20-30 KT LLJ WHERE WAA AND ISENTROPIC ASCENT ARE BEING ENHANCED. 12Z OAX SOUNDING IS LIKELY A PROXY FOR THE INFLOW AIR MASS THAT IS BEING LIFTED ABOVE COMPOSITE BOUNDARY...FEATURING A MOIST BOUNDARY LAYER AND STEEP MIDLEVEL LAPSE RATES WITH MUCAPE OF 2000-3000 J/KG. GIVEN THE GRADUAL INTENSIFICATION AND BROADENING OF THE LLJ TODAY...EXPECT ONGOING ELEVATED STORMS TO PERSIST ACROSS PORTIONS OF SRN MN WITH A CONTINUED RISK FOR LARGE HAIL. BASED ON LATEST SURFACE OBSERVATIONS...IT APPEARS ACTIVE COLD POOL ASSOCIATED WITH SD STORMS MAY DISPLACE EFFECTIVE SURFACE BOUNDARY A BIT FARTHER TO THE S INTO NRN NEB THAN MODEL GUIDANCE SUGGESTS. TO THE S OF THIS BOUNDARY...THE EROSION OF LOW CLOUDS WILL ALLOW FOR STRONG DIABATIC HEATING TO OCCUR. WHEN COUPLED WITH BOUNDARY LAYER DEWPOINTS IN THE MID 60S-LOWER 70S AND THE STEEP MIDLEVEL LAPSE RATES...EXPECT AFTERNOON MLCAPE VALUES TO APPROACH 2500-3500 J/KG. PERSISTENT LOW-LEVEL WAA...CONVERGENCE ALONG THE FRONT AND WEAK MIDLEVEL HEIGHT FALLS ARE EXPECTED TO CONTRIBUTE TO SURFACE-BASED TSTM DEVELOPMENT THIS AFTERNOON OVER THE MID-MO VALLEY WITHIN A KINEMATIC ENVIRONMENT CHARACTERIZED BY A VERTICALLY VEERING WIND PROFILE AND STEADILY STRENGTHENING LOW AND DEEP-LAYER SHEAR. AS SUCH...SETUP WILL BE QUITE CONDUCIVE TO SUPERCELL EVOLUTION WITH AN ATTENDANT RISK FOR TORNADOES...VERY LARGE HAIL AND DAMAGING WINDS. UPSCALE GROWTH OF STORMS INTO AN MCS OR TWO APPEARS LIKELY TONIGHT WITH A CONTINUED THREAT FOR DAMAGING WINDS AND HAIL. ...CAROLINAS THIS AFTERNOON/EVENING... SEWD PROGRESSION OF MIDLEVEL IMPULSE MENTIONED IN SYNOPSIS WILL COMBINE WITH LOW-LEVEL UPLIFT ALONG LEE TROUGH AND DEVELOPING SEA BREEZE BOUNDARIES TO GIVE RISE TO SCATTERED TSTMS THIS AFTERNOON. MODIFICATION OF 12Z CHS/MHX SOUNDINGS FOR SURFACE TEMPERATURES IN THE MID-UPPER 80S YIELDS SBCAPE VALUES OF 2000-2500 J/KG WITH LITTLE OR NO INHIBITION. WHEN COUPLED WITH 30-35 KT OF DEEP NWLY SHEAR...SETUP WILL SUPPORT MULTICELLS AND LINE SEGMENTS CAPABLE OF DAMAGING WINDS AND HAIL INTO THIS EVENING. ...LOWER MS VALLEY INTO GA THIS AFTERNOON/EVENING... VISIBLE SATELLITE AND SURFACE OBSERVATIONS SHOW A WELL-DEFINED OUTFLOW BOUNDARY ADVANCING SWD/SWWD THROUGH WRN TN AND NRN PARTS OF AL/GA. THIS FEATURE AND SLOW EWD MOVEMENT OF SHORTWAVE TROUGH INTO THE LOWER MS VALLEY SHOULD SUPPORT WIDELY SCATTERED TSTM DEVELOPMENT LATER TODAY. 12Z REGIONAL SOUNDINGS SHOW THE PRESENCE OF MIDLEVEL LAPSE RATES OF 7.5-8.5 C/KM ATOP A MOIST BOUNDARY LAYER WHICH WILL CONTRIBUTE TO MODERATE-STRONG AFTERNOON INSTABILITY. THOUGH VERTICAL SHEAR WILL REMAIN WEAK...THE THERMODYNAMIC ENVIRONMENT WILL PROMOTE VIGOROUS UP/DOWNDRAFTS CAPABLE OF SEVERE HAIL AND DAMAGING WINDS. ...SRN PLAINS THIS AFTERNOON/EVENING... IN THE ABSENCE OF APPRECIABLE LARGE-SCALE FORCING FOR ASCENT...STRONG DAYTIME HEATING AND A DEEPENING DRYLINE CIRCULATION MAY FOSTER ISOLATED-WIDELY SCATTERED TSTM DEVELOPMENT AGAIN THIS AFTERNOON. HERE...THE COMBINATION OF VERY STEEP LAPSE RATES...MLCAPE OF 2000-3000+ J/KG AND AROUND 30 KT OF DEEP NWLY SHEAR WILL SUPPORT SUPERCELL STORM MODES WITH A RISK FOR LARGE HAIL AND DAMAGING WIND GUSTS.
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_2000.html
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