SPC 2000Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0252 PM CDT TUE MAY 01 2012 VALID 012000Z - 021200Z ...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN AND EVE ACROSS PARTS OF THE N CNTRL PLAINS INTO UPPER MISSISSIPPI VALLEY... ...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN AND EVE ACROSS PARTS OF THE OH VALLEY... ...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN AND EVE ACROSS PARTS OF THE MID ATLANTIC COAST STATES... ...20Z OUTLOOK UPDATE... ONLY RELATIVELY MINOR CHANGES HAVE BEEN MADE TO THE 1630Z OUTLOOK...IN AN ATTEMPT TO BETTER ACCOUNT FOR ONGOING TRENDS IN CONVECTIVE DEVELOPMENT/DESTABILIZATION. REFER TO LATEST SPC SEVERE WEATHER WATCHES AND MESOSCALE DISCUSSIONS FOR THE LATEST DETAILS ON ONGOING OR MORE IMMINENT CONVECTIVE THREATS. ...N CNTRL PLAINS INTO THE UPPER MISSISSIPPI VALLEY... QUITE A BIT OF UNCERTAINTY LINGERS CONCERNING DETAILS OF STORM INITIATION LATE THIS AFTERNOON AND EVENING. MODERATE TO STRONG DESTABILIZATION APPEARS TO BE OCCURRING ALONG AN AXIS FROM NORTH CENTRAL NEBRASKA INTO SOUTHWEST MINNESOTA...NEAR COINCIDING AXES OF STRONGER SURFACE HEATING AND LOW-LEVEL MOISTURE...TO THE SOUTH AND SOUTHWEST OF A SURFACE LOW MIGRATING ACROSS NORTHEASTERN SOUTH DAKOTA. LARGE CLOCKWISE CURVED LOW-LEVEL HODOGRAPHS APPEAR LIKELY TO REMAIN CONFINED TO THE COOL/STABLE SIDE OF A WARM FRONTAL SHIFTING EASTWARD ACROSS PARTS OF EASTERN MINNESOTA/WESTERN WISCONSIN LATE THIS AFTERNOON AND EVENING. HOWEVER...DEEP LAYER SHEAR BENEATH 30-40 KT SOUTHWESTERLY 500 MB FLOW WILL STILL BE SUFFICIENT FOR SUPERCELLS AND DEVELOPMENT OF ORGANIZED STORM CLUSTERS. AND GUIDANCE CONTINUES TO INDICATE A GOOD LIKELIHOOD FOR STORM CONSOLIDATION AND EVOLUTION OF A SUBSTANTIAL MESOSCALE CONVECTIVE SYSTEM NEAR/EAST OF THE MID MISSOURI VALLEY AREA THIS EVENING...IN STRENGTHENING LOWER/MID TROPOSPHERIC WARM ADVECTION ...AS A SHORT WAVE IMPULSE LIFTS NORTHEAST OF THE NORTHERN ROCKIES. ..KERR.. 05/01/2012 .PREV DISCUSSION... /ISSUED 1130 AM CDT TUE MAY 01 2012/ ...SYNOPSIS... LARGE-SCALE PATTERN WILL UNDERGO SLIGHT AMPLIFICATION THIS PERIOD AS A MIDLEVEL JET STREAK AND ASSOCIATED SHORTWAVE TROUGH OVER THE NERN PACIFIC MOVE INLAND ACROSS THE PACIFIC NW INTO NRN ROCKIES. THIS SYSTEM WILL BE PRECEDED BY A SHORTWAVE TROUGH WHICH WILL TRANSLATE FROM THE NRN ROCKIES/NRN HIGH PLAINS INTO THE UPPER MS VALLEY/UPPER GREAT LAKES. FARTHER E...A VORTICITY MAXIMUM --OF CONVECTIVE ORIGIN-- OVER THE OZARKS WILL DEAMPLIFY WHILE PROGRESSING ACROSS THE OH VALLEY. AT THE SURFACE...DUAL LOW PRESSURE CENTERS OVER CNTRL SD AND ERN ND WILL DEVELOP EWD INTO THE UPPER MS VALLEY...IN TANDEM WITH A COLD FRONT PROGRESSING ACROSS THE DAKOTAS. A PRE-FRONTAL TROUGH OR DRYLINE WILL SHARPEN TODAY FROM THIS AREA OF LOW PRESSURE SWWD THROUGH CNTRL NEB INTO WRN PARTS OF KS/OK/TX...WITH A WARM FRONT BECOMING BETTER-DEFINED OVER THE UPPER MS VALLEY/UPPER GREAT LAKES. THE ERN EXTENSION OF THE WARM FRONT WILL LIFT SLOWLY NWD THROUGH THE OH VALLEY AND MID ATLANTIC STATES. ...UPPER MS VALLEY INTO MID MO VALLEY... CURRENT MEDICINE BOW WY PROFILER IS SAMPLING THE EXIT REGION OF A 50-60 KT MIDLEVEL JET STREAK WHICH WILL DEVELOP NEWD THROUGH THE RED RIVER VALLEY TODAY IN CONCERT WITH A LEAD VORTICITY MAXIMUM. FORCING ASSOCIATED WITH THESE FEATURES AND LOW-LEVEL CONVERGENCE INVOF MIGRATORY SURFACE LOWS ARE EXPECTED TO FOSTER SCATTERED TSTMS BY MID-LATE AFTERNOON FROM N-CNTRL MN SWWD ALONG COLD FRONT INTO SERN SD/NERN NEB. VISIBLE SATELLITE IMAGERY SHOWS WIDESPREAD CLOUDS ACROSS MUCH OF MN WITH THE POTENTIAL FOR STRONGER HEATING AND RESULTANT DESTABILIZATION OVER ERN SD INTO THE MID MO VALLEY. EXPECT THE CLOUDS AND MARGINAL MOISTURE CONTENT TO LIMIT MLCAPE TO 500-1000 J/KG ACROSS NRN MN...WHILE STRONGER HEATING AND A MORE MOIST BOUNDARY LAYER YIELDS AFTERNOON MLCAPE TO 1500-2500 J/KG OVER THE MID MO VALLEY. WHEN COMBINED WITH STRENGTHENING LOW AND DEEP-LAYER SHEAR...ENVIRONMENT WILL BECOME INCREASINGLY FAVORABLE FOR SUPERCELLS CAPABLE OF LARGE HAIL...DAMAGING WINDS AND A FEW TORNADOES. STORMS WILL LIKELY GROW UPSCALE INTO AN MCS OR TWO TONIGHT WITH A CONTINUED SEVERE WEATHER RISK ACROSS PARTS OF MN/WI/IA/NEB. ...MID MS/LOWER MO VALLEY THIS AFTERNOON INTO TONIGHT... LOW-LEVEL WAA ON BACKSIDE OF OH VALLEY MCV WILL INCREASE THIS AFTERNOON INTO TONIGHT IN RESPONSE TO THE DEVELOPMENT OF A 40-50 KT LLJ FROM KS/OK INTO THE REGION. THIS WILL LIKELY GIVE RISE TO SCATTERED TSTMS ALONG/N OF WARM/STATIONARY FRONT WITHIN A MODERATELY UNSTABLE ENVIRONMENT. LARGE HAIL WILL LIKELY BE THE PRIMARY THREAT WITH THESE STORMS. ...OH VALLEY THIS AFTERNOON INTO TONIGHT... MESOSCALE AND CONVECTION-ALLOWING MODEL GUIDANCE INDICATES THAT FORCING ASSOCIATED WITH MCV WILL COMBINE WITH LOW-LEVEL CONVERGENCE ALONG WARM FRONT LIFTING NWD TO FOSTER SCATTERED TSTMS ACROSS THE REGION THIS AFTERNOON. THE COMBINATION OF DAYTIME HEATING AND A MOISTENING BOUNDARY LAYER WILL YIELD A MODERATELY UNSTABLE AIR MASS LATER TODAY WHERE MLCAPE VALUES WILL APPROACH 1000-2000 J/KG. THIS INSTABILITY WILL COINCIDE WITH A BELT OF 50 KT SWLY FLOW IN THE 2-6 KM AGL LAYER /PER STL VWP/ ATTENDING MCV...RESULTING IN AN ENVIRONMENT SUPPORTIVE OF SUPERCELLS AND BOWING STRUCTURES CAPABLE OF DAMAGING WINDS AND LARGE HAIL. A TORNADO OR TWO IS POSSIBLE...NAMELY WITH ANY STORMS THAT CAN FAVORABLY INTERACT WITH THE WARM FRONT WHERE THE LOW-LEVEL SHEAR/VORTICITY IS MAXIMIZED. ...VA/NC THIS AFTERNOON/EVENING... SMALL TSTM CLUSTER OVER ERN KY APPEARS TO BE ASSOCIATED WITH AN MCV WHICH WILL TRACK ACROSS THE CNTRL APPALACHIANS AND INTO THE PIEDMONT LATER TODAY. 12Z RNK SOUNDING SHOWED THE PRESENCE OF A MOIST LOW-LEVEL AIR MASS AND WEAK CAP WITH 40-45 KT WLY FLOW OBSERVED ABOVE THE BOUNDARY LAYER. STRONG DAYTIME HEATING IS EXPECTED TO PROMOTE A STEEPENING OF LOW-LEVEL LAPSE RATES WITH MLCAPE INCREASING TO 1000-1500 J/KG. THOUGH LOW-LEVEL CONVERGENCE WILL REMAIN WEAK...CONVECTION-ALLOWING MODELS DO INDICATE AN INCREASE IN TSTMS E OF THE BLUE RIDGE THIS AFTERNOON...LIKELY IN CONJUNCTION WITH THE ABOVE-MENTIONED MCV. GIVEN THE MODERATELY STRONG UNIDIRECTIONAL WIND FIELD AND DEGREE OF INSTABILITY...SETUP WILL FAVOR THE DEVELOPMENT OF LINE SEGMENTS/BOWS CAPABLE OF DAMAGING WINDS AND PERHAPS SOME HAIL. FOR ADDITIONAL NEAR-TERM GUIDANCE...SEE MCD 643. ...SERN TX TODAY... A WELL-DEFINED MCV SE OF AUS WILL CONTINUE EWD TODAY...LIKELY SERVING AS THE FOCUS FOR DIURNALLY ENHANCED TSTM DEVELOPMENT. MODIFICATION OF 12Z CRP SOUNDING FOR FORECAST AFTERNOON SURFACE CONDITIONS SUGGESTS AIR MASS WILL BECOME MODERATELY UNSTABLE WITH MLCAPE OF 1500-2000 J/KG. MOREOVER...CURRENT CRP VWP SHOWS THE PRESENCE OF MODESTLY STRONG LOW-LEVEL SHEAR WHICH MAY PROMOTE A FEW ROTATING STORMS WITH AN ATTENDANT RISK FOR HAIL...LOCALLY DAMAGING WINDS AND PERHAPS A TORNADO.
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_2000.html
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