mardi 17 juin 2014

Jun 17, 2014 0600 UTC Day 1 Convective Outlook

DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0104 AM CDT TUE JUN 17 2014

   VALID 171200Z - 181200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS EXTENDS FROM ERN MT/NERN WY
   THROUGH THE NORTHERN PLAINS...UPPER MS VALLEY...GREAT LAKES INTO
   CENTRAL PA AND WRN NY...

   ...SUMMARY...
   ISOLATED TO SCATTERED STORMS PRODUCING DAMAGING WINDS...HAIL...AND
   FEW TORNADOES WILL BE POSSIBLE FROM EASTERN MONTANA...NORTHEAST
   WYOMING...AND THE WESTERN DAKOTAS INTO THE UPPER MISSISSIPPI VALLEY
   AND GREAT LAKES.  DAMAGING WINDS AND HAIL WILL BE THE PRIMARY SEVERE
   WEATHER THREATS ACROSS LOWER MICHIGAN AND NORTHERN INDIANA TO
   CENTRAL PENNSYLVANIA AND WESTERN NEW YORK.  ISOLATED STRONG TO
   SEVERE STORMS WILL BE POSSIBLE IN THE SOUTHERN HIGH PLAINS.

   ...SYNOPTIC SETUP...
   LARGE SCALE MID-UPPER LEVEL TROUGH WILL CONTINUE TO DEVELOP OVER THE
   WRN U.S. WITH A MIDLEVEL CLOSED LOW SHIFTING SLOWLY EWD THROUGH THE
   NRN INTERMOUNTAIN WEST INTO WRN MT THIS FORECAST PERIOD.  EAST OF
   THE ROCKIES...HEIGHT RISES ARE EXPECTED ACROSS PARTS OF THE MID MO
   VALLEY AND THE UPPER MIDWEST.  MEANWHILE...A MIDLEVEL IMPULSE IS
   EXPECTED TO TRACK EWD ACROSS LOWER MI THIS AFTERNOON AND INTO THE
   LOWER GREAT LAKES BY EARLY EVENING.  MODELS INCLUDING THE ECMWF
   AGREE WITH AN UPSTREAM IMPULSE EMANATING FROM THE BASE OF THE WRN
   TROUGH WILL REACH THE CENTRAL HIGH PLAINS BY 12Z TODAY.  THIS
   FEATURE IS EXPECTED TO MOVE NEWD INTO ERN NEB/WRN IA BY LATE THIS
   AFTERNOON AND THEN TURN EWD ACROSS WI AND LOWER MI THIS EVENING AND
   TONIGHT.

   AT THE SURFACE...A WARM FRONT IS EXPECTED TO MOVE NWD INTO LOWER
   MI...SRN WI AND SRN MN...WHILE THE WRN PORTION OF THIS BOUNDARY
   STRETCHES FROM SERN SD WNWWD INTO WRN SD AND ERN MT.  A LEE TROUGH
   WILL EXTEND SWD FROM ERN MT/WY...WHILE A COLD FRONT ADVANCES EWD
   THROUGH MT/WY AND NWRN CO.  A VERY MOIST ENVIRONMENT CURRENTLY
   RESIDING ACROSS ERN NEB TO IL WITH PRECIPITABLE WATER VALUES AT OR
   ABOVE 1.5 INCHES IS EXPECTED TO EXPAND NWD ACROSS MORE OF THE UPPER
   MS VALLEY AND ALSO SPREAD E/NEWD INTO LOWER MI TO THE LOWER GREAT
   LAKES AND TO PA/NY.

   ...ERN MT/NERN WY/WRN ND/WRN AND CENTRAL SD...
   ELY LOW-LEVEL WINDS ACROSS THE DAKOTAS INTO FAR ERN MT AND NERN WY
   WILL ADVECT MOISTURE WWD WITH SURFACE DEWPOINTS IN THE UPPER 50S TO
   LOWER 60S EXPECTED BY LATE AFTERNOON INTO THE WRN DAKOTAS AND ERN
   MT/NERN WY.  THIS COMBINED WITH VERY STEEP MIDLEVEL LAPSE RATES
   /8-8.5 C PER KM/ EXPECTED ACROSS THE NRN HIGH PLAINS WILL CONTRIBUTE
   TO MODERATE-STRONG INSTABILITY. THE EVOLUTION OF THE UPPER FLOW
   PATTERN TODAY WILL SUPPORT A DIFLUENT FLOW REGIME ACROSS ERN MT/WY
   INTO THE WRN DAKOTAS.  THIS COMBINED WITH THE EXIT REGION OF 50-60
   KT 500 MB JET SPREADING ACROSS WY INTO ERN MT AND 30-40 KT ELY
   LOW-LEVEL WINDS INTO THE LEE TROUGH IN MT/WY WILL RESULT IN AN
   INCREASE IN DEEP LAYER ASCENT.  THIS WILL SUPPORT STORM INITIATION
   INVOF THE SURFACE BOUNDARIES AND THE HIGHER TERRAIN INCLUDING THE
   BLACK HILLS BY THIS AFTERNOON.  EFFECTIVE BULK SHEAR OF 40-60 KT
   WILL SUPPORT SUPERCELLS WITH ALL SEVERE HAZARDS EXPECTED. STORMS
   THAT CAN REMAIN DISCRETE WILL HAVE THE GREATEST POTENTIAL TO PRODUCE
   A TORNADO...WHILE VERY LARGE HAIL WILL BE POSSIBLE WITH INITIAL
   STORMS.  BOWING LINE SEGMENTS CAN BE EXPECTED AS WELL. 

   ...NERN NEB/SERN SD/IA/SRN MN/WI/NRN IL...
   AN EXTREMELY UNSTABLE AIR MASS /MLCAPE 3500-4500 J PER KG/ IS
   EXPECTED TO DEVELOP THIS AFTERNOON ACROSS PARTS OF THE MID MO AND
   UPPER MS VALLEYS.  MIDLEVEL HEIGHT RISES AND A CAP ARE EXPECTED TO
   LIMIT SURFACE-BASED DEVELOPMENT INTO THE MID-LATE AFTERNOON. 
   HOWEVER...ASCENT ATTENDANT TO THE ERN CO IMPULSE AND LOW-LEVEL WAA
   INVOF A LEFTOVER CONVECTIVE OUTFLOW BOUNDARY EXTENDING FROM SRN IA
   TO NERN NEB AND NEAR THE WARM FRONT SHOULD SUPPORT TSTM DEVELOPMENT
   BY LATE AFTERNOON ACROSS THIS REGION.  GIVEN THE DEGREE OF
   INSTABILITY AND STRONG BULK SHEAR /45-55 KT/...VERY LARGE HAIL AND A
   TORNADO OR TWO WILL BE POSSIBLE WITH ANY OF THE INITIAL...DISCRETE
   STORMS.  WHILE THERE IS SOME MODEL UNCERTAINTY IN THE DEVELOPMENT OF
   THIS INITIAL ACTIVITY...THE EXPECTED TIMING OF THE ERN CO IMPULSE BY
   PEAK HEATING SUGGESTS A SLIGHT RISK IS WARRANTED INCLUDING THE
   POTENTIAL FOR SIGNIFICANT HAIL.  A SWLY LLJ EXTENDING INTO IA/SRN MN
   TO SRN WI AND NRN IL THIS EVENING THROUGH THE OVERNIGHT/EARLY
   WEDNESDAY SUGGESTS THE POTENTIAL FOR UPSCALE GROWTH INTO ONE OR MORE
   MCS/S WITH DAMAGING WINDS BECOMING THE PRIMARY THREAT...THOUGH HAIL
   AND A TORNADO THREAT CANNOT BE RULED OUT.

   ...SRN GREAT LAKES TO CENTRAL PA/WRN NY...
   AT 12Z...AN MCS /POTENTIALLY PRODUCING SOME STRONGER WIND GUSTS/
   SHOULD BE LOCATED FROM WRN LOWER MI INTO NRN PARTS OF IND/IL. 
   SURFACE HEATING DOWNSTREAM OF THIS SYSTEM WITHIN THE EXPECTED
   CORRIDOR OF MOISTURE ADVECTION INTO THE UPPER OH VALLEY/LOWER GREAT
   LAKES AND ERN EXTENT OF STEEP MIDLEVEL LAPSE RATES /7-7.5 C PER KM/
   WILL SUPPORT A MODERATELY UNSTABLE AIR MASS /MLCAPE 1500-2000 J PER
   KG/.  REDEVELOPMENT ALONG THE ERN PERIPHERY OF THE MORNING MCS
   AND/OR NEW TSTM FORMATION WILL BE POSSIBLE INVOF THE WARM FRONT WITH
   STRONG/DAMAGING WINDS AND HAIL BEING THE PRIMARY THREATS AS ACTIVITY
   SPREADS E/SEWD.  CURRENT THINKING SUGGESTS STORMS WILL AFFECT SERN
   LOWER MI THROUGH PARTS OF NRN OH INTO NWRN AND CENTRAL PA...AND WRN
   NY PERHAPS AS EARLY AS LATE MORNING...AND MORE LIKELY FROM AFTERNOON
   INTO THE EVENING.

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