SPC Convective Outlook for June 12, 2013

SPC AC 120616

DAY 1 CONVECTIVE OUTLOOK CORR 1
NWS STORM PREDICTION CENTER NORMAN OK
0116 AM CDT WED JUN 12 2013

VALID 121200Z - 131200Z

...THERE IS A MDT RISK OF SVR TSTMS FROM NRN IL INTO IND AND WRN
OH...

...THERE IS A SLGT RISK OF SVR TSTMS FROM IA EWD ACROSS A LARGE PART
OF THE OH VALLEY AND INTO VA/MD...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS MUCH OF MT...ERN
ID...AND NRN WY...

CORRECTED FOR WORDING

...WIDESPREAD DAMAGING WINDS...LARGE HAIL AND A FEW TORNADOES
EXPECTED ACROSS A LARGE AREA FROM IA INTO WV...

...SYNOPSIS...
A POTENT SHORTWAVE TROUGH WILL MOVE FROM THE CNTRL PLAINS EWD INTO
IA/MO/IL BY 00Z...AND WILL CONTINUE ESEWD ACROSS THE OH VALLEY AND
WILL APPROACH THE APPALACHIANS BY 12Z THU. AT THE SURFACE...LOW
PRESSURE WILL MOVE FROM ERN NEB INTO ERN IA/NRN IL BY LATE
AFTERNOON...WITH DIFFUSE WARM FRONT FROM SRN WI INTO LOWER MI DURING
THE DAY...THEN SHIFTING NWD ACROSS PA INTO THUR MORNING. A COLD
FRONT WILL TRAIL THE LOW AS IT DEEPENS OVERNIGHT...EXTENDING FROM OH
SWWD ALONG THE OH RIVER THUR MORNING.

TO THE W...A LARGE UPPER TROUGH WILL SLOWLY PIVOT EWD ACROSS THE
PACIFIC NW...WITH SWLY FLOW ALOFT ACROSS IA/WY/MT AND AN INVERTED
SURFACE TROUGH FOCUSING DAYTIME STORMS THERE.

...IA...IL AND SRN WI EARLY AFTERNOON INTO IND...OH...NRN KY AND FAR
SRN MI DURING THE EVENING...
MORNING STORMS ARE EXPECTED TO BE IN PROGRESS ACROSS SRN MN/IA AND
VICINITY...WITH SOME MARGINAL SEVERE WIND/HAIL THREAT. AS THE LOW
DEVELOPS...THESE STORMS WILL LIKELY BEGIN TO GROW UPSCALE WITH A
RAPIDLY DESTABILIZING AIR MASS TO THE E. OTHER CONVECTION MAY ALSO
FORM ALONG THE WARM FRONT E OF THE SURFACE LOW TRACK...ACROSS SRN
WI/NRN IL. INITIALLY...SOME OF THESE CELLS ARE LIKELY TO BE
SUPERCELLS...AND A STRONG TORNADO COULD OCCUR. WITH TIME...AND
PARTIALLY DUE TO WEAK UPPER LEVEL FLOW...STORMS SHOULD MERGE INTO A
LARGE CLUSTER. INCREASING WIND FIELDS WILL FAVOR A FORWARD
PROPAGATING CONVECTIVE SYSTEM...POSSIBLY A DERECHO CAPABLE OF
WIDESPREAD DAMAGING WINDS. HOWEVER...EMBEDDED AREAS OF ROTATION MAY
ALSO EXIST PERIODICALLY...INDICATING EITHER TORNADOES OR ENHANCED
SWATHS OF DAMAGING WIND POTENTIAL. LARGE HAIL IS ALSO
LIKELY...POSSIBLY WIND DRIVEN.

MODELS INDICATE THE MAIN CORRIDOR FOR WIDESPREAD DAMAGE WILL BE FROM
NRN IL INTO NRN AND CNTRL IND AND INTO OH. HOWEVER...IF THE SYSTEM
GROWS LARGER THAN EXPECTED...OTHER AREAS COULD BE UNDER A GREATER
THREAT SUCH AS NRN KY...WV...AND WRN PA.

...SRN MI INTO OH...WV...WRN PA LATE AFTERNOON...
ALTHOUGH THE MAIN SURFACE LOW WILL BE OVER IL AT THIS TIME...A BROAD
AREA OF CONVERGENCE WILL EXIST NEAR A DIFFUSE WARM FRONT FROM SRN
LOWER MI INTO OH. FORECAST SOUNDINGS SHOW EXTREME
INSTABILITY...STEEP LAPSE RATES...AND VEERING WINDS WITH HEIGHT
WHICH WILL FAVOR SUPERCELLS CAPABLE OF VERY LARGE HAIL AND
TORNADOES.

...SRN IL AND IND INTO WRN KY DURING THE EVENING...
THE SRN EXTENT OF THE CONVECTIVE SYSTEM...EITHER NEAR THE FRONT OR
ALONG SURGING OUTFLOW...IS MOST LIKELY TO BE FROM SRN IL INTO WRN KY
DURING THE LATE AFTERNOON/EVENING. HOWEVER...THERE WILL BE A
CONDITIONAL THREAT OF SEVERE WIND AND HAIL...AND PERHAPS ISOLATED
TORNADOES IN THESE AREAS...AND PERHAPS A BIT FARTHER S AS IT WILL
REMAIN QUITE UNSTABLE.

...VA INTO THE DELMARVA - AFTERNOON...
BRIEF SHORTWAVE RIDGING WILL OCCUR DURING THE DAY WELL AHEAD OF THE
OH VALLEY SYSTEM...WITH STRONG HEATING AND INSTABILITY DEVELOPING.
WEAK CONVERGENCE WITHIN THE SFC TROUGH MAY BE ENOUGH FOR ISOLATED
STORMS CAPABLE OF HAIL OR WIND DURING THE AFTERNOON. THEN
OVERNIGHT...INSTABILITY AND SHEAR PROFILES WILL CONDITIONALLY BE
FAVORABLE FOR SEVERE WEATHER...BUT THE MAIN CONVECTIVE COMPLEX MAY
REMAIN MAINLY NW OF THE AREA AS THE MAIN SURGE IS EXPECTED ACROSS OH
AND WRN PA. HOWEVER...SUBSEQUENT OUTLOOKS WILL REASSESS AS NEW DATA
INCLUDING SPECIAL SOUNDINGS BECOME AVAILABLE.

...MT...ERN ID...NRN WY...
DAYTIME HEATING...COOL PROFILES ALOFT AND WEAK SURFACE CONVERGENCE
WILL HELP INITIATE SCATTERED THUNDERSTORMS DURING THE AFTERNOON. THE
STEEP LAPSE RATES AND AMPLE DEEP LAYER SHEAR WILL FAVOR SUPERCELLS
CAPABLE OF MAINLY LARGE HAIL...ALTHOUGH A FEW DAMAGING WIND GUSTS
COULD OCCUR WITH SMALL BOWING CELLS. GIVEN BACKED SURFACE FLOW AND
FAVORABLE STORM MODE...A BRIEF TORNADO CANNOT BE RULED OUT.

..JEWELL.. 06/12/2013

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