DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 272000
SWODY1
SPC AC 271958

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0258 PM CDT TUE AUG 27 2013

VALID 272000Z - 281200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM CNTRL/WRN LOWER MI INTO
CNTRL/ERN WI...

...2000 UTC UPDATE...
MID-LEVEL MOISTURE CONTINUES TO CIRCULATE AROUND THE NERN SIDE OF AN
EXPANSIVE CNTRL-CONUS ANTICYCLONE. WITH CONVECTIVE DEBRIS STREAMING
SEWD ACROSS THE GREAT LAKES REGION...WIDESPREAD CLOUD COVERAGE IS
STUNTING SFC HEATING/BOUNDARY-LAYER DESTABILIZATION ON THE
RELATIVELY WARMER SIDE OF A SFC FRONT ACROSS NRN/ERN LOWER MI INTO
OHIO. AND...WITH ONLY WEAK LOW/MID-LEVEL MASS RESPONSES ACCOMPANYING
SUBTLE PERTURBATIONS EMBEDDED IN THE MID-LEVEL FLOW PER WATER VAPOR
IMAGERY...THE SLIGHT-RISK AREA HAS BEEN CONFINED TO CNTRL/WRN LOWER
MI INTO CNTRL/ERN WI. THESE LATTER AREAS ARE WHERE RELATIVELY
GREATER INSOLATION HAS ALLOWED TEMPERATURES TO INCREASE INTO THE
UPPER 80S TO THE MIDDLE 90S AMIDST DEWPOINTS IN THE LOWER 70S.
STRONG TO PERHAPS SVR STORMS MAY EVOLVE ACROSS PARTS OF LOWER MI
OVER THE SRN FLANK OF ONGOING CONVECTION...WHICH IS BEING DRIVEN BY
THE TRANSPORT OF DIURNALLY-DESTABILIZED INFLOW ATOP A
CONVECTIVELY-REINFORCED COOL DOME. ADDITIONAL STORMS MAY CONTINUE
DEVELOPING INTO THE WARMER AIR IN CNTRL/ERN WI INVOF THE FRONT...AND
MAY ALSO BECOME STRONG TO PERHAPS SVR. PLEASE SEE SWOMCD 1783 FOR
ADDITIONAL INFORMATION REGARDING CONVECTIVE TRENDS FROM PARTS OF
LOWER MI INTO WI. STORMS MAY SPREAD SEWD INTO PARTS OF THE OHIO
VALLEY AND MID ATLANTIC THROUGH TONIGHT...THOUGH THE SVR THREAT WILL
BE LIMITED BY THE LACK OF GREATER INSTABILITY.

NO OTHER MAJOR CHANGES HAVE BEEN MADE TO THE ONGOING FORECAST.
PLEASE SEE SWOMCD 1784 FOR ADDITIONAL DETAILS REGARDING THE ISOLATED
SVR POTENTIAL OVER PORTIONS OF THE DAKOTAS. OF NOTE...AN ISOLATED
MARGINALLY SVR WIND GUST CANNOT BE RULED OUT ACROSS PARTS OF
CNTRL/ERN NV...UT...AND NRN AZ WITHIN A MONSOONAL MOISTURE
PLUME...MODEST MID/HIGH-LEVEL FLOW...AND DEEP INVERTED-VEE
THERMODYNAMIC PROFILES.

..COHEN/GOSS.. 08/27/2013

.PREV DISCUSSION... /ISSUED 1130 AM CDT TUE AUG 27 2013/

...UPPER GREAT LAKES INTO THE UPPER OH VALLEY AND CNTRL
APPALACHIANS...

MORNING SATELLITE/RADAR DATA SHOW TWO MCV/S ASSOCIATED WITH DECAYING
CLUSTERS OF THUNDERSTORMS...WITH ONE ENTERING WRN LOWER MI...AND
ANOTHER ENTERING WRN OH. WIDESPREAD CLOUD COVER COINCIDENT WITH AN
AXIS OF HIGH PW VALUES /1.5-2 INCHES/ WILL PROBABLY HINDER OPTIMAL
HEATING AND RESULTANT DESTABILIZATION FROM LOWER MI THROUGH MOST OF
OH...BUT WIDESPREAD MLCAPE VALUES OF 1500-2000 J/KG SHOULD BECOME
COMMON BY LATE AFTERNOON...WITH HIGHER VALUES POSSIBLE WITHIN
STRONGER POCKETS OF HEATING AND S OF THE MAIN CLOUD SHIELD.
AFOREMENTIONED MCV/S COULD PROVIDE A FOCUS FOR TSTM REDEVELOPMENT
ALONG THE INSTABILITY GRADIENT...WITH WEAKLY VEERING WINDS WITH
HEIGHT AND APPROXIMATELY 30-40 KT OF MIDLEVEL FLOW SUFFICIENT FOR A
FEW ORGANIZED CLUSTERS PROPAGATING SEWD. THE PRIMARY THREATS WITH
THIS ACTIVITY WILL BE DMGG WINDS AND LARGE HAIL.

TSTM DEVELOPMENT AND ASSOCIATED SVR POTENTIAL REMAINS MORE UNCLEAR
ACROSS MN/WI IN THE WAKE OF THE EARLIER MCS. A SFC LOW AND ATTENDANT
BOUNDARY ARE FORECAST TO MIGRATE ESEWD FROM S-CNTRL MN. ALTHOUGH
FORCING FOR ASCENT WILL LIKELY BE WEAK...CONVERGENCE INVOF THE
BOUNDARY AND SFC LOW MAY RESULT IN AT LEAST ISOLATED TSTM
DEVELOPMENT LATER THIS AFTERNOON. THE ENVIRONMENT HERE WILL BE
COMPARATIVELY MORE UNSTABLE THAN AREAS TO THE SE WITH MLCAPE VALUES
OF 2000-3000 J/KG LIKELY DURING PEAK HEATING. BRIEF/TRANSIENT
SUPERCELL STRUCTURES COULD BE OBSERVED...BUT DEEP-LAYER SHEAR
PROFILES SUGGEST SMALL ORGANIZED CLUSTERS CAPABLE OF PRODUCING DMGG
WINDS AND LARGE HAIL ARE MORE PROBABLE.

...PORTIONS OF THE DAKOTAS...
A WEAK UPPER IMPULSE ENTERING SWRN ND HAS CONTRIBUTED TO MORNING
CONVECTION ACROSS PARTS OF ERN MT. TSTMS SHOULD PERSIST/RE-DEVELOP
EWD LATER THIS MORNING AND AFTERNOON INTO PARTS OF SWRN/S-CNTRL ND.
GIVEN STEEP MIDLEVEL LAPSE RATES OBSERVED IN 12Z BIS SOUNDING...AND
STRONG DAYTIME HEATING FORECAST TO OCCUR...A THREAT FOR ISOLATED
LARGE HAIL AND A FEW STRONG-SVR WIND GUSTS COULD EXIST.

ISOLATED TSTM DEVELOPMENT COULD ALSO OCCUR LATE THIS AFTERNOON AND
AFTERNOON INVOF A QUASI-STATIONARY FRONT ACROSS SRN SD ARCING NWWD
INTO WRN SD. MODEST MIDLEVEL HEIGHT RISES AND WEAK FORCING FOR
ASCENT WILL LIKELY LIMIT AREAL COVERAGE...BUT 25-30 KT OF EFFECTIVE
SHEAR AND MLCAPE VALUES OF 1000-1500 J/KG WILL BE MARGINALLY
SUFFICIENT FOR BRIEF/TRANSIENT SUPERCELL STRUCTURES. STEEP LOW-LEVEL
LAPSE RATES OWING TO INTENSE DIURNAL HEATING COULD ALSO SUPPORT
ISOLATED DMGG WIND GUSTS POTENTIAL...IN ADDITION TO LARGE HAIL.

...INTERIOR WEST...
DIURNALLY ENHANCED CONVECTIVE DEVELOPMENT IS LIKELY THIS AFTERNOON
ACROSS THE INTERIOR WEST...WITHIN A BAND OF 1-1.5 INCH PW LOCATED
ALONG THE WRN PERIPHERY OF LARGE-SCALE ANTICYCLONIC FLOW. MIDLEVEL
FLOW OF 15-25 KT COMBINED WITH STEEPENING LOW-LEVEL LAPSE RATES
COULD CONTRIBUTE TO A FEW STRONG WIND GUSTS.

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