DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 201616
SWODY1
SPC AC 201614

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1114 AM CDT SUN MAY 20 2012

VALID 201630Z - 211200Z

...THERE IS A SLGT RISK OF SVR TSTMS OVER UPPER MI..WI..NRN/CNTRL IL
INTO NWRN IND...

...UPPER MI..WI..NRN/CNTRL IL INTO NWRN IND...
WATER VAPOR IMAGERY INDICATES A STRONG UPPER TROUGH MOVING TOWARD
THE UPPER MS VALLEY...WITH LARGE SCALE ASCENT SPREADING INTO WI AND
WRN UPPER MI ATTM. SURFACE LOW OVER WEST CENTRAL WI IS EXPECTED TO
MOVE INTO NERN WI/CENTRAL UPPER MI BY THIS EVENING BEFORE LIFTING
INTO ONTARIO TONIGHT. A COLD FRONT EXTENDING SWD FROM THE LOW WILL
MOVE EWD ACROSS MUCH OF WI AND NWRN/WEST CENTRAL IL THIS AFTERNOON
REACHING A LINE FROM SERN LOWER MI INTO THE LOWER OH VALLEY BY LATE
TONIGHT. AHEAD OF THE COLD FRONT...VISIBLE IMAGERY SHOWS LARGELY
CLEAR SKIES PROMOTING STRONG DIURNAL HEATING...WITH SURFACE
TEMPERATURES EXPECTED TO REACH THE MID/UPPER 80S THIS AFTERNOON.
SUFFICIENT MOISTURE IS IN PLACE WITH SURFACE DEW POINTS NEAR 60F AND
PW AROUND 1 INCH...AND WHEN COUPLED WITH STEEPER MID LEVEL LAPSE
RATES THE ENVIRONMENT WILL BECOME MODERATELY UNSTABLE WITH MLCAPE OF
1500-2000 J/KG THIS AFTERNOON.

AN EARLIER BAND OF ELEVATED PRE-FRONTAL STORMS OVER NORTH CENTRAL WI
INTO WRN UPPER MI HAS SHOWN SIGNS OF WEAKENING SLIGHTLY...WHILE NEW
STORMS HAVE BEEN DEVELOPING OVER THE LAST 1-2 HRS JUST AHEAD OF THE
COLD FRONT FROM NEAR EAU NWD TOWARD ASX. AS THE COLD FRONT MOVES
EWD...THIS CONVECTION IS EXPECTED TO INCREASE IN INTENSITY AS IT
MOVES INTO AN INCREASINGLY UNSTABLE ENVIRONMENT. SWLY MID LEVEL
WINDS OF 40-50 KT ARE RESULTING IN SUFFICIENT DEEP LAYER SHEAR
/40-45 KT IN THE LOWEST 6 KM/ TO ENHANCE STORM ORGANIZATION AND
INTENSITY INCLUDING POTENTIAL FOR A FEW SUPERCELLS TO FORM...WITH
SOME STORMS POSSIBLY BECOMING SEVERE AS EARLY AS 17-18Z. ACTIVITY
IS EXPECTED TO SPREAD EWD ACROSS PARTS OF WI AND UPPER MI THROUGH
THE LATE AFTERNOON AND EVENING BEFORE GRADUALLY WEAKENING TONIGHT.
DAMAGING WIND GUSTS AND LARGE HAIL WILL BE THE PRIMARY
THREATS...ALTHOUGH A TORNADO OR TWO MAY ALSO BE POSSIBLE.

STORMS ARE EXPECTED TO DEVELOP SWD ALONG/AHEAD OF THE FRONT THIS
AFTERNOON INTO PARTS OF NWRN AND WEST CENTRAL IL AS STRONG HEATING
WEAKENS THE CAP. ALTHOUGH WINDS ALOFT AND ASSOCIATED VERTICAL SHEAR
WILL GRADUALLY DIMINISH WITH SWD EXTENT...ORGANIZED MULTICELL STORMS
ARE LIKELY TO DEVELOP AND SPREAD EWD AHEAD OF THE FRONT THROUGH THE
EVENING WITH A THREAT FOR LARGE HAIL AND DAMAGING WINDS.

...NWRN TX/SWRN AND SOUTH CNTRL OK...
ACTIVE CONVECTION IS PERSISTING OVER PARTS OF CENTRAL/SRN
OK...ESTABLISHING AN EFFECTIVE BOUNDARY/DIFFERENTIAL HEATING ZONE
ACROSS THE RED RIVER VALLEY. STRONG DIABATIC HEATING OCCURRING
SOUTH OF THE BOUNDARY WILL STRENGTHEN MESOSCALE CIRCULATIONS AND
POSSIBLY INCREASE LOW LEVEL SUPPORT FOR ADDITIONAL STORM DEVELOPMENT
THIS AFTERNOON AND EVENING. HOWEVER...THERE ARE NO IDENTIFIABLE
FEATURES ALOFT IN SATELLITE IMAGERY TO ENHANCE LARGE SCALE ASCENT
AND FORECASTS OF RISING HEIGHTS OVER THE AREA SUGGEST UPPER LEVEL
SUPPORT WILL BE NEUTRAL AT BEST. THIS IS REFLECTED BY VARIABILITY
IN MODEL GUIDANCE FOR CONVECTIVE STORM REDEVELOPMENT. GIVEN THE
UNCERTAINTY PRESENT AT THIS TIME WILL OPT TO MAINTAIN MARGINAL
SEVERE PROBABILITY VALUES FOR HAIL/WIND ATTM. MESOSCALE ASPECTS OF
THE REGIONAL ENVIRONMENT WILL CONTINUE TO BE MONITORED GIVEN THE
HIGH CONDITIONAL PROBABILITY OF SEVERE STORMS SHOULD DEEP CONVECTIVE
DEVELOP.

...SOUTH OF THE SLGT RISK AREA INTO THE TN VALLEY AND MID-SOUTH...
ASCENT IN ASSOCIATION WITH THE FRONT AND A PREFRONTAL CONFLUENCE
AXIS WILL FOSTER THE DEVELOPMENT OF ISOLATED TO WIDELY SCATTERED
CONVECTION THIS AFTERNOON. HOWEVER...THIS REGION WILL BE REMOVED TO
THE SOUTH OF THE STRONGER DEEP SHEAR AND DEEP FORCING FOR
ASCENT...YIELDING COMPARATIVELY MORE WEAKLY ORGANIZED STORM
STRUCTURES. AMPLE SFC HEATING AND COOL TEMPERATURE PROFILES ALOFT
SHOULD CONTRIBUTE TO MODERATE TO PERHAPS STRONG INSTABILITY
DEVELOPING THIS AFTERNOON...WITH ISOLATED INSTANCES OF SVR WIND/HAIL
POSSIBLE WITH PULSE/MULTICELLULAR CONVECTION.

...SOUTH FL...
ISOLATED TO SCATTERED THUNDERSTORMS WILL DEVELOP THIS AFTERNOON
ALONG SEA BREEZE CONVERGENCE ZONES BENEATH MODESTLY STRONG
HIGH-LEVEL FLOW YIELDING EFFECTIVE BULK SHEAR MAGNITUDES AROUND
20-25 KT. AND...WITH THE DEVELOPMENT OF MODERATE INSTABILITY AMIDST
PW VALUES OF 1.3 TO 1.6 INCH PER GPS DATA...MULTICELL CLUSTERS WITH
ISOLATED SVR WIND/HAIL MAY ENSUE.

...FRONT RANGE OF THE ROCKIES THIS AFTERNOON...
WEAK MOIST SELY UPSLOPE LOW-LEVEL FLOW BENEATH NWLY FLOW IN THE
MID/UPPER LEVELS MAY SUPPORT A THREAT FOR WEAK SUPERCELL STRUCTURES
WITH ISOLATED TO WIDELY SCATTERED THUNDERSTORMS. HOWEVER...BUOYANCY
IS EXPECTED TO REMAIN MARGINAL OWING TO THE LIMITED QUANTITY OF
BOUNDARY-LAYER MOISTURE WITH SFC DEWPOINTS MAINLY IN THE 40-45F
RANGE. MARGINALLY SVR HAIL/WIND CANNOT BE RULED OUT WITH THIS
ACTIVITY...ESPECIALLY FOR LOCATIONS IN CLOSER PROXIMITY TO HIGHER
TERRAIN.

..WEISS/GARNER.. 05/20/2012

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