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000
ACUS02 KWNS 201730
SWODY2
SPC AC 201728

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1228 PM CDT MON MAY 20 2013

VALID 211200Z - 221200Z

...THERE IS A MDT RISK OF SVR TSTMS OVER NERN TX...EXTREME SERN
OK...CENTRAL AND SRN AR...AND NWRN LA...

...THERE IS A SLGT RISK OF SVR TSTMS FROM TX INTO THE GREAT LAKES
REGION...

...SYNOPSIS...
UPPER FLOW PATTERN IS FORECAST TO CHANGE SLOWLY THROUGH TOMORROW AS
AN UPPER LOW OVER THE NRN PLAINS DRIFTS EWD AND WEAKENS GRADUALLY
WHILE AN UPSTREAM COLD LOW DROPS SEWD ALONG THE PACIFIC NW COAST.  A
SHORT WAVE TROUGH EVIDENT NOW OVER THE FOUR-CORNERS AREA IS EXPECTED
TO TRANSLATE EWD ACROSS THE SRN PLAINS DURING THE AFTERNOON BEFORE
LIFTING NEWD AND BECOMING ABSORBED INTO THE SERN PERIPHERY OF THE
NRN PLAINS UPPER LOW.  IN THE SOUTHEAST...A WEAK UPPER LOW IS
FORECAST TO DRIFT OVER THE FL PENINSULA.

AT THE SURFACE...A LOW OVER THE UPPER MIDWEST WILL EVOLVE SLOWLY EWD
AND WEAKEN GRADUALLY...WHILE A TRAILING COLD FRONT EXTENDING SWWD
FROM THE LOW ACROSS THE MIDDLE MS VALLEY SWWD INTO OK AND TX WILL
DRIFT SEWD.  CURRENT INDICATIONS ARE THAT PRE-FRONTAL CONVECTION
DURING THE DAY 1 OVERNIGHT HOURS WILL RESULT IN OUTFLOW BOUNDARIES
LOCATED WITHIN THE WARM SECTOR AT THE START OF THE PERIOD...AND
THESE ARE EXPECTED TO PROVIDE AN ADDITIONAL FOCUS FOR SUBSEQUENT
THUNDERSTORM REDEVELOPMENT DURING THE DIURNAL HEATING CYCLE ON
TUESDAY.

...AR/SERN OK/NERN AND CENTRAL TX...
MODEL CONSENSUS /INCLUDING CONVECTION-ALLOWING MODEL ENSEMBLES/
SUGGESTS THAT CONVECTION WILL BE OVER PARTS OF AR/OK AND NRN TX
EARLY IN THE PERIOD...WITH A COMPOSITE OUTFLOW BOUNDARY EXTENDING
FROM SERN AR INTO NERN/NORTH CENTRAL TX EARLY IN THE PERIOD.  SOUTH
OF THE BOUNDARY A WARM/MOIST AIR MASS WILL BE PRESENT WITH SURFACE
DEW POINTS IN THE UPPER 60S-LOWER 70S...AND WITH ENHANCED DIABATIC
HEATING ANTICIPATED INTO THE AFTERNOON COUPLED WITH PRE-EXISTING
MODERATE MID-LEVEL LAPSE RATES...MLCAPE OF 3000-3500 J/KG IS
EXPECTED BY THE AFTERNOON.  AS THE AFOREMENTIONED SHORT WAVE TROUGH
PROGRESSES EWD ACROSS THE SRN PLAINS DURING THE AFTERNOON...STORM
INITIATION IS EXPECTED FROM SERN OK/SWRN AR INTO PARTS OF NRN TX
NEAR THE EARLIER OUTFLOW BOUNDARY.  ADDITIONAL STORMS ARE LIKELY TO
DEVELOP SWWD NEAR/AHEAD OF THE WEAKENING FRONT INTO CENTRAL
TX...WITH ALL ACTIVITY SPREADING EWD/NEWD THROUGH THE EVENING HOURS.

ALTHOUGH LOW-LEVEL WINDS WILL GENERALLY BE AOB 20-25 KT...FORECAST
SOUNDINGS INDICATE WINDS WILL INCREASE AND VEER WITH HEIGHT IN
RESPONSE TO THE PROGRESSIVE SHORT WAVE TROUGH...PROVIDING SUFFICIENT
VERTICAL SHEAR FOR ORGANIZED CONVECTIVE STRUCTURES INCLUDING A FEW
SUPERCELLS TO DEVELOP.  VERY LARGE HAIL...DAMAGING WIND GUSTS...AND
POSSIBLY A FEW TORNADOES WILL BE POSSIBLE...ESPECIALLY WHERE
BOUNDARY INTERACTIONS MAY ENHANCE LOW LEVEL SHEAR/SRH.  ACTIVITY IS
EXPECTED TO GROW UPSCALE BY EVENING WITH SEVERAL QLCS/S FORMING
WHICH MAY RESULT IN AN INCREASE IN WIND DAMAGE POTENTIAL.  ACTIVITY
IS THEN EXPECTED TO WEAKEN GRADUALLY BY 03-6Z AS THE SHORT WAVE
TROUGH LIFTS NEWD AWAY FROM THE REGION AND DIURNAL COOLING BEGINS TO
STABILIZE THE BOUNDARY LAYER.

...MID MS VALLEY NEWD INTO THE GREAT LAKES REGION...
OVERNIGHT CONVECTION ACROSS MUCH OF THIS REGION WILL TEMPORARILY
STABILIZE THE LOCAL ENVIRONMENT AT THE BEGINNING OF THE PERIOD...AND
WILL RESULT IN A COMPLEX MESOSCALE SURFACE PATTERN WITHIN THE WARM
SECTOR. AS CONVECTION CONTINUES TO WEAKEN OVER THIS AREA DURING THE
MORNING...BREAKS IN CLOUDS WILL PERMIT REGIONS OF ENHANCED DIABATIC
HEATING AND DESTABILIZATION TO OCCUR AMIDST A WARM/MOIST LOW LEVEL
ENVIRONMENT.  ZONES OF ENHANCED LOW LEVEL CONVERGENCE ALONG REMNANT
OUTFLOW BOUNDARIES WILL PROVIDE A FOCUS FOR STORM REDEVELOPMENT BY
EARLY-MID AFTERNOON.  SWLY MID LEVEL WINDS OF 35-45 KT WILL PROVIDE
SUFFICIENT DEEP LAYER SHEAR FOR ORGANIZED STRONG/SEVERE STORMS TO
DEVELOP...WITH A THREAT FOR LARGE HAIL...DAMAGING WINDS...AND
POSSIBLY A FEW TORNADOES MAINLY THROUGH THE EVENING HOURS.

THERE IS ALSO POTENTIAL FOR SEPARATE BANDS OF STRONG/SEVERE
THUNDERSTORMS TO DEVELOP ALONG/AHEAD OF THE COLD FRONT ARCING ACROSS
WI DURING THE AFTERNOON AND EVENING.

...LOWER GREAT LAKES INTO NY/WRN MA...
GUIDANCE INDICATES STRONGER STORMS WILL BE POSSIBLE ALONG/NORTH OF A
WARM FRONT LIFTING SLOWLY NWD ACROSS THIS AREA.  ALTHOUGH LOW LEVEL
MOISTURE WILL BE INCREASING...WEAKER MID LEVEL LAPSE RATES WILL TEND
TO LIMIT THE OVERALL MAGNITUDE OF INSTABILITY WITH MLCAPE OF
1000-1500 J/KG EXPECTED.  THERE WILL BE POTENTIAL FOR ISOLATED
SEVERE STORMS DURING THE AFTERNOON AND EVENING...BUT WITH THE
STRONGER MID LEVEL WINDS EXPECTED TO BE DISPLACED NWD AWAY FROM THE
WARM FRONT...POTENTIAL FOR A MORE WIDESPREAD THREAT WILL BE LIMITED.
IF LARGER INSTABILITY THAN CURRENTLY EXPECTED DEVELOPS...AN UPGRADE
TO SLIGHT RISK MAY NEED TO BE CONSIDERED.

..WEISS.. 05/20/2013