SWODY1
SPC AC 120600
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0100 AM CDT TUE MAY 12 2009
VALID 121200Z - 131200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE NORTH-CENTRAL PLAINS
AND MISSOURI VALLEY...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF
WEST/SOUTHWEST TX...
...NORTHERN/CENTRAL PLAINS...
CONSIDERABLE UPPER TROUGH/ASSOCIATED COLD FRONT WILL DEVELOP
EASTWARD OVER THE NORTHERN INTERMOUNTAIN REGION TODAY...WITH
DOWNSTREAM HEIGHT FALLS AND LEE CYCLOGENESIS ACROSS THE NORTHERN
HIGH PLAINS. WITH A MOISTURE-RICH AIRMASS CONFINED TO THE SOUTHERN
PLAINS...MODEST BOUNDARY LAYER MOISTURE /SURFACE DEWPOINTS MAINLY
40S F TO LOWER 50S/ WILL TEND TO BE A LIMITING FACTOR...ALTHOUGH A
VERY STEEP LAPSE RATE ENVIRONMENT/STRONG SHEAR AMIDST STRENGTHENING
FLOW ALOFT /50+ KT AT 500 MB/ WILL SUPPORT A SEVERE RISK THIS
AFTERNOON/TONIGHT. STORMS SHOULD INITIALLY DEVELOP THIS AFTERNOON
ACROSS PORTIONS OF SOUTHEAST MT/ADJACENT NORTHEAST WY...AS WELL AS
THE WESTERN PORTIONS OF SD/NEB...AND SUBSEQUENTLY DEVELOP EASTWARD
THROUGH EARLY/MID EVENING. GIVEN A WELL-MIXED/STEEP LAPSE RATE
ENVIRONMENT...DAMAGING WIND GUSTS AND SEVERE HAIL WILL BE THE
PRIMARY HAZARDS.
...LOWER/MIDDLE MO VALLEY TOWARD THE MIDDLE/UPPER MS VALLEY...
STRONG NORTH-NORTHEASTWARD MOISTURE TRANSPORT REGIME WILL CONTINUE
THROUGH THE DAY ACROSS THE PLAINS AND ADJACENT MIDWEST. ON THE EDGE
OF A STRONG ELEVATED MIXED LAYER ACROSS THE PLAINS...TSTMS COULD
DEVELOP AS EARLY AS MIDDAY/EARLY AFTERNOON ACROSS PORTIONS OF THE
LOWER MO VALLEY...AIDED BY A LOW AMPLITUDE IMPULSE CROSSING THE
CENTRAL PLAINS. AMPLE VERTICAL SHEAR AND AN UNSTABLE SOURCE REGION
AIRMASS WOULD SUPPORT A SEVERE HAIL RISK ATOP A RELATIVELY STABLE
BOUNDARY LAYER. IN THE WAKE OF THESE EARLY DAY/AFTERNOON TSTMS...AN
INTENSIFYING SOUTHWESTERLY LOW LEVEL JET /50-65 KT/ WILL AGAIN
RESULT IN AN UPSWING IN TSTM COVERAGE AND HAIL POTENTIAL ACROSS THE
MIDWEST LATE THIS EVENING/OVERNIGHT...AS A RATHER/MOIST UNSTABLE
ELEVATED AIRMASS ADVECTS TOWARD THE REGION.
...WEST/SOUTHWEST TX...
WITH PERTURBED WESTERLY FLOW ALOFT AND LATE AFTERNOON/EVENING
ARRIVAL OF LARGE SCALE HEIGHT FALLS ACROSS THE SOUTHERN HIGH
PLAINS...ISOLATED TO SCATTERED TSTMS SEEM LIKELY TO DEVELOP IN
VICINITY OF DRYLINE ACROSS PORTIONS OF WEST CENTRAL/SOUTHWEST TX.
THE REGION WILL BE ON THE SOUTHERN FRINGE OF THE STRONGER
WESTERLIES...BUT INCREASING HIGH LEVEL FLOW /40 KT AROUND 8 KM/ AND
AMPLE VEERING WILL SUPPORT SUPERCELLS BY LATE THIS AFTERNOON/EARLY
EVENING. RATHER STEEP LAPSE RATES AND STRONG INSTABILITY WILL
SUPPORT LARGE HAIL AS THE PRIMARY RISK.
...CENTRAL HIGH PLAINS...
SEVERE POTENTIAL IS MUCH MORE CONDITIONAL ACROSS THE CENTRAL HIGH
PLAINS IN VICINITY OF DRYLINE...INCLUDING PORTIONS OF FAR EASTERN
CO/SOUTHWEST NEB/WESTERN KS TO THE OK/TX PANHANDLES. ANY ISOLATED
TSTMS THAT DEVELOP LATE THIS AFTERNOON/EARLY EVENING WOULD
CONDITIONALLY BE CAPABLE OF SEVERE HAIL/STRONG WIND GUSTS GIVEN
AMPLE VERTICAL SHEAR/STEEP LAPSE RATES.
...EASTERN OK/ARKLATEX TO GULF COAST STATES/FL PENINSULA...
ISOLATED HAIL/DOWNBURSTS WILL BE POSSIBLE THIS AFTERNOON/EARLY
EVENING ALONG REMNANT FRONTAL ZONE FROM EASTERN OK/ARKLATEX TO THE
GULF COAST STATES...AND IN ASSOCIATION WITH THE FL SEA BREEZE. WEAK
SHEAR/RISING HEIGHTS ALOFT THROUGHOUT THIS CORRIDOR WILL TEND TO
KEEP THE SEVERE RISK LOCALIZED IN NATURE...AND MAINLY CONFINED TO
THIS AFTERNOON/EARLY EVENING.
...SOUTHERN NEW ENGLAND...
MODEST SURFACE HEATING...COMBINED WITH COLD MID LEVEL TEMPERATURES
/-25C TO -27C AT 500 MB/ IN ASSOCIATION WITH AN OPEN MID LEVEL
WAVE...WILL RESULT IN THE DEVELOPMENT OF MODEST SBCAPE AND THE
POTENTIAL FOR ISOLATED TSTM DEVELOPMENT THIS AFTERNOON ACROSS
SOUTHERN NEW ENGLAND/PERHAPS LONG ISLAND VICINITY. WITH POTENTIAL
FOR SURFACE BASED CAPE UP TO 500 J/KG AND A STEEP LAPSE RATE
ENVIRONMENT...SOME HAIL MAY BE POSSIBLE. WEAK LOW TO MID
TROPOSPHERIC FLOW WILL LIKELY KEEP THE HAIL THREAT MARGINAL/SPORADIC
IN NATURE...AND ANY SUCH THREAT WILL QUICKLY WANE AFTER DARK.
..GUYER/JEWELL.. 05/12/2009
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