SWODY1
SPC AC 131605
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1105 AM CDT SUN MAY 13 2007
VALID 131630Z - 141200Z
..THERE IS A SLGT RISK OF SVR TSTMS OVER THE NRN PLAINS...
..THERE IS A SLGT RISK OF SVR TSTMS FROM NRN MN INTO THE NRN GREAT
LAKES...
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS A LARGE PART OF THE FL
PENINSULA...
..NRN PLAINS...
MAIN VORT LOBE AND ASSOCIATED SHORTWAVE TROUGH IS NOW MOVING ACROSS
ERN WA/ORE AND WILL OVERSPREAD NWRN MT/ID THIS AFTERNOON. PACIFIC
COLD FRONT WILL ACCOMPANY THIS SYSTEM AND WILL SPREAD EWD ACROSS MT
AND NRN/WRN WY THROUGH THE DAY. SURFACE LOW IS EXPECTED TO DEEPEN
OVER WRN SD ALONG E-W ORIENTED FRONT NOW EXTENDING ACROSS NRN
WY...WHILE WARM FRONT REMAINS ESTABLISHED AND POSSIBLY LIFTS A
LITTLE NWD INTO SERN ND AND NRN MN. STRONG HEATING/MIXING WILL DRY
MUCH OF THE WARM SECTOR WITH CAPPING LIKELY INHIBITING DEVELOPMENT
NEAR THE WARM FRONT OVER THE DAKOTAS. HOWEVER...AN AXIS OF STRONG
INSTABILITY AND WEAKENING CAP SHOULD DEVELOP INTO SERN ND/NERN SD
LATE THIS AFTERNOON. ATTM...POTENTIAL FOR DEVELOPMENT REMAINS
LIMITED AND WILL OPT TO KEEP CONDITIONAL LOW SEVERE PROBABILITIES
ALONG THE WARM FRONT.
HOWEVER...RESIDUAL MOISTURE AND NELY SURFACE FLOW SHOULD PREVAIL
INTO PARTS OF SRN/CENTRAL MT. HERE SURFACE DEW POINTS AROUND 50F
AND SUFFICIENT HEATING SHOULD SUPPORT AXIS OF MODERATE INSTABILITY
AND WEAK CAPPING AHEAD OF APPROACHING MID/UPPER LEVEL TROUGH. MOIST
CONVECTION SHOULD INCREASE IN COVERAGE AND INTENSITY THROUGH THE MID
TO LATE AFTERNOON OVER THE NRN ROCKIES...WITH SEVERE THREAT
INCREASING AS STORMS SPREAD EWD ACROSS LOWER ELEVATIONS LATE
TODAY/THIS EVENING. GIVEN ELY COMPONENT OF SURFACE FLOW AND 50 KT
WNWLY MID LEVEL WINDS...EFFECTIVE SHEAR VECTORS ARE FORECAST TO BE
QUITE STRONG. THIS SHOULD SUPPORT SUPERCELLS AND ORGANIZED
LINES/BOW ECHOES...ESPECIALLY ACROSS SOUTHERN MT WHERE MLCAPE VALUES
WILL BE GREATER. LARGE HAIL AND DAMAGING WINDS WILL BE PRIMARY
SEVERE THREATS. HOWEVER...IF DEW POINTS CAN HOLD IN THE LOWER/MID
50S THEN ISOLATED TORNADOES WILL ALSO BE POSSIBLE. ACTIVITY SHOULD
EVOLVE INTO ONE OR TWO MCSS AND SHIFT ENEWD OVERNIGHT INTO WRN
ND/NWRN SD...THOUGH SEVERE THREAT SHOULD WANE AFTER DARK.
..NRN MN INTO THE NRN GREAT LAKES...
STRONG LOW LEVEL WAA ALONG AND NORTHEAST OF SURFACE WARM FRONT IS
EXPECTED TO INCREASE STORMS LATER TODAY AND THIS EVENING INTO THE
RED RIVER VALLEY AND NRN MS. THIS WILL BE ASSOCIATED WITH SUBTLE
SHORTWAVE TROUGH FORECAST TO CREST THE UPPER RIDGE. FORECAST
SOUNDINGS SUGGEST ACTIVITY WILL REMAIN ELEVATED...THOUGH MODERATE TO
STRONG MUCAPE AND EFFECTIVE SHEAR FROM 40-50 KT SHOULD ENHANCE THE
ORGANIZATION/INTENSITY OF THIS ACTIVITY. STORMS SHOULD SPREAD
QUICKLY ESEWD AND BECOME INCREASINGLY ELEVATED THIS
EVENING/OVERNIGHT. LARGE HAIL IS EXPECTED TO BE PRIMARY SEVERE
THREAT...THOUGH ISOLATED DAMAGING WINDS MAY BE POSSIBLE IF STORMS
CAN ROOT NEAR THE SURFACE WARM FRONT.
..FL PENINSULA...
12Z SOUNDINGS INDICATE VERY STEEP LAPSE RATES AND H5 TEMPS FROM -10C
TO -12C OVER MUCH OF FL INVOF MID LEVEL COLD POCKET ASSOCIATED WITH
WEAKENING UPPER LOW NOW SHEARING APART JUST EAST OF FL. CLEAR SKIES
THIS MORNING WILL ALLOW ABUNDANT HEATING TO OCCUR AND SHOULD SUPPORT
MODERATE INSTABILITY THIS AFTERNOON. MAIN LIMITING FOR SEVERE IS
RELATIVELY DRY LOW LEVELS AND POSSIBILITY OF BOUNDARY LAYER MIXING
LOWERING SURFACE DEW POINTS /12Z SOUNDING AT TBW HAS DRIED
CONSIDERABLY OVER THE PAST 24 HRS IN THE LOW LEVELS/.
REGARDLESS...IT APPEARS ACTIVE SEA BREEZE/LAKE BREEZE CIRCULATIONS
AND SWD MOVING COLD FRONT INTO NRN FL SHOULD SUPPORT/FOCUS SCATTERED
TO NUMEROUS THUNDERSTORMS THIS AFTERNOON/EVENING...ESPECIALLY OVER
CENTRAL FL. COLD AIR ALOFT AND STEEP LAPSE RATES SHOULD SUPPORT
SOME LARGE HAIL...WHILE DRY SUB-CLOUD LAYER MAY ENHANCE THE WET
MICROBURST POTENTIAL WITH STRONGER CORES.
..CENTRAL HIGH PLAINS...
STEEP LAPSE RATES AND DEEP BOUNDARY LAYER MIXING SHOULD AGAIN
SUPPORT SCATTERED HIGH BASED THUNDERSTORMS WITHIN MARGINAL
INSTABILITY SPREADING ENEWD OFF THE CENTRAL ROCKIES. AN ISOLATED
STRONG GUST MAY ACCOMPANY THIS ACTIVITY INTO WRN SD/WRN NEB/NERN CO.
HOWEVER...OVERALL SEVERE THREAT SHOULD REMAIN LIMITED.
..CENTRAL GULF COAST INTO TX...
LAPSE RATES REMAIN RATHER STEEP ACROSS THIS REGION ATOP MOIST
BOUNDARY LAYER WITH SURFACE DEW POINTS IN THE MID/UPPER 60S. THIS
WILL ONCE AGAIN SUPPORT LARGE AREA OF MODERATE TO STRONG
INSTABILITY...WHICH IN TURN SHOULD ALLOW ISOLATED PULSE-SEVERE
STORMS TO FORM WITHIN WEAK SHEAR. ACTIVITY IS EXPECTED TO BE HIGHLY
DIURNAL IN NATURE WITH STORMS DIMINISHING AFTER DARK.
.EVANS/LEVIT.. 05/13/2007
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