SWODY1
SPC AC 181241
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0741 AM CDT MON AUG 18 2008
VALID 181300Z - 191200Z
...THERE IS A SLGT RISK OF SVR TSTMS LATER THIS AFTERNOON INTO EARLY
TONIGHT FOR NRN NY INTO NRN NEW ENGLAND...
...THERE IS A SLGT RISK OF SVR TSTMS THOUGH EARLY TUESDAY FOR S
FL...
...NRN NY INTO NRN NEW ENGLAND LATE THIS AFTERNOON INTO TONIGHT...
A PRONOUNCED MID LEVEL SHORTWAVE TROUGH WILL MOVE ESEWD OVER QUEBEC
TO NRN NEW ENGLAND BY LATE TONIGHT. THIS MID LEVEL TROUGH WILL BE
ACCOMPANIED BY A SURFACE COLD FRONT WHICH WILL REACH THE SAINT
LAWRENCE VALLEY THIS EVENING AND MOVE INTO NRN NEW ENGLAND
OVERNIGHT.
A BELT OF LOW-MID 60S BOUNDARY LAYER DEWPOINTS AND DAYTIME HEATING
WILL CONTRIBUTE TO SUFFICIENT INSTABILITY FOR DEEP CONVECTION TODAY
IN ADVANCE OF THE COLD FRONT AND MID LEVEL WAVE. MINIMAL CONVECTIVE
INHIBITION BY AFTERNOON SHOULD ALLOW THE DEVELOPMENT OF WIDELY
SCATTERED WARM SECTOR THUNDERSTORMS FROM CENTRAL/NRN NY INTO
INTERIOR NEW ENGLAND. A MORE CONCENTRATED BAND OF STORMS WILL
LIKELY FORM DURING THE AFTERNOON OVER ONTARIO/QUEBEC ALONG THE
FRONT...AND CROSS INTO NRN NY/NEW ENGLAND LATE THIS EVENING INTO
EARLY TONIGHT. STILL...VERTICAL SHEAR WILL BE RELATIVELY WEAK
DURING THE DAY IN THE WARM SECTOR...AND DEEP LAYER WINDS/VERTICAL
SHEAR WILL INCREASE PRIMARILY NEAR AND AFTER DARK AS INSTABILITY
WEAKENS. THEREFORE...THE DAMAGING WIND/HAIL THREAT DURING THE
AFTERNOON WILL BE RATHER MARGINAL ACROSS NEW ENGLAND AS A RESULT OF
WEAK VERTICAL SHEAR...WHILE UNCERTAINTIES PERSIST INTO TONIGHT SINCE
THE COLD FRONT WILL ARRIVE AFTER DARK AND AS THE BOUNDARY LAYER IS
STABILIZING.
...S FL THROUGH EARLY TUESDAY...
TROPICAL STORM FAY IS MOVING OFF THE NRN COAST OF CUBA THIS MORNING
AND IS FORECAST TO BECOME A MINIMAL HURRICANE BY EARLY TUESDAY AS IT
PASSES THE WRN FL KEYS AND APPROACHES THE SW FL COAST /SEE LATEST
NHC ADVISORIES FOR DETAILS/. THE STORM STRUCTURE IS A BIT
RAGGED/ASYMMETRIC WITH THE MAJORITY OF THE DEEP CONVECTION TO THE
E/NE OF CYCLONE CENTER. STILL...GIVEN THE EXPECTATION FOR SOME
STRENGTHENING AND CONTINUED NNW TO N MOVEMENT OF THE STORM...THE
ENVIRONMENT SHOULD GRADUALLY BECOME MORE FAVORABLE FOR OUTER
RAINBAND SUPERCELLS ACROSS S FL TODAY INTO TONIGHT.
...INTERIOR ORE/WA TODAY INTO EARLY TONIGHT...
A MID LEVEL SHORTWAVE TROUGH OFF THE NRN CA COAST WILL PIVOT NEWD TO
ORE BY LATE TODAY INTO TONIGHT...WHILE A SEPARATE/WEAKER WAVE MOVES
NNEWD FROM NE CA TO ERN ORE/SW ID TODAY. A PLUME OF LOW-MID LEVEL
MOISTURE IN ADVANCE OF THE PRIMARY TROUGH HAS SUPPORTED
THUNDERSTORMS OVERNIGHT ACROSS THE CASCADES...AS WELL AS NEAR THE
ORE COAST. THE RICHEST LOW-LEVEL MOISTURE WILL REMAIN LARGELY W OF
THE CASCADES TODAY...WHILE THE STRONGER SURFACE HEATING AND STEEPER
LAPSE RATES WILL RESIDE E OF THE CASCADES THIS AFTERNOON. THE NET
RESULT WILL BE SUFFICIENT INSTABILITY FOR A FEW STRONG/SEVERE STORMS
THIS AFTERNOON INTO EARLY TONIGHT...MAINLY NEAR AND IMMEDIATELY E OF
THE CASCADES. THERE WILL ALSO BE AN INCREASE IN DEEP LAYER VERTICAL
SHEAR WITH THE APPROACH OF THE PRIMARY MID LEVEL TROUGH...THUS A FEW
ORGANIZED MULTICELLS...AND PERHAPS A SUPERCELL OR TWO...COULD
PRODUCE ISOLATED LARGE HAIL AND DAMAGING GUSTS.
...W TX/SE NM TODAY...
THE PERSISTENT MID LEVEL LOW NOW OVER SE CO/NE NM WILL MOVE SLOWLY
SEWD TOWARD THE TX PANHANDLE THROUGH TONIGHT. THOUGH A WEAK FEED OF
STEEPER MID LEVEL LAPSE RATES SHOULD BE MAINTAINED FROM NRN AZ INTO
WRN/CENTRAL NM...THE NET EFFECT OF WIDESPREAD CONVECTION THE PAST
SEVERAL DAYS HAS BEEN TO REDUCE LAPSE RATES/INSTABILITY OVER MUCH OF
THE SRN HIGH PLAINS. THERE WILL STILL BE SOME POTENTIAL FOR POCKETS
OF MODERATE INSTABILITY THIS AFTERNOON WHERE SURFACE HEATING IS
STRONGEST /PRIMARILY ACROSS SW TX/SE NM/...AND EFFECTIVE BULK SHEAR
SHOULD APPROACH 30-35 KT OVER THIS SAME AREA. VERY ISOLATED
DAMAGING GUSTS AND LARGE HAIL COULD OCCUR TODAY INTO THIS EVENING
ACROSS W/SW TX AND SE NM...BUT THE OVERALL SEVERE STORM THREAT IS
TOO MARGINAL FOR MORE THAN LOW WIND/HAIL PROBABILITIES.
..THOMPSON/LEVIT.. 08/18/2008
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