SPC AC 041255
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0755 AM CDT WED JUL 04 2007
VALID 041300Z - 051200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE MIDDLE MS VALLEY INTO
THE MID ATLANTIC STATES...
...SYNOPSIS...
UPPER FLOW PATTERN IS FORECAST TO AMPLIFY SLIGHTLY THIS PERIOD AS
SHORT WAVE TROUGH MOVING SEWD ACROSS THE GREAT LAKES MOVES INTO THE
MEAN LONG WAVE TROUGH POSITION OVER ERN CANADA AND THE NERN US.
MEANWHILE...THE RIDGE OVER THE WESTERN STATES BUILDS IN THE WAKE OF
ANOTHER SHORT WAVE TROUGH CURRENTLY TURNING SEWD ACROSS
SASKATCHEWAN. THE UPPER LOW OVER TX IS EXPECTED TO MOVE LITTLE
THROUGH TONIGHT.
AT THE SURFACE...PRIMARY LOW WILL MOVE EWD FROM NERN ONTARIO INTO
QUEBEC AS TRAILING COLD FRONT MOVES ACROSS THE GREAT LAKES...MIDDLE
MS VALLEY...AND CENTRAL PLAINS. A WARM FRONT EXTENDING SSEWD FROM
ERN LOWER MI INTO WEST VA WILL MOVE EWD INTO NEW ENGLAND.
...MIDDLE MS VALLEY ACROSS LOWER GREAT LAKES INTO MIDDLE ATLANTIC
STATES...
BAND OF WEAKER CONVECTION EXTENDS FROM NY/PA WWD INTO INDIANA...WITH
STRONGER THUNDERSTORMS EXTENDING WWD OVER PARTS OF CENTRAL IL AND
NERN MO. THIS ACTIVITY IS ASSOCIATED WITH THE SHORT WAVE TROUGH
MOVING ACROSS THE GREAT LAKES...AND HAS GENERATED WIDESPREAD CLOUDS
WHICH ARE LIKELY TO LIMIT HEATING/DESTABILIZATION IN ADVANCE OF THE
SHORT WAVE TROUGH TODAY.
MOISTURE IS SPREADING ENEWD ACROSS THE OH VALLEY IN RESPONSE TO
WSWLY LOW LEVEL WINDS FROM THE OH VALLEY INTO THE MIDDLE ATLANTIC
REGION...WITH SURFACE DEW POINTS IN THE LOW/MID 60S OVER KY. AS THE
WSWLY LOW LEVEL JET STRENGTHENS TODAY MOISTURE IS EXPECTED TO
INCREASE INTO PA AND THE DELMARVA REGION WITH DEW POINTS REACHING
THE MID 60S DURING THE AFTERNOON. HOWEVER...THE EXTENT OF CLOUD
COVER ACROSS THE AREA WILL MODULATE THE MAGNITUDE OF INSTABILITY.
ATTM IT APPEARS THAT STRONGER HEATING WILL OCCUR OVER THE OH VALLEY
INTO NRN VA WHERE MLCAPE IS FORECAST TO RANGE FROM 1000 J/KG OVER
THE NRN VA AREA TO 1500-2000 J/KG OVER THE LOWER OH VALLEY AND SRN
IL.
SCATTERED THUNDERSTORMS ARE EXPECTED TO INCREASE IN COVERAGE AND
INTENSITY BY EARLY/MID AFTERNOON AS THE SHORT WAVE TROUGH PROGRESSES
ESEWD TOWARD THE MIDDLE ATLANTIC STATES AND NEW ENGLAND. NWLY MID
LEVEL WINDS OF 40-45 KT WILL RESULT IN DEEP LAYER SHEAR OF 35-45 KT
ACROSS THE UPPER OH VALLEY/LOWER GREAT LAKES AND MID ATLANTIC
STATES...WHICH WILL ENHANCE STORM ORGANIZATION AND INTENSITY.
ALTHOUGH UNCERTAINTY EXISTS REGARDING THE AMOUNT OF INSTABILITY THAT
WILL DEVELOP...STRENGTH OF DYNAMIC FORCING FOR LARGE SCALE ASCENT
AHEAD OF THE SHORT WAVE TROUGH SHOULD BE SUFFICIENT TO PROMOTE
CONVECTIVE STORMS...ESPECIALLY IN AREAS WHERE BREAKS IN CLOUD COVER
PERMIT STRONGER HEATING. GIVEN SUFFICIENT INSTABILITY AND THE
EXPECTED FAVORABLE SHEAR...A FEW SEVERE THUNDERSTORMS ARE POSSIBLE
WITH PRIMARY THREAT FOR DAMAGING WIND GUSTS AND OCCASIONAL HAIL.
OVER THE ERN PART OF THE RISK AREA...FORECAST WIND PROFILES EXHIBIT
CONSIDERABLE VEERING AND INCREASE IN SPEED WITH HEIGHT SUGGESTING
ENHANCED POTENTIAL FOR A FEW SUPERCELLS TO DEVELOP WITH AN
ASSOCIATED THREAT FOR ISOLATED TORNADOES. THE SEVERE THREAT SHOULD
CONTINUE THROUGH THE EVENING HOURS WITH STORMS SLOWLY DIMINISHING
THEREAFTER.
...LOWER MO VALLEY/CENTRAL PLAINS INTO PARTS OF NM/ERN CO...
STEEP LAPSE RATES COUPLED WITH AMPLE LOW LEVEL MOISTURE WILL
CONTRIBUTE TO UNSTABLE ENVIRONMENT WITH MLCAPE OF 1000-2000 J/KG
THIS AFTERNOON. CONVERGENCE ALONG THE FRONT AND/OR REMNANT OUTFLOW
BOUNDARIES COUPLED WITH STRONG DIABATIC HEATING WILL PROMOTE
DEVELOPMENT OF SCATTERED THUNDERSTORMS THIS AFTERNOON. UPSLOPE FLOW
OVER THE HIGH PLAINS AND THE ELEVATED HEATING SOURCE OVER THE
MOUNTAINS OF CO/NM WILL ALSO AID IN CONVECTIVE DEVELOPMENT. A FEW
STRONG/LOCALLY SEVERE STORMS ARE EXPECTED THIS AFTERNOON AND
EVENING...HOWEVER MINIMAL DYNAMIC FORCING AND WEAK VERTICAL SHEAR
ARE EXPECTED TO LIMIT OVERALL SEVERE COVERAGE.
...NERN ND/NRN MN...
SATELLITE IMAGERY SHOWS SHORT WAVE TROUGH OVER SRN SASKATCHEWAN
BEGINNING TO TURN ESEWD AFTER CROSSING THE UPPER RIDGE AXIS OVER
ALBERTA. VISIBLE SATELLITE SHOWS CLEAR SKIES OVER ND/MN WHICH
SHOULD ALLOW STRONG HEATING TO OCCUR TODAY. SURFACE DEW POINTS ARE
EXPECTED TO REMAIN IN THE 55-60F RANGE RESULTING IN MLCAPE OF
500-1000 J/KG THIS AFTERNOON AND EVENING. LITTLE IF ANY LOW LEVEL
CONVERGENCE IS EXPECTED TO AID CONVECTIVE DEVELOPMENT.
HOWEVER...LARGE SCALE ASCENT ASSOCIATED WITH THE SHORT WAVE TROUGH
SHOULD BE SUFFICIENT FOR WIDELY SCATTERED THUNDERSTORMS TO FORM OVER
SRN MANITOBA AND SPREAD SEWD INTO NERN ND/NRN MN LATER THIS
AFTERNOON AND EVENING. STEEP LOW LEVEL LAPSE RATES AND 40 KT DEEP
LAYER SHEAR SUGGEST POTENTIAL FOR ISOLATED SEVERE STORMS WITH
PRIMARY THREAT FOR LARGE HAIL AND STRONG WIND GUSTS.
..WEISS/GUYER.. 07/04/2007
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
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