Severe Storm Outlook Narrative (AC)
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ACUS02 KWNS 080459
SWODY2
SPC AC 080458

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1158 PM CDT TUE JUL 07 2015

VALID 091200Z - 101200Z

...THERE IS A MRGL RISK OF SVR TSTMS LATE THURSDAY AFTERNOON AND
EVENING ACROSS PARTS OF THE NORTHERN MID ATLANTIC COAST REGION...

...SUMMARY...
STRONG THUNDERSTORMS APPEAR POSSIBLE ACROSS THE NORTHERN MID
ATLANTIC COAST REGION ON THURSDAY.  THIS MAY INCLUDE AN EVOLVING
CLUSTER OF STORMS THAT COULD IMPACT THE URBAN CORRIDOR FROM
WASHINGTON D.C. TO PHILADELPHIA BY EARLY THURSDAY EVENING...WITH THE
RISK FOR POTENTIALLY DAMAGING WIND GUSTS.

...SYNOPSIS...
AS ITS CENTER SHIFTS WESTWARD ACROSS THE GULF COAST STATES...MODELS
CONTINUE TO INDICATE THAT SUBSTANTIAL EXPANSION OF SUBTROPICAL
RIDGING WILL OCCUR DURING THIS PERIOD...WESTWARD THROUGH THE LOWER
RIO GRANDE VALLEY AND ADJACENT NORTHERN MEXICO...AND NORTHWARD
THROUGH THE SOUTHERN/CENTRAL PLAINS AND MIDDLE MISSISSIPPI VALLEY.
THIS IS FORECAST COINCIDENT WITH THE SLOW INLAND ACCELERATION OF A
CLOSED LOW WITHIN THE SOUTHERN BRANCH OF SPLIT MID-LATITUDE
WESTERLIES...ACROSS THE CALIFORNIA COAST AND THE SIERRA NEVADA INTO
THE GREAT BASIN.

DESPITE MODEST STRENGTHENING OF SOUTHWESTERLY MID-LEVEL FLOW ACROSS
THE COLORADO VALLEY INTO THE SOUTHERN GREAT BASIN ASSOCIATED WITH
THE INLAND PROGRESSION OF THE UPPER LOW...RELATIVELY LOW MOISTURE
CONTENT ACROSS THESE SAME AREAS STILL APPEARS LIKELY TO LIMIT THE
MAGNITUDE OF DESTABILIZATION AND ASSOCIATED SEVERE WEATHER
POTENTIAL.  EAST OF THE ROCKIES...HIGHER MOISTURE CONTENT GENERALLY
WILL REMAIN CONFINED TO AREAS SOUTH OF THE STRONGER WESTERLIES.
AND...WITH THE POSSIBLE EXCEPTION OF THE NORTHERN MID ATLANTIC
COAST...WEAK MID-LEVEL LAPSE RATES DUE TO A WARMING MID/UPPER LEVEL
ENVIRONMENT...COUPLED WITH WEAK SHEAR...PROBABLY WILL MINIMIZE
SEVERE WEATHER POTENTIAL.

...NORTHERN MID ATLANTIC COAST...
MODELS STILL INDICATE THAT A CONVECTIVELY GENERATED OR ENHANCED
PERTURBATION EMERGING FROM THE SOUTHERN PLAINS...WITH AT LEAST A
MODESTLY STRONG BELT OF LOWER/MID TROPOSPHERIC FLOW...WILL
OVERSPREAD THE CENTRAL APPALACHIANS AND NORTHERN MID ATLANTIC COAST
REGION THURSDAY/THURSDAY NIGHT.  THE NAM AND ECMWF BOTH SUGGEST THAT
AN AREA OF ENHANCED UPWARD VERTICAL MOTION MAY BEGIN DEVELOPING
ACROSS AND EAST OF THE EASTERN WEST VIRGINIA PANHANDLE REGION BY
AROUND 09/21Z...ALONG AND PERHAPS JUST SOUTH OF A REMNANT FRONTAL
ZONE EXTENDING EASTWARD INTO COASTAL AREAS.

NEAR THE FRONT AND LEE TROUGH INTERSECTION...FAIRLY STRONG HEATING
INTO THE 90S MAY BECOME JUXTAPOSED WITH HIGH BOUNDARY LAYER MOISTURE
CONTENT CHARACTERIZED BY AT LEAST LOWER 70S F SURFACE DEW POINTS.
IF THIS OCCURS...MIXED LAYER CAPE MAY REACH 2000+ J/KG...DESPITE
RELATIVELY WARM MID-LEVEL TEMPERATURES.  COUPLED WITH STRENGTHENING
OF MEAN LOWER/MID TROPOSPHERIC WIND FIELDS TO 30+ KT...PERHAPS
INCLUDING A 40-50 KT SPEED MAXIMUM...IT APPEARS THAT THE ENVIRONMENT
MAY BECOME CONDUCIVE TO THE EVOLUTION OF AN ORGANIZED CONVECTIVE
CLUSTER CAPABLE OF PRODUCING DAMAGING WIND GUSTS...THROUGH HEAVY
PRECIPITATION LOADING AND DOWNWARD MIXING OF HIGHER MOMENTUM TO THE
SURFACE.  ACTIVITY MAY PROGRESS ACROSS THE URBAN CORRIDOR FROM
WASHINGTON D.C. TO PHILADELPHIA AROUND THE 10/00-03Z TIME
FRAME...BEFORE WEAKENING/PROGRESSING OFF COASTAL AREAS.

..KERR.. 07/08/2015




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