DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 131632
SWODY1
SPC AC 131630

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1130 AM CDT TUE AUG 13 2013

VALID 131630Z - 141200Z

...THERE IS A SLGT RISK OF SVR TSTMS TODAY ACROSS PARTS OF THE MID
ATLANTIC COAST REGION...

...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTERNOON AND EVENING
ACROSS PARTS OF THE NORTHERN HIGH PLAINS...

...SYNOPSIS...
WITHIN A SOMEWHAT AMPLIFIED CYCLONIC MID-LEVEL FLOW REGIME...NOW
ENCOMPASSING MUCH OF EASTERN NORTH AMERICA...A VIGOROUS SHORT WAVE
TROUGH IS FORECAST TO DIG SOUTHEAST OF THE UPPER GREAT LAKES REGION
DURING THE DAY...BEFORE TURNING EASTWARD ACROSS THE LOWER GREAT
LAKES REGION...TOWARD THE NORTHERN ATLANTIC COAST TONIGHT. AS THIS
OCCURS...AN INTRUSION OF SUBSTANTIVELY COOLER AND DRIER LOW-LEVEL
AIR WILL CONTINUE TO ADVANCE SOUTHEAST OF THE UPPER MIDWEST AND
GREAT LAKES REGION...WITH THE COLD FRONT LIKELY TO REACH THE
SOUTHERN MID ATLANTIC COAST STATES...TENNESSEE VALLEY AND OZARKS
PLATEAU BY 12Z WEDNESDAY.

AT THE SAME TIME...THE CONVECTIVELY REINFORCED REMNANTS OF A
PRECEDING FRONT WILL CONTINUE TO ADVANCE SLOWLY SOUTHWARD THROUGH
THE GULF COAST STATES AND SOUTH CENTRAL INTO SOUTHERN PLAINS...
GENERALLY TO THE SOUTH OF A BELT OF SEASONABLY STRONG HIGH LEVEL
FLOW ON THE NORTHERN PERIPHERY OF FLAT SUBTROPICAL RIDGING.
MID-LEVEL RIDGING TO THE NORTH OF THIS LATTER FEATURE...ACROSS MUCH
OF THE INTERMOUNTAIN WEST INTO THE PLAINS...MAY BEGIN TO WEAKEN IN
RESPONSE TO SEVERAL WEAK IMPULSES PROGRESSING AROUND ITS
CREST...ACROSS THE NORTHERN ROCKIES...IN ADVANCE OF A SIGNIFICANT
CLOSED LOW APPROACHING THE PACIFIC NORTHWEST COAST.

IN RESPONSE TO THESE DEVELOPMENTS...SEASONABLY HIGH MOISTURE CONTENT
AIR HAS BECOME CONFINED TO PORTIONS OF THE LOWER SOUTHERN PLAINS
INTO THE CENTRAL AND EASTERN GULF STATES...AS WELL AS PORTIONS OF
THE MID ATLANTIC COAST. AND STEEP MID-LEVEL LAPSE RATES...EAST OF
THE ROCKIES...REMAIN CONFINED TO PORTIONS OF THE NORTHERN PLAINS.
SOME STEEPENING OF LAPSE RATES WILL OCCUR WITH STRONG MID-LEVEL
COOLING ACCOMPANYING THE GREAT LAKES TROUGH...BUT THIS WILL BE
MOSTLY POST-FRONTAL.

...SOUTHERN NEW ENGLAND INTO MID ATLANTIC COAST STATES...
THE POTENTIALLY MOST SUBSTANTIVE SEVERE WEATHER THREAT FOR THE DAY
APPEARS TO HAVE DIMINISHED/SHIFTED EAST OF NORTHERN MID ATLANTIC
COASTAL AREAS THIS MORNING. IN ADVANCE OF THE GREAT LAKES UPPER
TROUGH...A LOWER AMPLITUDE IMPULSE...WITH A BELT OF ENHANCED
LOWER/MID TROPOSPHERIC FLOW...HAS SHIFTED OFFSHORE. ASSOCIATED
ORGANIZED STRONG/SEVERE STORM DEVELOPMENT...INCLUDING
SUPERCELLS...APPEARS INCREASINGLY CERTAIN TO REMAIN SOUTH OF
SOUTHERN NEW ENGLAND COASTAL AREAS. HOWEVER...MODELS DO CONTINUE TO
INDICATE THAT A SECONDARY SURFACE LOW WILL FORM IN ASSOCIATION WITH
THE APPROACHING TROUGH...AND MIGRATE NORTHEASTWARD ACROSS PARTS OF
SOUTHERN NEW ENGLAND LATER TODAY AND TONIGHT. IF THIS
OCCURS...FAVORABLY TIMED WITH AT LEAST SOME BOUNDARY LAYER HEATING
AND DESTABILIZATION...IT STILL DOES NOT APPEAR OUT OF THE QUESTION
THAT THE ENVIRONMENT MAY BECOME SUPPORTIVE OF AT LEAST LOW SEVERE
THUNDERSTORM POTENTIAL.

FARTHER TO THE SOUTH AND WEST...VEERING AND WEAKENING OF LOW/MID
LEVEL WIND FIELDS APPEAR TO BE ENDING LOW TORNADIC POTENTIAL.
HOWEVER...THE PRE-FRONTAL ENVIRONMENT REMAINS SEASONABLY MOIST
ACROSS MUCH OF EASTERN NORTH CAROLINA AND SOUTHEAST VIRGINIA INTO
THE DELMARVA PENINSULA...WHERE INSOLATION IS SUPPORTING MODERATELY
LARGE CAPE. ALTHOUGH DEEP LAYER FLOW AND SHEAR ARE WEAKENING...THEY
MAY REMAIN STRONG ENOUGH TO SUPPORT SLIGHT RISK SEVERE
PROBABILITIES...THOUGH FORCING FOR ORGANIZED CONVECTIVE DEVELOPMENT
IS BECOMING INCREASINGLY UNCLEAR.

...NORTHERN HIGH PLAINS...
BENEATH STEEP MID-LEVEL LAPSE RATES...SOUTHEASTERLY LOW-LEVEL FLOW
IS EXPECTED TO MAINTAIN SUFFICIENT LOW-LEVEL MOISTURE TO SUPPORT AT
LEAST MODERATE CAPE BY LATE AFTERNOON. ALTHOUGH SHEAR IS EXPECTED
TO REMAIN GENERALLY WEAK TO MODEST IN
STRENGTH...FORCING...ASSOCIATED WITH WEAK PERTURBATIONS/CYCLONIC
VORTICITY MAXIMA ROUNDING THE UPPER RIDGE...MAY CONTRIBUTE TO ONE OR
TWO SMALL STORM CLUSTERS CAPABLE OF GENERATING SEVERE WIND
GUSTS...IN ADDITION TO HAIL.

..KERR/COHEN.. 08/13/2013

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