Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 270553
SWODY1
SPC AC 270551

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1251 AM CDT WED MAY 27 2015

VALID 271200Z - 281200Z

...THERE IS A SLGT RISK OF SVR TSTMS TODAY ACROSS PARTS OF THE MID
ATLANTIC COAST STATES INTO NORTHERN NEW ENGLAND...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE UPPER OHIO
VALLEY AND LOWER GREAT LAKES REGION...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CENTRAL
HIGH PLAINS INTO SOUTHERN PLAINS...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS SURROUNDING AREAS OF THE
CENTRAL HIGH PLAINS AND SOUTHERN PLAINS...THE LOWER MISSISSIPPI
VALLEY AND OHIO VALLEY...GULF COAST...AND THE PIEDMONT OF THE MID
AND SOUTHERN ATLANTIC COAST...

...SUMMARY...
A FEW SEVERE STORMS ARE POSSIBLE TODAY ACROSS PARTS OF THE NORTHERN
MID ATLANTIC COAST REGION INTO NORTHERN NEW ENGLAND...AS WELL AS
PARTS OF THE UPPER OHIO VALLEY AND LOWER GREAT LAKES REGION...AND
PORTIONS OF THE CENTRAL HIGH PLAINS INTO THE SOUTHERN PLAINS.

...SYNOPSIS...
IN THE WAKE OF A SIGNIFICANT SHORT WAVE IMPULSE EXPECTED TO TURN
EAST OF THE UPPER MIDWEST...AND PROGRESS THROUGH THE LOWER GREAT
LAKES REGION DURING THIS FORECAST PERIOD...WEST SOUTH WESTERLY
MID/UPPER FLOW IS EXPECTED TO BECOME SEASONABLY WEAK TO MODEST FROM
THE ROCKIES THROUGH THE MISSISSIPPI VALLEY.  IT ALSO APPEARS LIKELY
TO BECOME BROADLY ANTICYCLONIC...THOUGH WITH A NUMBER OF PROGRESSIVE
EMBEDDED SMALLER SCALE PERTURBATIONS.  TO THE SOUTHEAST OF THIS
REGIME...MODELS INDICATE THAT SUBTROPICAL RIDGING WILL BECOME MORE
PROMINENT ACROSS MUCH OF THE GULF COAST STATES...TENNESSEE VALLEY
AND SOUTH ATLANTIC COAST REGION.  TO THE WEST AND NORTHWEST...WITHIN
SEPARATE BELTS OF WESTERLIES EMANATING FROM THE PACIFIC...A COUPLE
OF NOTABLE SHORT WAVE IMPULSES ARE EXPECTED TO REMAIN SLOWLY
PROGRESSIVE.  ONE...WITH A BROAD EMBEDDED CLOSED LOW...IS FORECAST
TO DIG ACROSS THE NORTHERN INTERMOUNTAIN REGION AND ROCKIES.  THE
OTHER IS FORECAST TO PROGRESS INLAND ACROSS PARTS OF THE SOUTHWEST
U.S. AND NORTHWESTERN MEXICO.

IN LOWER-LEVELS...AS A MODEST SURFACE CYCLONE REDEVELOPS
NORTHEASTWARD ACROSS EASTERN CANADA...A WEAK SURFACE FRONT MAY
ADVANCE SOUTHEAST OF THE UPPER GREAT LAKES REGION.  THE TRAILING
WESTERN FLANK OF THIS FRONT ACROSS THE CENTRAL PLAINS MAY BE
ILL-DEFINED...WITH THE AIR MASS IN AT LEAST A COUPLE OF AREAS TO THE
SOUTH IMPACTED CONSIDERABLY BY ONGOING CONVECTION.  MODELS SUGGEST
THAT THE MOST SIGNIFICANT BAROCLINIC ZONE...PRIMARILY ASSOCIATED
WITH DIFFERENTIAL SURFACE HEATING...MAY DEVELOP ACROSS THE CENTRAL
HIGH PLAINS SOUTHEASTWARD INTO THE SOUTHERN PLAINS RED RIVER VALLEY
BY EARLY THIS AFTERNOON.

IT DOES APPEAR INCREASINGLY PROBABLE THAT A REMNANT AREA OF
CONVECTION AND ASSOCIATED COLD POOL MAY ADVANCE ACROSS SOUTHEAST
TEXAS INTO CENTRAL GULF COASTAL AREAS EARLY IN THE PERIOD.  IT IS
POSSIBLE THAT ANOTHER AREA OF CONVECTION COULD LINGER ACROSS PARTS
OF THE OZARK PLATEAU.  POTENTIAL FOR SUBSEQUENT REGENERATION OF
VIGOROUS CONVECTIVE DEVELOPMENT WITH BOTH THESE FEATURES REMAINS
UNCLEAR. THE AIR MASS ACROSS THE CENTRAL GULF COAST AND LOWER
MISSISSIPPI VALLEY REGION SHOULD BE MOIST WITH MODERATELY LARGE CAPE
DEVELOPING WITH DAYTIME HEATING.  BUT...ASIDE FROM A SPEED MAXIMUM
OR TWO ASSOCIATED WITH POSSIBLE CONVECTIVELY GENERATED MID-LEVEL
VORTICES...DEEP LAYER FLOW FIELDS SHOULD OTHERWISE BE RATHER WEAK.

ACROSS THE ATLANTIC SEABOARD...PRE-FRONTAL SURFACE TROUGHING TO THE
EAST OF THE APPALACHIANS MAY BECOME A FOCUS FOR SUBSTANTIVE
DESTABILIZATION ASSOCIATED WITH BOUNDARY LAYER MOISTENING AND
DAYTIME HEATING.

...UPPER OH VALLEY/GREAT LAKES AND MID ATLANTIC/NEW ENGLAND...
TO THE SOUTHEAST OF THE SHORT WAVE TROUGH CROSSING THE GREAT LAKES
REGION...30-50 KT SOUTHWESTERLY LOWER/MID TROPOSPHERIC FLOW IS
EXPECTED TO ENHANCE CONVECTIVE POTENTIAL ALONG AND AHEAD OF THE COLD
FRONT...AND NEAR THE PRE-FRONTAL TROUGH.  ORGANIZED LINES AND
CLUSTERS OF STORMS APPEAR POSSIBLE AS SURFACE HEATING CONTRIBUTES TO
WEAK TO MODERATE BOUNDARY LAYER DESTABILIZATION.  POTENTIALLY
DAMAGING WIND GUSTS ARE EXPECTED TO BE THE PRIMARY THREAT...THOUGH
IT APPEARS THAT THERMODYNAMIC PROFILES COULD BECOME CONDUCIVE TO
MARGINALLY SEVERE HAIL ACROSS THE UPPER OHIO VALLEY/LOWER GREAT
LAKES REGION.  DEEP LAYER MEAN FLOW ALONG THE LEE SURFACE TROUGH
ACROSS THE NORTHERN MID ATLANTIC COAST REGION PROBABLY WILL BE
WEAKER THAN AREAS TO THE NORTHWEST AND NORTH...BUT SOMEWHAT BETTER
INSTABILITY MAY COMPENSATE.

...CENTRAL HIGH PLAINS INTO SOUTHERN PLAINS...
FORECAST GUIDANCE IS SUGGESTIVE THAT THE AFOREMENTIONED DIFFERENTIAL
HEATING ZONE MAY BECOME THE FOCUS FOR SCATTERED VIGOROUS CONVECTIVE
DEVELOPMENT BY EARLY THIS AFTERNOON.  IN THE PRESENCE OF
THERMODYNAMIC PROFILES WITH STEEP MID-LEVEL LAPSE RATES AND MODERATE
TO LARGE CAPE...VEERING OF WEAK TO MODEST WIND FIELDS WITH HEIGHT
MAY CONTRIBUTE TO SUFFICIENT SHEAR FOR ISOLATED SUPERCELL STRUCTURES
BY LATE AFTERNOON.  LARGE HAIL...STRONG WIND GUSTS AND ISOLATED
TORNADOES MAY ALL BE POSSIBLE WITH STRONGEST STORMS...BEFORE
ACTIVITY WEAKENS IN WANING INSTABILITY THIS EVENING.

..KERR/PICCA.. 05/27/2015



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