SWODY1
SPC AC 160537
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1237 AM CDT SAT AUG 16 2008
VALID 161200Z - 171200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
A SIGNIFICANT IMPULSE AND ASSOCIATED EMBEDDED CIRCULATION WITHIN THE
LARGE SCALE EASTERN U.S. UPPER TROUGH IS NOW BEGINNING TO SHIFT EAST
OF THE LOWER GREAT LAKES REGION. THIS APPEARS TO BE OCCURRING IN
RESPONSE TO THE APPROACH OF A STRONG DIGGING SHORT WAVE
TROUGH...WITHIN THE MAIN BELT OF THE POLAR WESTERLIES ACROSS THE
HUDSON/JAMES BAY VICINITY. AS THE LATTER FEATURE CONTINUES EASTWARD
THROUGH QUEBEC...MODELS INDICATE THAT THE FORMER SYSTEM WILL
PROGRESS ACROSS THE NEW ENGLAND COAST EARLY TODAY...BEFORE
ACCELERATING NORTHEASTWARD...EAST OF THE CANADIAN MARITIMES BY 12Z
SUNDAY. IN ITS WAKE...MID/UPPER FLOW IS PROGGED TO WEAKEN
CONSIDERABLY ACROSS MUCH OF THE EASTERN U.S...BUT IT WILL LIKELY
REMAIN BROADLY CYCLONIC...WITH LINGERING LOW AMPLITUDE TROUGHING
CENTERED OVER THE SOUTHEASTERN STATES.
MEANWHILE...MODELS INDICATE THAT AN UPPER RIDGE WILL REMAIN STRONG
ACROSS MUCH OF THE PACIFIC COAST STATES AND INTERMOUNTAIN REGION
THROUGH THE FIRST HALF OF THE PERIOD...BEFORE BEGINNING TO WEAKEN
LATE AS A SIGNIFICANT UPPER TROUGH GRADUALLY APPROACHES THE COAST.
AS A RESULT...THE CUT-OFF LOW OVER THE CENTRAL ROCKIES IS EXPECTED
TO MOVE LITTLE...EXCEPT FOR PERHAPS A SLIGHT SOUTHEASTWARD SHIFT IN
RESPONSE TO A SIGNIFICANT IMPULSE PIVOTING AROUND ITS SOUTHERN/
EASTERN PERIPHERY.
...SOUTHERN PLATEAU INTO THE SOUTHERN PLAINS RIO GRANDE VALLEY...
DUE TO THE EVOLVING UPPER PATTERN...STEEPER LAPSE RATES AND
POTENTIAL FOR STRONGER HEATING ARE BECOMING CONFINED TO AREAS WEST
OF THE CONTINENTAL DIVIDE. A FEW STRONG/LOCALLY SEVERE STORMS WILL
BE POSSIBLE IN THIS REGION AS CONVECTION INITIATES ACROSS THE HIGHER
TERRAIN DURING AND SHORTLY AFTER THE PEAK AFTERNOON HEATING.
ADDITIONAL STRONG/SEVERE STORMS ARE POSSIBLE TO THE IMMEDIATE LEE OF
THE MOUNTAINS OF CENTRAL NEW MEXICO...WHERE A MOIST UPSLOPE FLOW
WILL PERSIST BENEATH MODEST NORTHWEST FLOW ALOFT.
FARTHER EAST...CONVECTIVE POTENTIAL IS CONSIDERABLY MORE UNCERTAIN.
MID-LEVEL LAPSE RATES ACROSS THE TEXAS SOUTH PLAINS/EDWARDS PLATEAU
AND HILL COUNTRY WILL BE WEAK. BUT...THERE IS CONCERN THAT A
PERTURBATION ASSOCIATED WITH AN ONGOING STORM CLUSTER NOW
APPROACHING THE TEXAS SOUTH PLAINS COULD SUPPORT NEW STORM
DEVELOPMENT LATER TODAY ACROSS PARTS OF SOUTH CENTRAL TEXAS.
LOW-LEVELS ARE EXPECTED TO BE MOISTENING ON LIGHT SOUTHEASTERLY
LOW-LEVEL FLOW. AND...DEEP LAYER SHEAR BENEATH WEAK TO MODERATE
WESTERLY MID/HIGH LEVEL FLOW COULD BECOME SUFFICIENT FOR AT LEAST
SHORT-LIVED SUPERCELLS...IF BOUNDARY LAYER DESTABILIZATION BECOMES
GREATER THAN CURRENTLY ANTICIPATED.
...UPPER GREAT LAKES REGION...
DESTABILIZATION AND LIFT...ASSOCIATED WITH WARM ADVECTION ON THE
NOSE OF AN ELEVATED MIXED LAYER EMANATING FROM THE CANADIAN/
NORTHERN U.S. ROCKIES REGION...COULD BECOME SUFFICIENT FOR SCATTERED
THUNDERSTORMS ACROSS PARTS OF UPPER MICHIGAN AND NORTHERN WISCONSIN
LATE THIS AFTERNOON. IF THIS OCCURS...THERMODYNAMIC PROFILES WITHIN
A MODERATELY SHEARED NORTHWEST FLOW PROBABLY WILL BE SUPPORTIVE OF A
MARGINALLY SEVERE HAIL/WIND GUST THREAT.
...ATLANTIC SEABOARD...
IT NOW APPEARS THAT LOWER/MID TROPOSPHERIC DRYING/SUBSIDENCE WILL
OVERSPREAD MUCH OF NORTHERN MID ATLANTIC AND NEW ENGLAND COASTAL
AREAS BY MIDDAY. THIS WILL PROBABLY SUPPRESS CONVECTIVE POTENTIAL
TODAY.
LINGERING MOISTURE/INSTABILITY ACROSS THE CAROLINA PIEDMONT AND
COASTAL AREAS COULD REMAIN SUFFICIENT FOR VIGOROUS CONVECTIVE
DEVELOPMENT AS WEAK FORCING ON THE TAIL END OF THE UPPER TROUGH
OVERSPREADS THE REGION DURING THE AFTERNOON/EVENING HOURS.
OTHERWISE...THE HIGHEST PROBABILITY FOR THUNDERSTORM ACTIVITY
APPEARS TO EXIST ACROSS THE FLORIDA PENINSULA...WHERE BOUNDARY LAYER
MOISTURE CONTENT REMAINS HIGH...MID-LEVEL INHIBITION REMAINS
WEAK...AND INLAND ADVANCING SEA BREEZES WILL PROVIDE A FOCUS FOR
INITIATION.
..KERR/LEVIT.. 08/16/2008
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