SWODY1
SPC AC 260525
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1225 AM CDT FRI AUG 26 2011
VALID 261200Z - 271200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
MODELS INDICATE LITTLE CHANGE TO THE LARGE-SCALE PATTERN THROUGH
THIS FORECAST PERIOD. THE POLAR JET WILL REMAIN CONFINED TO AREAS
NEAR/NORTH OF THE CANADIAN/U.S. BORDER...WITH A SIGNIFICANT EMBEDDED
SHORT WAVE TROUGH LIKELY TO DIG ACROSS MANITOBA AND NORTHERN
ONTARIO...BEFORE TURNING EASTWARD TOWARD QUEBEC. AS THIS
OCCURS...AND AS A BELT OF STRONGER FLOW PROPAGATES AROUND THE
NORTHERN AND EASTERN PERIPHERY OF THE FOUR CORNERS SUBTROPICAL
RIDGE...HURRICANE IRENE IS EXPECTED TO ACCELERATE ACROSS THE
SOUTHWESTERN ATLANTIC...TOWARD THE NORTH CAROLINA COAST.
...ATLANTIC COAST STATES...
THE PRIMARY FOCUS FOR THUNDERSTORM ACTIVITY TODAY MAY BE A REMNANT
FRONTAL ZONE EXTENDING FROM THE LEE OF THE CENTRAL APPALACHIANS
THROUGH NORTHERN VIRGINIA AND THE NORTHERN DELMARVA PENINSULA
THROUGH THE SOUTHERN NEW JERSEY COAST. MODEST DESTABILIZATION MAY
OCCUR ALONG THIS CORRIDOR WITH INSOLATION... BUT PROBABLY NOT
SUFFICIENT...GIVEN WEAK DEEP LAYER MEAN FLOW FIELDS AND SHEAR...TO
SUPPORT AN APPRECIABLE SEVERE WEATHER THREAT.
FARTHER SOUTH...LOW-LEVEL HODOGRAPHS COULD BECOME SIZABLE AND
CLOCKWISE CURVED BY EARLY EVENING ACROSS PARTS OF EASTERN NORTH
CAROLINA...BEFORE CONTINUING TO ENLARGE AND GROW INCREASINGLY
SUPPORTIVE OF TORNADIC POTENTIAL THROUGH THE 27/06-12Z TIME FRAME.
BOUNDARY LAYER DESTABILIZATION SUPPORTIVE OF THIS
THREAT...HOWEVER...REMAINS MORE UNCERTAIN. AN ISOLATED TORNADO MAY
NOT BE COMPLETELY OUT OF THE QUESTION ACROSS THE OUTER BANKS AND
COASTAL AREAS WITH CONVECTION DEVELOPING WELL IN ADVANCE OF IRENE.
HOWEVER...SOMEWHAT BETTER POTENTIAL SEEMS LIKELY TO AWAIT THE
NORTHWARD/INLAND ADVECTION OF THE RICHER TROPICAL BOUNDARY LAYER
MOISTURE...IN THE RIGHT FRONT QUADRANT OF THE NORTHWARD MOVING
CYCLONIC CIRCULATION CENTER. BASED ON THE CURRENT FORECAST
TRACK...THIS MAY NOT OCCUR UNTIL CLOSE TO 12Z SATURDAY AT THE
EARLIEST.
...UPPER GREAT LAKES REGION...
MODELS SUGGEST THAT MODEST BOUNDARY LAYER DESTABILIZATION IS
POSSIBLE THIS AFTERNOON AHEAD OF A COLD FRONT ASSOCIATED WITH THE
CANADIAN SHORT WAVE TROUGH. AND A 50+ KT 500 MB JET IS PROGGED TO
NOSE ACROSS THE UPPER PENINSULA OF MICHIGAN ON THE SOUTHERN
PERIPHERY OF THE UPPER IMPULSE...CONTRIBUTING TO STRONG VERTICAL
SHEAR. HOWEVER...STRONGER MID/UPPER FORCING FOR UPWARD VERTICAL
MOTION APPEARS LIKELY TO PASS WELL TO THE NORTH OF THE
REGION...WHICH PROBABLY WILL LIMIT THE THREAT TO AN ISOLATED
STRONG/SEVERE STORM OR TWO.
...MONTANA...
DESPITE THE LIKELY PRESENCE OF STEEP LAPSE RATES...IT REMAINS
UNCERTAIN WHETHER MOISTURE LEVELS WILL SUPPORT CAPE SUFFICIENT FOR
ANYTHING BEYOND MARGINAL/LOW SEVERE PROBABILITIES FOR THIS PERIOD.
HOWEVER...A SHORT WAVE IMPULSE EXPECTED TO PROGRESS ACROSS THE
MOUNTAINS OF WESTERN MONTANA LATE THIS AFTERNOON AND EVENING WILL BE
ACCOMPANIED BY FAVORABLE FORCING FOR CONVECTIVE DEVELOPMENT. THIS
COULD INCLUDE A POTENTIALLY ORGANIZED CLUSTER OF STORMS THAT MAY
CONTINUE ACROSS SOUTH CENTRAL/SOUTHEASTERN MONTANA TONIGHT...IN THE
PRESENCE OF STRONG VERTICAL SHEAR.
...CENTRAL HIGH PLAINS...
MODELS SUGGEST THAT AN UPPER IMPULSE EMERGING FROM THE SOUTHWESTERN
MONSOONAL REGIME...AND PROGRESSING AROUND THE PERIPHERY OF THE
SUBTROPICAL HIGH CENTER...COULD ENHANCE CONVECTIVE POTENTIAL ACROSS
THE REGION LATE THIS AFTERNOON AND EVENING. STRONG HEATING AND
MOISTENING UPSLOPE FLOW MAY CONTRIBUTE TO A DEEPLY MIXED BOUNDARY
LAYER WITH SIZABLE CAPE... SUPPORTIVE OF VIGOROUS STORM DEVELOPMENT
CAPABLE OF PRODUCING LOCALLY STRONG DOWNBURSTS AND EXPANDING SURFACE
COLD POOLS WITH GUSTY WINDS.
..KERR/GARNER.. 08/26/2011
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