SWODY1
SPC AC 250529
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1229 AM CDT SUN SEP 25 2011
VALID 251200Z - 261200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON AND EVENING
ACROSS SOUTHERN/EASTERN ARKANSAS AND ADJACENT PORTIONS OF THE LWR MS
VALLEY...
...SYNOPSIS...
MODELS INDICATE THAT A SIGNIFICANT SHORT WAVE TROUGH WITHIN THE MAIN
BELT OF WESTERLIES WILL LIFT INLAND ACROSS THE PACIFIC NORTHWEST AND
CANADIAN ROCKIES DURING THIS FORECAST PERIOD. THIS FEATURE IS
PROGGED TO WEAKEN AS IT DOES...AS A STRONGER UPSTREAM IMPULSE FORMS
OVER THE EASTERN PACIFIC...AND A DOWNSTREAM RIDGE BUILDS ACROSS THE
CENTRAL CANADIAN PROVINCES. AS THIS LATTER DEVELOPMENT OCCURS...THE
CUT-OFF LOW NEAR THE MIDDLE MISSISSIPPI VALLEY IS EXPECTED TO REMAIN
QUASI-STATIONARY...WITH ONLY SUBTLE SHIFTS TO THE POSITION OF THE
CIRCULATION CENTER IN RESPONSE TO SHORT WAVE IMPULSES ROTATING
AROUND ITS PERIPHERY.
SOUTH AND EAST OF THE CLOSED LOW...HIGH MOISTURE CONTENT AIR
/CHARACTERIZED BY PRECIPITABLE WATER IN EXCESS OF TWO INCHES/ WILL
CONTINUE TO ADVECT NORTHWARD IN A NARROWING PLUME ON THE WESTERN
FRINGE OF AN ATLANTIC RIDGE...FROM THE CARIBBEAN THROUGH THE
CENTRAL/SOUTHERN FLORIDA PENINSULA...AND AREAS NEAR OR SOUTH AND
EAST OF THE MID ATLANTIC AND SOUTHERN NEW ENGLAND COAST.
ADDITIONALLY...GUIDANCE INDICATES MOISTENING WILL CONTINUE IN CLOSER
PROXIMITY TO THE LOW...PARTICULARLY ACROSS PARTS OF THE LOWER
MISSISSIPPI INTO LOWER OHIO VALLEYS...AIDED BY AN INFLUX OFF THE
WESTERN GULF OF MEXICO. ASSOCIATED DESTABILIZATION SHOULD AGAIN BE
SUFFICIENT FOR AREAS OF SCATTERED THUNDERSTORM ACTIVITY TODAY.
ISOLATED TO WIDELY SCATTERED THUNDERSTORM ACTIVITY WILL ALSO BE
POSSIBLE TODAY ACROSS PARTS OF THE WEST. THE MOST SUBSTANTIVE
CONCENTRATION IS EXPECTED TO REMAIN IN CONJUNCTION WITH A REMNANT
SHORT WAVE IMPULSE SLOWLY SHIFTING ACROSS THE SOUTHERN PLATEAU
TOWARD THE SOUTHERN ROCKIES.
...SERN PLAINS INTO UPPER PORTIONS OF THE LWR MS VALLEY...
CONVECTIVE DEVELOPMENT...INCLUDING THUNDERSTORM ACTIVITY...IS
ONGOING ACROSS PARTS OF SOUTHERN MISSOURI AND NORTHERN ARKANSAS...IN
ASSOCIATION WITH ONE SHORT WAVE IMPULSE PIVOTING AROUND THE CLOSED
LOW. IN ITS WAKE...AND AHEAD OF ANOTHER IMPULSE PIVOTING AROUND THE
WESTERN PERIPHERY OF THE LOW...ELEVATED MIXED LAYER AIR SHOULD
CONTINUE ADVECTING EAST OF THE SOUTHERN PLAINS TODAY. COUPLED WITH
THE LOW-LEVEL MOISTURE RETURN...WEAK TO MODERATE DESTABILIZATION
APPEARS PROBABLE ALONG AN AXIS ACROSS SOUTHERN/EASTERN ARKANSAS BY
THIS AFTERNOON...WITH MIXED LAYER CAPE INCREASING IN EXCESS OF 1000
J/KG. GUIDANCE SUGGESTS THAT THIS WILL OCCUR COINCIDENT WITH
STRENGTHENING FLOW FIELDS AND VERTICAL SHEAR...WHICH LIKELY WILL
BECOME SUFFICIENT FOR ORGANIZED CONVECTIVE DEVELOPMENT...INCLUDING
SUPERCELLS...AS LARGE-SCALE FORCING WEAKENS INHIBITION BY LATE
AFTERNOON. THE RISK FOR LARGE HAIL WILL ACCOMPANY THE STRONGEST
STORMS...WITH POTENTIAL FOR ONE OR TWO TORNADOES...AND PERHAPS AN
EVOLVING DAMAGING WIND THREAT...BEFORE CONVECTION WEAKENS AS IT
SPREADS EASTWARD INTO A MORE STABLE OR STABILIZING ENVIRONMENT EAST
OF THE LOWER MISSISSIPPI VALLEY THIS EVENING.
..KERR/DEAN.. 09/25/2011
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