SWODY1
SPC AC 270523
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1123 PM CST WED NOV 26 2008
VALID 271200Z - 281200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
A LARGE COLD UPPER TROUGH/CLOSED LOW IS EXPECTED TO LINGER THROUGH
THIS FORECAST PERIOD ACROSS EASTERN CANADA AND THE NORTHEASTERN
STATES...WITHIN A NORTHERN BRANCH OF SPLIT POLAR WESTERLIES. AT THE
SAME TIME...TROUGHING IS PROGGED TO PERSIST WITHIN A SOUTHERN
BRANCH...ACROSS THE SOUTHWESTERN STATES. BUT...MODELS INDICATE THAT
A SIGNIFICANT IMPULSE WILL LIFT OUT OF THIS SOUTHERN STREAM
TROUGH...AS A VIGOROUS NORTHERN STREAM IMPULSE PROGRESSES INLAND
ACROSS THE PACIFIC NORTHWEST COAST...BEFORE DIGGING THROUGH THE
CANADIAN AND NORTHERN U.S. ROCKIES. THE SOUTHERN STREAM FEATURE
APPEARS LIKELY TO BECOME INCREASINGLY SHEARED AND WEAKEN AS IT
ACCELERATES INTO A CONFLUENT REGIME BETWEEN THE TWO BELTS OF
WESTERLIES...ACROSS THE SOUTH CENTRAL PLAINS. HOWEVER...SOME
SUPPRESSION OF SOUTHERN STREAM RIDGING MAY OCCUR ACROSS PARTS OF THE
SOUTHERN PLAINS INTO THE LOWER MISSISSIPPI VALLEY.
...SOUTHERN PLATEAU...
ONGOING INCREASING CONVECTIVE DEVELOPMENT ASSOCIATED WITH THE
SOUTHERN BRANCH IMPULSE MAY PERSIST INTO THE BEGINNING OF THE
FORECAST PERIOD ACROSS PARTS OF CENTRAL/SOUTHERN ARIZONA. HOWEVER
...LOW-LEVEL MOISTURE RETURN FROM THE GULF OF CALIFORNIA IS PROGGED
TO BECOME CUT-OFF DURING THE MORNING HOURS...AS LOW-LEVEL FLOW
VEERS. AND...COUPLED WITH REMNANT WIDESPREAD CLOUD COVER/
PRECIPITATION...THE POTENTIAL FOR SUBSTANTIAL DESTABILIZATION
THROUGH THE REMAINDER OF THE DAY PROBABLY SHOULD BE LIMITED...
DESPITE THE CONTINUING PRESENCE OF COLD AIR ALOFT. THUS...WHILE
SOME HAIL MAY ACCOMPANY STRONGER EARLY DAY STORMS...THIS RISK IS
EXPECTED TO DIMINISH DURING THE AFTERNOON HOURS...IF NOT BEFORE.
...WESTERN/CENTRAL GULF STATES...
CONSIDERABLE MOISTENING SUPPORTIVE OF CONVECTIVE POTENTIAL HAS
OCCURRED ACROSS THE WESTERN GULF OF MEXICO INTO PARTS OF SOUTHEAST
TEXAS. BUT...A GENERALLY WEAK AND WESTERLY COMPONENT TO THE
LOW-LEVEL FLOW FIELDS WILL ONLY RESULT IN A SLOW AND EASTWARD
ADVECTION OF THIS AIR MASS TOWARD CENTRAL GULF COASTAL AREAS AND
PARTS OF THE LOWER MISSISSIPPI VALLEY. CAPPING LAYERS BENEATH
MID/UPPER RIDGING ACROSS MUCH OF THIS REGION PROBABLY WILL SUPPRESS
DEEP CONVECTIVE DEVELOPMENT THROUGH MOST OF THE DAY...AS LARGE-SCALE
FORCING FOR UPWARD VERTICAL MOTION REMAINS WEAK. HOWEVER...GUIDANCE
CONTINUES TO SUGGEST THAT AN ISOLATED STORM OR TWO IS NOT OUT OF THE
QUESTION ACROSS PARTS OF SOUTHEAST TEXAS...WHERE INHIBITION FOR
MOIST BOUNDARY LAYER PARCELS CHARACTERIZED BY MID/UPPER 60S DEW
POINTS COULD BRIEFLY WEAKEN NEAR/SHORTLY AFTER PEAK HEATING. IF
THIS OCCURS...DEEP LAYER SHEAR BENEATH MODERATE TO STRONG MID/UPPER
FLOW WILL BE FAVORABLE FOR UPDRAFT ROTATION.
A SLIGHTLY BETTER CHANCE FOR THUNDERSTORM ACTIVITY MAY DEVELOP LATE
IN THE PERIOD...INTO EARLY FRIDAY...AS A SHALLOW COLD FRONT
ACCOMPANYING A NORTHERN STREAM IMPULSE ADVANCES SOUTHWARD INTO PARTS
OF CENTRAL/SOUTHEAST TEXAS AND THE LOWER MISSISSIPPI VALLEY.
STEEPER ISENTROPIC ASCENT ABOVE THIS FRONT...COUPLED WITH A GRADUAL
NORTH TO SOUTH COOLING ALOFT ACROSS THIS REGION...MAY BE SUFFICIENT
TO INITIATE SCATTERED STORMS...MOSTLY INLAND OF THE COASTAL PLAIN.
..KERR/HURLBUT.. 11/27/2008
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