SWODY1
SPC AC 290547
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1147 PM CST SAT NOV 28 2009
VALID 291200Z - 301200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
WITHIN A STRONGER BELT OF WESTERLIES ACROSS THE NORTHERN TIER
STATES...MODELS INDICATE THAT A TROUGH WILL AMPLIFY SOUTHEASTWARD
FROM THE UPPER MISSISSIPPI VALLEY THROUGH THE GREAT LAKES/OHIO
VALLEY DURING THIS FORECAST PERIOD. THIS IS PROGGED TO FLATTEN
BROADER SCALE RIDGING DOWNSTREAM OF THE CLOSED LOW NOW DIGGING
THROUGH THE SOUTHWESTERN STATES...CONTRIBUTING TO INTENSIFYING WEST
SOUTHWESTERLY MID/UPPER FLOW ACROSS THE MID SOUTH INTO THE UPPER
OHIO VALLEY. MEANWHILE...GUIDANCE SUGGESTS THAT THE CLOSED LOW WILL
CONTINUE TO SLOWLY DIG SOUTHWARD THROUGH THE NORTHERN GULF OF
CALIFORNIA VICINITY...WHILE BROAD RIDGING IN THE NORTHERN STREAM
SHIFTS EASTWARD NEAR THE WESTERN CANADIAN/U.S. BORDER.
...SOUTHWESTERN STATES...
INSTABILITY BENEATH THE MID-LEVEL COLD POOL ASSOCIATED WITH THE
CLOSED LOW...COUPLED WITH DIFLUENT AND DIVERGENT UPPER FLOW...ARE
EXPECTED TO CONTRIBUTE TO AFTERNOON/EARLY EVENING THUNDERSTORM
ACTIVITY ACROSS THE NORTHWESTERN MEXICAN PLATEAU INTO THE HIGHER
TERRAIN OF EASTERN ARIZONA AND WESTERN NEW MEXICO.
...SOUTHEAST TEXAS INTO PARTS OF THE OH/TN VALLEYS...
THE BOUNDARY LAYER OVER THE GULF OF MEXICO IS STILL IN THE PROCESS
OF MODIFYING IN THE WAKE OF PRIOR COLD INTRUSIONS...BUT A WEAK TO
MODEST RETURN FLOW OF MOISTURE IS ALREADY UNDERWAY ACROSS SOUTHEAST
TEXAS THROUGH THE ARKLATEX AND PARTS OF THE OZARK PLATEAU. THE
EVOLVING UPPER PATTERN SHOULD MAINTAIN THIS THROUGH THIS
PERIOD...AHEAD OF A COLD FRONT ADVANCING EAST OF THE MISSISSIPPI
VALLEY AND SOUTHWARD TOWARD THE WESTERN GULF COAST...IN ASSOCIATION
WITH THE NORTHERN BRANCH TROUGH. AS THIS OCCURS...STRENGTHENING
FRONTOGENETIC FORCING MAY ENHANCE BROADER SCALE FORCING FOR UPWARD
VERTICAL MOTION OVERSPREADING THE REGION LATE IN THE AFTERNOON
THROUGH THE EVENING HOURS. DESTABILIZATION IS EXPECTED TO BE
SUPPORTIVE OF AN EVOLVING CONVECTIVE BAND WITH EMBEDDED
THUNDERSTORMS. SOME OF THIS ACTIVITY MAY INITIATE WITHIN A WEAKLY
UNSTABLE BOUNDARY LAYER CHARACTERIZED BY CAPE ON THE ORDER OF 500
J/KG...INLAND OF THE UPPER TEXAS COASTAL PLAIN THROUGH THE ARKLATEX.
HOWEVER...IN THE PRESENCE OF WEAK MID-LEVEL LAPSE RATES AND WEAK
LOW-LEVEL FLOW FIELDS/SHEAR...SEVERE POTENTIAL FOR TODAY STILL SEEMS
NEGLIGIBLE.
..KERR/SMITH.. 11/29/2009
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