SWODY1
SPC AC 180522
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1222 AM CDT THU SEP 18 2008
VALID 181200Z - 191200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
MODELS INDICATE THAT THE UPPER PATTERN WILL REMAIN MOSTLY ZONAL
THROUGH THIS PERIOD...WITH THE STRONGER FLOW ASSOCIATED WITH THE
MAIN POLAR JET LINGERING AT THE HIGHER LATITUDES...GENERALLY NORTH
OF THE CANADIAN/U.S. BORDER. A SERIES OF IMPULSES ARE FORECAST TO
PROGRESS THROUGH A BELT SPLITTING OFF THIS STREAM...ACROSS THE
EASTERN PACIFIC THROUGH THE CENTRAL/SOUTHERN TIER STATES. BUT...
THESE FEATURES ARE EXPECTED TO REMAIN OUT OF PHASE WITH THE
SUBTROPICAL STREAM...EXTENDING IN A WESTERLY BELT ACROSS BAJA AND
THE NORTHERN MEXICAN PLATEAU INTO THE CARIBBEAN.
WHILE SIGNIFICANT SURFACE CYCLOGENESIS APPEARS LIKELY TO ACCOMPANY
ONE POLAR SHORT WAVE ACROSS THE CENTRAL CANADIAN PROVINCES...LOW-
LEVEL RIDGING IS EXPECTED TO BE PROMINENT ACROSS MUCH OF THE SOUTH
CENTRAL STATES INTO THE ATLANTIC SEABOARD. THIS SHOULD PRECLUDE THE
DEVELOPMENT OF A RETURN FLOW OF MOISTURE OFF THE GULF OF
MEXICO...MAINTAINING LOW CONVECTIVE POTENTIAL ACROSS MUCH OF THE
NATION.
...PACIFIC STATES INTO THE ROCKIES...
IN THE WAKE OF AN UPPER TROUGH SHIFTING EASTWARD THROUGH THE
CENTRAL/SOUTHERN PLAINS...AND AHEAD OF ANOTHER CLOSED LOW/TROUGH
APPROACHING CENTRAL PACIFIC COASTAL AREAS...MOISTURE LEVELS ARE NOT
EXPECTED TO BE PARTICULARLY HIGH EVEN ACROSS MUCH OF THE WEST. AN
EXCEPTION MAY BE ACROSS THE SOUTHERN CALIFORNIA DESERTS AND PARTS OF
THE LOWER COLORADO VALLEY...WHERE LINGERING MOISTURE MAY AGAIN BE
SUPPORTIVE OF MODERATE TO STRONG POTENTIAL INSTABILITY WITH STRONG
DAYTIME HEATING. FORECAST SOUNDINGS ACROSS THIS REGION INDICATE
THAT A MID-LEVEL SUBSIDENCE INVERSION COULD BE INHIBITIVE OF
CONVECTIVE DEVELOPMENT. BUT...FAVORABLE OROGRAPHY AND INCREASINGLY
DIFLUENT/DIVERGENT UPPER FLOW ARE EXPECTED TO PROVIDE SUPPORT FOR AT
LEAST WIDELY SCATTERED LATE AFTERNOON STORMS.
ADDITIONAL SCATTERED STORMS APPEAR POSSIBLE ACROSS THE HIGHER
TERRAIN OF THE FOUR CORNERS STATES. BUT...HIGHEST PROBABILITIES
MAY EXIST ACROSS THE MOUNTAINS OF WESTERN/CENTRAL COLORADO INTO
NORTH CENTRAL/NORTHEAST NEW MEXICO. THIS IS WHERE MODELS SUGGEST
THAT FORCING ASSOCIATED WITH AN UPPER SPEED MAXIMUM DIGGING INTO THE
LARGER SCALE TROUGH ACROSS PLAINS MAY ENHANCE UPWARD VERTICAL MOTION
THIS AFTERNOON AND EVENING.
...NORTHERN PLAINS INTO NORTHERN MINNESOTA...
MOISTURE NEAR A LOW-LEVEL THERMAL RIDGE/SURFACE TROUGH EXTENDING
SOUTHWEST OF THE DEVELOPING CENTRAL CANADIAN SURFACE CYCLONE MAY BE
SUFFICIENT FOR WEAK DESTABILIZATION THIS AFTERNOON. AND... ISOLATED
TO WIDELY SCATTERED HIGH-BASED CONVECTION APPEARS POSSIBLE.
RELATIVELY LOW PROBABILITIES FOR THUNDERSTORMS COULD INCREASE A BIT
THIS EVENING...ASSOCIATED WITH FORCING NEAR A STRENGTHENING
SOUTHERLY LOW-LEVEL JET AXIS.
...FLORIDA...
EASTERLY LOW-LEVEL FLOW WILL MAINTAIN A MOIST ENVIRONMENT ACROSS THE
PENINSULA...WITH SUFFICIENT DESTABILIZATION EXPECTED DURING THE DAY
TO SUPPORT AT LEAST SCATTERED AFTERNOON THUNDERSTORMS.
..KERR.. 09/18/2008
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