SWODY3
SPC AC 270718
DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0218 AM CDT SAT SEP 27 2008
VALID 291200Z - 301200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
THE INCREASINGLY AMPLIFIED UPPER FLOW PATTERN DEVELOPING LATE THIS
WEEKEND IS EXPECTED TO ENCOMPASS MUCH OF THE U.S. BY MONDAY. WITHIN
THIS REGIME...EAST OF A SHARP UPPER RIDGE OVER MUCH OF THE
INTERMOUNTAIN WEST/ROCKIES AND WESTERN CANADIAN PROVINCES...MODELS
INDICATE THAT A STRONG SHORT WAVE TROUGH WILL CONTINUE TO DIG
THROUGH THE GREAT LAKES AND MIDDLE MISSISSIPPI/OHIO VALLEY REGION.
HOWEVER...HIGH MOISTURE CONTENT AIR APPEARS LIKELY TO REMAIN
GENERALLY CONFINED TO THE FLORIDA PENINSULA...SOUTH/EAST OF BROAD
TROUGHING WITHIN A BRANCH OF WESTERLIES EXTENDING ACROSS THE MEXICAN
PLATEAU THROUGH THE GULF OF MEXICO AND LOWER LATITUDE WESTERN
ATLANTIC. AND...THE LACK OF A SIGNIFICANT SOUTHERLY RETURN FLOW OF
MOISTURE OFF THE GULF OF MEXICO IS EXPECTED TO CONTINUE TO LIMIT
CONVECTIVE POTENTIAL THROUGH THIS PERIOD.
...MIDDLE MISSISSIPPI/LOWER OHIO VALLEYS...
IN ADDITION TO THE MODEST AVAILABLE LOW-LEVEL MOISTURE...THE EROSION
OF THE ELEVATED MIXED LAYER TO THE LEE OF THE ROCKIES BY EARLY
MONDAY...IN CONJUNCTION WITH WEAK LOW-LEVEL FLOW AND LOW-LEVEL
FORCING FOR UPWARD VERTICAL MOTION...PROBABLY WILL MARGINALIZE THE
RISK FOR SEVERE STORMS MONDAY AFTERNOON AND EVENING.
HOWEVER...MODEL GUIDANCE DOES SUGGEST THAT AN AREA OF STRONGER
MID-LEVEL FORCING FOR UPWARD VERTICAL MOTION WITHIN 30-40+ KT
NORTHWESTERLY CYCLONIC MID-LEVEL FLOW WILL OVERSPREAD
ILLINOIS/MISSOURI DURING AND SHORTLY AFTER THE PEAK HEATING HOURS.
THIS IS EXPECTED TO CONTRIBUTE TO SUFFICIENT DESTABILIZATION FOR
SCATTERED THUNDERSTORM ACTIVITY...PERHAPS SOME OF WHICH COULD BE
CAPABLE OF PRODUCING HAIL/GUSTY SURFACE WINDS APPROACHING OR BRIEFLY
EXCEEDING SEVERE LIMITS.
..KERR.. 09/27/2008
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