SWODY2
SPC AC 070620
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1220 AM CST SAT MAR 07 2009
VALID 081200Z - 091200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE MIDDLE
MISSISSIPPI/OHIO RIVER VALLEYS...
...SYNOPSIS...
MEAN LONGWAVE TROUGH WILL PERSIST OVER THE WESTERN HALF OF THE CONUS
ON SUNDAY. WHILE A BROAD TROUGH DIGS SOUTHEASTWARD ACROSS THE
PACIFIC NORTHWEST/NORTHERN INTERMOUNTAIN REGION...A RELATIVELY
COMPACT/NEGATIVELY TILTED SHORTWAVE TROUGH AND ASSOCIATED 70 KT MID
LEVEL JET STREAK ARE FORECAST TO SPREAD NORTHEASTWARD ACROSS THE
UPPER MISSISSIPPI VALLEY/UPPER GREAT LAKES VICINITY. THIS SYSTEM
ACROSS THE MIDWEST...AND ITS ADVANCING SURFACE LOW/COLD FRONT...WILL
SERVE AS THE PRIMARY FOCUS FOR DEEP CONVECTIVE/SEVERE TSTM POTENTIAL
ON SUNDAY.
...MIDDLE MISSISSIPPI/OHIO RIVER VALLEYS...
WITH THE AFOREMENTIONED SHORTWAVE TROUGH LIKELY TO BE REACHING THE
MIDDLE MISSOURI VALLEY AT THE BEGINNING OF THE PERIOD...SCATTERED
TSTMS WILL BE ONGOING SUNDAY MORNING ACROSS THE MIDWEST/MIDDLE
MISSISSIPPI VALLEY WITHIN AN ELEVATED MOISTURE TRANSPORT REGIME
AIDED BY A 50+ KT LOW LEVEL JET. STRONG SHEAR THROUGH THE CLOUD
BEARING LAYER AND 500-1000 J/KG OF ELEVATED MUCAPE SUGGESTS THESE
EARLY DAY TSTMS MAY CONTINUE TO POSE MAINLY A HAIL THREAT DURING THE
MORNING ACROSS PORTIONS OF MO/IL/EASTERN IA AND PERHAPS NORTHERN
INDIANA.
WITH TIME...GRADUAL DIURNAL DESTABILIZATION AND A SOUTHWESTERLY
MOISTURE INFLUX OF UPPER 50S/NEAR 60F SURFACE DEWPOINTS SHOULD LEAD
TO AN UPSWING IN TSTM INTENSITY BY EARLY AFTERNOON AHEAD OF THE
ADVANCING SURFACE LOW/COLD FRONT. THIS SHOULD INITIALLY OCCUR ACROSS
FAR EAST CENTRAL/SOUTHEAST MO AND THE DOWNSTATE PORTIONS OF IL INTO
INDIANA. TOTAL BUOYANCY IN THE PREFRONTAL WARM SECTOR WILL NOT BE
PARTICULARLY ROBUST...BUT SUFFICIENT INSOLATION/UNSEASONABLY WARM
TEMPERATURES BENEATH RELATIVELY STEEP MID LEVEL LAPSE RATES SHOULD
SUPPORT MLCAPES AS HIGH AS 750-1000 J/KG. STRONG 60-75 KT MID LEVEL
FLOW/MODEST VEERING WOULD SUPPORT BOTH SUPERCELLS AND THE
DEVELOPMENT OF FAST MOVING BOWS. DAMAGING WINDS AND SEVERE HAIL
SHOULD BE THE PRIMARY RISKS...ALTHOUGH MODEST VEERING/50 KT FLOW
AROUND 1 KM SUGGESTS A BRIEF TORNADO OR TWO CANNOT BE RULED OUT.
...ARKLATEX VICINITY...
FARTHER SOUTHWEST...THE SEVERE THREAT APPEARS MUCH MORE
ISOLATED/CONDITIONAL ACROSS THE ARKLATEX VICINITY ON SUNDAY. THIS IS
ATTRIBUTABLE TO WEAKER/AMORPHOUS LARGE SCALE FORCING IN THE WAKE OF
THE MIDWEST UPPER TROUGH AND WEAKENING FRONTAL CONVERGENCE ALONG THE
STALLING COLD FRONT. NEVERTHELESS...STRONG WIND FIELDS ALOFT ATOP
AROUND 60/PERHAPS LOWER 60S F SURFACE DEWPOINTS WOULD CONDITIONALLY
SUPPORT A SEVERE RISK WITH HAIL AS THE PRIMARY THREAT. WILL MAINTAIN
5% SEVERE PROBABILITIES AT THIS TIME AS A PARTICULARLY
ORGANIZED/WIDESPREAD SEVERE RISK IS NOT CURRENTLY EXPECTED.
...PACIFIC NORTHWEST/NORTHERN INTERMOUNTAIN WEST...
A FEW TSTMS WILL BE POSSIBLE ACROSS THE COASTAL PACIFIC
NORTHWEST...AND PERHAPS THE INTERIOR INTERMOUNTAIN WEST...AS A COLD
UPPER TROUGH ADVANCES EAST-SOUTHEASTWARD ACROSS THE REGION.
SPORADIC/LOW PROBABILITY POTENTIAL DOES NOT WARRANT A TSTM OUTLOOK
AT THIS TIME.
..GUYER.. 03/07/2009
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