SWODY1
SPC AC 080551
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1151 PM CST SAT MAR 07 2009
VALID 081200Z - 091200Z
...THERE IS A SLGT RISK OF SVR TSTMS TODAY...MAINLY FROM MID DAY
THROUGH EARLY EVENING...ACROSS PARTS OF THE MID MS AND LWR OH
VALLEYS....
...SYNOPSIS...
WHILE MODELS INDICATE THAT A PORTION OF THE LARGE COLD UPPER
TROUGH...NOW DIGGING ACROSS THE CANADIAN ROCKIES/PACIFIC
NORTHWEST...WILL SPLIT OFF INTO A NORTHERN BRANCH OF POLAR
WESTERLIES EXTENDING ACROSS CANADA...THE FIRST OF AT LEAST A COUPLE
OF IMPULSES IS PROGGED TO DIG INTO THE SOUTHERN STREAM...ACROSS THE
INTERMOUNTAIN WEST. AS THIS OCCURS...A SIGNIFICANT DOWNSTREAM
SOUTHERN BRANCH IMPULSE IS EXPECTED TO CONTINUE AN EASTWARD
ACCELERATION AROUND THE NORTHERN PERIPHERY OF PERSISTENT SUBTROPICAL
RIDGING ACROSS THE WESTERN ATLANTIC AND GULF OF MEXICO INTO THE
SOUTHEAST STATES. MID-LEVEL HEIGHT FALLS ASSOCIATED WITH THE
PERTURBATION SHOULD BRIEFLY SUPPRESS THE RIDGE ACROSS THE OHIO
VALLEY...BUT SHORT WAVE RIDGING IS EXPECTED TO RAPIDLY BUILD IN ITS
WAKE...ACROSS MUCH OF THE PLAINS/MISSISSIPPI VALLEY REGION LATE THIS
AFTERNOON AND TONIGHT.
IN RESPONSE TO THE EVOLVING UPPER PATTERN...A FAIRLY DEEP SURFACE
LOW APPEARS LIKELY TO MIGRATE FROM THE LOWER MISSISSIPPI VALLEY
THROUGH THE SOUTHERN GREAT LAKES REGION DURING THE DAY TODAY. THIS
WILL BE TRAILED BY A COLD FRONT...WHICH MAY ADVANCE SOUTHEASTWARD
THROUGH MUCH OF THE LOWER OHIO/TENNESSEE VALLEYS AND SOUTH CENTRAL
PLAINS...BEFORE STALLING AND WEAKENING. ALTHOUGH SURFACE DEW POINTS
WITHIN THE PRE-FRONTAL MOIST TONGUE MAY INCREASE FROM THE MID 50S TO
NEAR 60F AS FAR NORTH AS THE LOWER OHIO VALLEY...AND LOWER/MID
TROPOSPHERIC COOLING MAY WEAKEN INHIBITION...MID/UPPER HEIGHT RISES
ARE LIKELY TO SUPPRESS CONVECTIVE POTENTIAL FROM TEXAS
NORTHEASTWARD THROUGH AT LEAST MUCH OF THE LOWER MISSISSIPPI VALLEY.
...MIDDLE MISSISSIPPI INTO LOWER OHIO VALLEY...
EARLY DAY CLOUD COVER MAY SLOW DESTABILIZATION WITHIN THE WARM
SECTOR IN CLOSER PROXIMITY TO THE SURFACE LOW...FROM PARTS OF
EASTERN MISSOURI EASTWARD INTO THE LOWER OHIO VALLEY. BUT...BEFORE
MID-LEVEL SUBSIDENCE WITHIN AN EVOLVING DRY SLOT DIMINISHES
CONVECTIVE POTENTIAL...MODELS SUGGEST THAT A WINDOW OF OPPORTUNITY
WILL EXIST FOR VIGOROUS CONVECTIVE DEVELOPMENT ACROSS THE REGION.
THIS MAY COMMENCE BY 15-18Z...AS LOWER/MID TROPOSPHERIC COOLING
OVERTAKES A PRE-FRONTAL DRY LINE TYPE STRUCTURE EXPECTED FROM PARTS
OF CENTRAL ILLINOIS THROUGH EAST CENTRAL AND SOUTHEAST MISSOURI.
ALTHOUGH MIXED LAYER/MOST UNSTABLE CAPE MAY NOT MUCH EXCEED 500
J/KG...THIS SHOULD BE SUFFICIENT...GIVEN FAVORABLE LARGE-SCALE
FORCING...FOR A BROKEN LINE OF STORMS. THIS PROBABLY WILL INCLUDE A
FEW DISCRETE CELLS...IN THE PRESENCE OF STRONG DEEP LAYER SHEAR
FAVORABLE FOR SUPERCELLS...ACCOMPANIED BY THE RISK FOR LARGE HAIL
AND DAMAGING WINDS...WITH ISOLATED TORNADOES ALSO POSSIBLE. HIGHEST
PROBABILITIES APPEAR TO EXIST BENEATH STRONGEST DIFLUENCE
ALOFT...PROGGED TO SPREAD ACROSS PARTS OF CENTRAL/SOUTHERN ILLINOIS
AND INDIANA DURING THE 18-23Z TIME FRAME.
..KERR/HURLBUT.. 03/08/2009
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