SWODY1
SPC AC 070558
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1158 PM CST FRI MAR 06 2009
VALID 071200Z - 081200Z
...THERE IS A SLGT RISK OF SVR TSTMS TODAY/TONIGHT FROM PARTS OF THE
E CENTRAL PLAINS THRU THE MIDDLE MS VALLEY....
...SYNOPSIS...
MODELS INDICATE THAT A STRONG SHORT WAVE TROUGH...NOW DIGGING INTO
BRITISH COLUMBIA...WILL CONTINUE SOUTHEASTWARD TOWARD THE NORTHERN
INTERMOUNTAIN REGION DURING THIS FORECAST PERIOD. AS THIS
OCCURS...A SIGNIFICANT SHORT WAVE IMPULSE...WITHIN THE SOUTHERN
BRANCH OF DOWNSTREAM SPLIT POLAR WESTERLIES...IS PROGGED LIFT OUT OF
THE FOUR CORNERS STATES THROUGH THE CENTRAL PLAINS...WHILE A
NORTHERN STREAM SHORT WAVE TROUGH SHIFTS EAST SOUTHEAST OF ONTARIO
AND THE UPPER GREAT LAKES...TOWARD THE ST. LAWRENCE VALLEY. THIS
WILL ALL GRADUALLY CONTRIBUTE TO THE SUPPRESSION OF SUBTROPICAL
RIDGING CURRENTLY EXTENDING NORTHWARD THROUGH MUCH OF THE
SOUTHEASTERN QUARTER OF THE NATION.
HOWEVER...THE BULK OF THE CONVECTIVE DEVELOPMENT TODAY STILL APPEARS
LIKELY TO BE FOCUSED ALONG/NORTH OF A QUASI-STATIONARY FRONT ON THE
NORTHERN PERIPHERY OF THE UPPER RIDGE. THE RETURN FLOW OF MOISTURE
OFF THE WESTERN GULF OF MEXICO REMAINS RELATIVELY WEAK...BENEATH
WARM ELEVATED MIXED LAYER AIR EMANATING FROM THE PLATEAU REGION.
AND...MID-LEVEL CAPPING...COUPLED WITH CONSIDERABLE MID/HIGH-LEVEL
CLOUD COVER STREAMING NORTHEASTWARD OUT OF THE LOWER LATITUDE
PACIFIC...ALONG AND SOUTH OF THE SUBTROPICAL JET AXIS...IS EXPECTED
TO INHIBIT DESTABILIZATION AND DEEP CONVECTIVE DEVELOPMENT IN THE
WARM SECTOR.
...EAST CENTRAL PLAINS INTO THE OHIO VALLEY...
ONE OR MORE CLUSTERS OF STORMS WILL PROBABLY BE ONGOING AT
12Z...NEAR A LOWER/MID TROPOSPHERIC BAROCLINIC ZONE FROM PARTS OF
NORTHEAST KANSAS/SOUTHEAST NEBRASKA THROUGH SOUTHERN IOWA/NORTHERN
MISSOURI INTO PARTS OF NORTHWEST ILLINOIS. THIS IS WHERE LARGE-
SCALE ASCENT WILL BE ENHANCED BY FORCING IN THE RIGHT ENTRANCE
REGION OF A HIGH-LEVEL JET...WHICH IS PROGGED TO SHIFT EASTWARD
TOWARD THE NORTHEAST STATES DURING THE DAY. VARIABILITY EXISTS
AMONG THE GUIDANCE CONCERNING THE CONTINUING STRENGTH OF THIS
FORCING...BUT ELEVATED INSTABILITY MAY BE SUFFICIENT TO SUPPORT AT
LEAST LOW PROBABILITIES FOR HAIL IN THUNDERSTORM ACTIVITY SPREADING
ACROSS THE SOUTHERN/LOWER GREAT LAKES.
FARTHER WEST...THE MAIN UPPER IMPULSE IS NOT PROGGED TO SHIFT EAST
OF THE CENTRAL ROCKIES UNTIL LATE THIS EVENING OR OVERNIGHT.
HOWEVER...WEAKER SPEED MAXIMA EMBEDDED WITHIN THE PREVAILING STRONG
WEST SOUTHWESTERLY UPPER FLOW MAY CONTRIBUTE TO ADDITIONAL ROUNDS OF
STORMS...WITHIN A ZONE OF STEEP ISENTROPIC ASCENT ALONG THE STALLED
FRONT ACROSS NORTHEAST KANSAS/NORTHERN MISSOURI AND ADJACENT AREAS
OF NEBRASKA/IOWA. IN THE PRESENCE OF CONTINUING FAVORABLE
CONVECTIVE LAYER SHEAR AND COOL THERMODYNAMIC PROFILES WITH STEEP
MID-LEVEL LAPSE RATES...THE RISK FOR AT LEAST MARGINALLY SEVERE HAIL
WILL PERSIST.
IF BREAKS IN CLOUD COVER ALLOW FOR SUBSTANTIAL SURFACE HEATING... A
WINDOW OF OPPORTUNITY APPEARS TO EXIST FOR ISOLATED BOUNDARY LAYER
BASED STORM DEVELOPMENT NEAR THE SURFACE FRONT/DRY LINE INTERSECTION
ACROSS SOUTH CENTRAL/SOUTHEAST KANSAS LATE THIS AFTERNOON AND EARLY
EVENING. CLOCKWISE CURVED LOW-LEVEL HODOGRAPHS ACROSS THIS REGION
ARE EXPECTED TO BECOME SIZABLE...AS A SOUTHERLY 850 MB JET
STRENGTHENS...AND THE ENVIRONMENT SHOULD BECOME FAVORABLE FOR
CONSIDERABLE LOW/MID LEVEL UPDRAFT ROTATION WITHIN ANY STORMS THAT
DO FORM.
AS THE MAIN SURFACE LOW MIGRATES OUT OF THE TEXAS/OKLAHOMA PANHANDLE
AREA LATE THIS EVENING...AHEAD OF THE MAIN UPPER
IMPULSE...INCREASING STORM DEVELOPMENT APPEARS POSSIBLE ALONG AN
EASTWARD SURGING COLD FRONT ACROSS PARTS OF EASTERN
KANSAS/NORTHEASTERN OKLAHOMA INTO MISSOURI. ALTHOUGH THIS WILL
LIKELY BE AFTER THE COMMENCEMENT OF BOUNDARY LAYER STABILIZATION
...A FAVORABLY SHEARED ENVIRONMENT WITH STEEP MID-LEVEL LAPSE RATES
WILL SUPPORT A RISK FOR LARGE HAIL IN STRONGER STORMS...PERHAPS
LOCALIZED STRONG GUSTY WINDS.
..KERR/HURLBUT.. 03/07/2009
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