DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 211241
SWODY1
SPC AC 211239

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0739 AM CDT FRI SEP 21 2012

VALID 211300Z - 221200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
THE HIGH AMPLITUDE LARGE SCALE FLOW OVER NORTH AMERICA IS COMPOSED
OF A WESTERN/ROCKIES UPPER RIDGE AND A DOWNSTREAM DEEP TROUGH
EXTENDING FROM HUDSON BAY SOUTH ACROSS THE GREAT LAKES. GIVEN THE
BLOCKING NATURE OF THE FLOW ONLY A SMALL EWD SHIFT IN THE PATTERN IS
EXPECTED THIS PERIOD. A TROUGH WILL EDGE CLOSER TO THE PACIFIC
NORTHWEST FROM OFFSHORE AND A NUMBER OF SMALLER SCALE PERTURBATIONS
WILL ROTATE THROUGH THE BASE OF THE LARGER UPPER TROUGH ACROSS THE
UPPER MS VALLEY...GREAT LAKES AND MIDWEST.

...MIDWEST...
MORNING PROFILER AND VWP DATA DEPICT A WSWLY LOW LEVEL JET DIRECTED
ACROSS A WEAK RESIDUAL FRONTAL ZONE FROM NERN OK TO THE CONFLUENCE
OF THE OH/MS RIVERS. ISENTROPIC LIFT AND MOISTENING WITHIN THIS ZONE
CONTRIBUTED TO ELEVATED TSTM INITIATION SHORTLY AFTER MIDNIGHT OVER
SRN MO. THIS CONVECTION HAS SPREAD ESEWD ACROSS NERN AR AND IS
FORECAST TO SLOWLY DISSIPATE WHILE MOVING EAST OF THE MS RIVER LATER
TODAY.

IN THE WAKE OF THE MORNING STORMS...A CLIPPER-LIKE LOW PRESSURE
SYSTEM WILL TRACK ACROSS THE IA/MO BORDER THIS AFTERNOON AND INTO
WRN IL THIS EVENING. MOISTURE TRANSPORT INTO/AHEAD OF THIS NEXT
DISTURBANCE WILL BE LIMITED. NONETHELESS...IT SEEMS PROBABLE THAT A
NARROW PLUME OF MID-UPPER 50S F SFC DEWPOINTS WILL BE SITUATED FROM
ERN MO INTO WRN IL BY LATE AFTERNOON/EARLY EVENING...COINCIDENT WITH
THE DEEPENING LOW PRESSURE. BOUNDARY LAYER WARMING WITHIN THIS
CORRIDOR...IN COMBINATION WITH AN AXIS OF STEEPER LAPSE RATES
ALOFT...SHOULD ALLOW FOR MLCAPE TO REACH 300-800 J/KG WITHIN THE
COMPACT WARM SECTOR AHEAD OF AND NEAR THE SFC LOW. THESE MLCAPE
ESTIMATES ARE LOWER THAN INDICATED IN LATEST NAM AND GFS GUIDANCE
AND CLOSER TO LATEST HRRR AND SREF GUIDANCE.

MASS ADJUSTMENTS IN THE EXIT REGION OF A MID/UPPER JET NOSING OVER
THE REGION FROM THE CNTRL/NRN PLAINS WILL ACT TO FOCUS ASCENT AND
WARM ADVECTION NEAR AND EAST OF THE SFC LOW WHERE STORM INITIATION
SEEMS MOST LIKELY. STRENGTHENING MID LEVEL WLY FLOW OF 50-60KT WILL
RESULT IN ADEQUATE SHEAR PERSISTING/ROTATING UPDRAFTS AND STORMS
CAPABLE OF BOTH WIND AND HAIL. SOME FORECAST HODOGRAPHS NEAR THE SFC
LOW OVER IL EXHIBIT MODEST SRH VALUES SUPPORTIVE OF SOME WEAK/BRIEF
TORNADO POTENTIAL. AT THIS TIME...ANYTHING MORE THAN VERY ISOLATED
SEVERE WEATHER FROM THE DEVELOPING CONVECTION WILL REMAIN
CONDITIONAL ON GREATER DESTABILIZATION OCCURRING THAN IS CURRENTLY
ANTICIPATED. HIGHER PROBABILITIES MAY BE NEEDED IN LATER OUTLOOKS IF
GREATER LOW LEVEL MOISTURE MATERIALIZES AND ACTS TO BOOST MLCAPE
VALUES.

..CARBIN/BOTHWELL.. 09/21/2012

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