SPC AC 011623
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1123 AM CDT THU MAY 01 2008
VALID 011630Z - 021200Z
...THERE IS A MDT RISK OF SVR TSTMS OVER SERN KS...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE
SRN/CENTRAL PLAINS...
...SYNOPSIS...
STRONG SPRING UPPER SYSTEM WILL SPREAD EWD ACROSS THE HIGH PLAINS
THROUGH THE PERIOD...WITH ASSOCIATED ENHANCED MID/UPPER LEVEL WIND
FIELDS SPREADING ACROSS MUCH OF THE CENTRAL PLAINS. MID MORNING
SURFACE ANALYSES INDICATE SURFACE LOW OVER CENTRAL NEB WHICH WILL
DEEPEN SOME AS IT LIFTS SLOWLY NWD THROUGH THE DAY. AS THIS
OCCURS...DEEP MIXING WITHIN DRY TROPOSPHERE AND DOWNWARD MIXING OF
STRONG SWLY FLOW ALOFT WILL ALLOW DRYLINE TO DEVELOP EWD ACROSS A
LARGE PART OF SERN NEB/NERN KS...TRAILING SSWWD INTO CENTRAL OK BY
LATE THIS AFTERNOON. MAIN NEGATIVE FACTOR FOR WIDESPREAD AND/OR
SIGNIFICANT SEVERE THUNDERSTORMS ACROSS A LARGE AREA REMAINS THE
LIMITED MOISTURE AND STRONG CAPPING. MOISTURE RETURN HAS NOT BEEN
HELPED THUS FAR BY STRONG SWLY LLJ EXTENDING FROM ERN TX ACROSS THE
MID MS RIVER VALLEY. HOWEVER...SECONDARY SLY LLJ IS FORECAST TO
DEVELOP LATE IN THE DAY/OVERNIGHT OVER ERN OK IN RESPONSE TO MAIN
ENERGY EJECTING EWD ACROSS THE PLAINS LATE IN THE PERIOD.
REGARDLESS...INTENSE SYSTEM AND ASSOCIATED LARGE SCALE ASCENT WILL
INCREASE SEVERE THUNDERSTORM THREAT THROUGH THE LATTER HALF OF THE
PERIOD AS STRONG SURFACE COLD FRONT OVERTAKES DRY LINE. PRIOR TO
THIS OCCURRING THIS EVENING...12Z GFS AND NAM BOTH FAVOR BACKING
WINDS WITHIN THE WARM SECTOR OVER ERN OK/SERN KS AND A SLIGHT NWWD
SHIFT TO THE DRY LINE INTO MORE OF S-CENTRAL KS/N-CENTRAL OK BETWEEN
00-03Z AS SURFACE LOW DEVELOPS IN RESPONSE TO APPROACH OF MAIN
IMPULSE.
...LOWER MO RIVER VALLEY INTO OK/WRN AR/WRN MO...
DIURNAL DEVELOPMENT ALONG DRY LINE WILL REMAIN CONDITIONAL DUE TO
FACTORS LISTED ABOVE. HOWEVER...STRONG HEATING AND CONTINUED INFLUX
OF LOWER 60S SURFACE DEW POINTS WILL LIKELY GREATLY WEAKEN CAP FROM
FAR NERN KS ACROSS SERN KS/FAR NRN OK THIS AFTERNOON. SHOULD EVEN
ONE OR TWO STORMS FIRE DURING THE AFTERNOON/EARLY EVENING ACROSS
THIS REGION...THEY COULD EASILY EVOLVE INTO LONG-LIVED SUPERCELLS
GIVEN MLCAPE AOA 2500 J/KG AND 40-50 KT DEEP LAYER SHEAR. COVERAGE
OF STORMS WILL INCREASE THROUGH THE EVENING...WHICH WILL ALSO EVOLVE
AS SUPERCELLS AND LINES/BOW ECHOES AS FRONT OVERCOMES CAPPING. THIS
ACTIVITY WILL EXPAND SWD AS STORMS SHIFT GENERALLY EWD ACROSS ERN
KS/ERN OK/WRN MO/WRN AR THROUGH THE NIGHT. VERY STEEP LAPSE RATES
WILL FAVOR LARGE HAIL AND DAMAGING WINDS...ALTHOUGH TORNADOES CAN
NOT BE RULED OUT WITH THE OVERNIGHT STORMS GIVEN VERY STRONG LOWER
AND DEEP LAYER SHEAR IN PLACE.
...MID MO RIVER VALLEY...
STRONG SURFACE PRESSURE FALLS WILL SPREAD NWD TOWARDS FAR SERN
SD/NERN NEB THROUGH THE DAY AHEAD OF APPROACHING LOW CENTER. DEEP
ASCENT AND WEAKENING CAP AS AFTERNOON TEMPERATURES RISE INTO THE 70S
SHOULD SUPPORT THUNDERSTORMS WITHIN WARM SECTOR OVER THIS REGION.
LOW LEVEL SHEAR WILL BE ENHANCED FROM ESELY SURFACE WINDS AND EXPECT
A FEW SUPERCELLS WILL DEVELOP WITH THREATS OF LARGE HAIL AND
ISOLATED TORNADOES INTO THE EARLY EVENING. STORMS SHOULD EVOLVE
ALONG THE FRONT AND MAINTAIN A RISK OF SEVERE EWD ACROSS FAR ERN NEB
AND INTO WRN IA DURING THE EVENING PRIOR TO STORMS SHIFTING EAST OF
GREATER INSTABILITY AXIS.
..EVANS/GRAMS.. 05/01/2008
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