SWODY1
SPC AC 141256
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0756 AM CDT MON JUL 14 2008
VALID 141300Z - 151200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON/EVENING FOR NRN
MN...
...NRN MN THIS AFTERNOON/EVENING...
THE LARGE SCALE FLOW IS EVOLVING TO A MORE ZONAL REGIME OVER THE NRN
TIER OF STATES AS THE MID LEVEL TROUGH OVER THE GREAT LAKES AND SE
CANADA FILLS AND LIFTS ENEWD. WITHIN THE ZONAL FLOW...A COUPLE OF
EMBEDDED SHORTWAVE TROUGHS WILL MOVE EWD/ESEWD FROM THE PRAIRIE
PROVINCES TO NEAR THE NRN BORDERS OF ND/MN. SEVERAL THUNDERSTORM
CLUSTERS ACCOMPANIED THE FIRST WAVE OVERNIGHT ACROSS SRN
SASKATCHEWAN...AND A SIMILAR OCCURRENCE APPEARS LIKELY THIS
AFTERNOON ACROSS NRN MN.
RESIDUAL BOUNDARY LAYER DEWPOINTS NOW IN THE 50S ACROSS CENTRAL/NW
MN WILL BE AUGMENTED SOME TODAY BY EVAPOTRANSPIRATION...WHILE
AFTERNOON TEMPERATURES OF 75-85 F WILL RESULT IN STEEP LOW-LEVEL
LAPSE RATES AND MINIMAL CONVECTIVE INHIBITION. THE REGION OF
SURFACE HEATING AND RESIDUAL MOISTURE WILL COINCIDE WITH A PLUME OF
STEEP MID LEVEL LAPSE RATES SPREADING EWD FROM THE NRN HIGH
PLAINS/ROCKIES...RESULTING IN AFTERNOON MLCAPE VALUES OF 500-1000
J/KG. EXPECT SCATTERED THUNDERSTORMS TO FORM ACROSS NRN MN BY MID
AFTERNOON ALONG A WEAK TROUGH/FRONTAL SURGE AND SPREAD ESEWD THROUGH
THE EVENING. THE STEEP LAPSE RATES AND COOL MID LEVEL TEMPERATURES
WILL BE CONDUCIVE TO HAIL FORMATION...AND THE HAIL THREAT WILL BE
AUGMENTED BY SUFFICIENT VERTICAL SHEAR FOR SUPERCELLS. THE STEEP
LOW-LEVEL LAPSE RATES MAY ALSO PROMOTE STRONG OUTFLOW WINDS.
...CENTRAL PLAINS AREA THIS EVENING...
LOW-LEVEL MOISTURE IS BEGINNING TO RETURN NWD FROM THE TX PANHANDLE
TOWARD WRN KS AND SW NEB. MODEL FORECASTS APPEAR TO BE TOO
AGGRESSIVE WITH FORECASTS OF MID-UPPER 60 DEWPOINTS IN NEB THIS
AFTERNOON...WITH ACTUAL VALUES LIKELY TO RANGE FROM THE LOW-MID 50S
ALONG THE LEE TROUGH IN WRN NEB...TO AROUND 60 F ACROSS NE NEB.
STILL...STRONG SURFACE HEATING AND STEEP MID LEVEL LAPSE RATES
SHOULD ALLOW THE DEVELOPMENT OF MLCAPE VALUES OF 1000-1500 J/KG THIS
AFTERNOON NEAR AND E OF THE LEE TROUGH IN NEB.
THE PRIMARY QUESTION FOR THIS AREA WILL BE THUNDERSTORM COVERAGE.
WEAK LOW-LEVEL LIFT ALONG THE SURFACE TROUGH AND SUFFICIENT MIXING
TO REDUCE CONVECTIVE INHIBITION ARE THE MAIN SUPPORTING FACTORS FOR
ISOLATED THUNDERSTORM DEVELOPMENT BEFORE DARK. STORM COVERAGE
SHOULD INCREASE SOME AFTER DARK AS A LLJ STRENGTHENS FROM KS INTO
NEB...AND A WEAK MID LEVEL TROUGH NOW OVER ID/NRN UT REACHES NEB.
THE STEEP LAPSE RATES AND EFFECTIVE BULK SHEAR OF 30-40 KT ALONG THE
SRN FRINGE OF THE STRONGER MID-UPPER FLOW COULD SUPPORT ISOLATED
SUPERCELLS WITH AN ACCOMPANYING THREAT FOR LARGE HAIL/DAMAGING
WINDS. IF CONFIDENCE IN STORM COVERAGE/INTENSITY INCREASES DURING
THE DAY...A SMALL SLIGHT RISK MAY NEED TO BE INTRODUCED ACROSS NEB
IN LATER UPDATES.
..THOMPSON/SMITH.. 07/14/2008
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