SWODY1
SPC AC 210532
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1232 AM CDT SUN SEP 21 2008
VALID 211200Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE NRN PLAINS
AND CNTRL HIGH PLAINS...
...NRN PLAINS/CNTRL HIGH PLAINS...
A NEGATIVELY TILTED UPPER-LEVEL TROUGH IS FORECAST TO MOVE NEWD INTO
THE NRN PLAINS TODAY. AT THE SFC...A COLD FRONT WILL MOVE EWD ACROSS
ERN MT AND ERN WY. AHEAD OF THE FRONT...A STRONG LOW-LEVEL JET WILL
INCREASE MOISTURE NNWWD INTO THE SLIGHT RISK AREA WITH SFC DEWPOINTS
REACHING THE MID 50S F TO NEAR 60 F FROM ERN CO NWD INTO THE WRN
DAKOTAS. POCKETS OF MODERATE INSTABILITY SHOULD DEVELOP BY AFTERNOON
ALONG THE MOIST AXIS WHICH COMBINED WITH INCREASING LARGE-SCALE
ASCENT AHEAD OF THE UPPER-LEVEL TROUGH WILL BE FAVORABLE FOR
SCATTERED THUNDERSTORM DEVELOPMENT. SEVERAL STORM CLUSTERS SHOULD
PERSIST INTO THE EVENING AND MAY EVENTUALLY REACH THE ECNTRL DAKOTAS
BY THE OVERNIGHT PERIOD.
CONCERNING THE SEVERE POTENTIAL...VERTICAL SHEAR PROFILES ARE
FORECAST TO INCREASE THIS AFTERNOON ACROSS THE SLIGHT RISK AREA AS A
MID-LEVEL JET MOVES NEWD AROUND THE BASE OF THE TROUGH. FORECAST
SOUNDINGS AT 00Z MONDAY IN NE CO AND WRN NEB SHOW 0-6 KM SHEAR
VALUES OF 40 TO 50 KT WITH SOMEWHAT LESS VERTICAL SHEAR NWD INTO THE
WRN DAKOTAS. THE AMOUNT OF VERTICAL SHEAR COMBINED WITH STEEP
MID-LEVEL LAPSE RATES AND 500 MB TEMPS OF -12 TO -14C SHOULD BE
FAVORABLE FOR SUPERCELLS WITH LARGE HAIL. THE GREATEST SUPERCELL
POTENTIAL SHOULD BE IN THE CNTRL HIGH PLAINS WHERE VERTICAL SHEAR
WILL BE THE STRONGEST. A WIND DAMAGE THREAT WILL ALSO BE POSSIBLE
ESPECIALLY WITH MULTICELL LINE SEGMENTS WHEN LOW-LEVEL LAPSE RATES
ARE STEEP IN THE LATE AFTERNOON. THE WIND DAMAGE THREAT SHOULD
DECREASE BY MID-EVENING AS THE LOW-LEVEL JET STRENGTHENS AND
CONVECTION BECOMES ELEVATED.
..BROYLES/SMITH.. 09/21/2008
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