SPC AC 300549
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1249 AM CDT WED SEP 30 2009
VALID 301200Z - 011200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CNTRL
PLAINS...SRN PLAINS AND MID-MO VALLEY...
...CNTRL AND SRN PLAINS/MID-MO VALLEY/CNTRL ROCKIES...
AN IMPRESSIVE UPPER-LEVEL TROUGH OVER THE INTERMOUNTAIN WEST WILL
MOVE QUICKLY EWD INTO THE ROCKIES TODAY. THE SYSTEM WILL BECOME
NEGATIVELY-TILTED AS THE EXIT REGION OF A STRONG MID-LEVEL JET
BEGINS TO AFFECT THE CNTRL HIGH PLAINS LATE THIS AFTERNOON. VERY
STRONG LARGE-SCALE ASCENT...RAPID MOISTURE ADVECTION ASSOCIATED WITH
A POWERFUL 55-70 KT LOW-LEVEL JET AND MODERATE DESTABILIZATION WILL
LIKELY RESULT IN A SEVERE WEATHER EVENT THIS AFTERNOON THROUGH
TONIGHT FROM THE CNTRL HIGH PLAINS EWD INTO THE MID-MO VALLEY.
THE LATEST GPS-PRECIPITABLE WATER DATA SUGGESTS LOW-LEVEL MOISTURE
IS STARTING TO INCREASE ACROSS WEST TX INTO SW KS. AS HEIGHTS FALL
TODAY ACROSS THE REGION AHEAD OF THE APPROACHING TROUGH...MOISTURE
ADVECTION SHOULD MARKEDLY INCREASE AS A LOW-LEVEL JET BECOMES
ESTABLISHED ACROSS THE GREAT PLAINS. A DRYLINE WITH A RELATIVELY
NARROW AXIS OF MOISTURE IS FORECAST TO SET UP FROM THE ERN TX
PANHANDLE AND WRN OK NWD ACROSS WRN KS INTO WRN NEB BY LATE
AFTERNOON. MODEL FORECASTS ARE IN GOOD AGREEMENT DEVELOPING A POCKET
OF MODERATE INSTABILITY FROM DODGE CITY NWD TO NORTH PLATTE BY EARLY
THIS EVENING.
WELL WEST OF THE MOIST AXIS IN THE CNTRL ROCKIES...SCATTERED
THUNDERSTORMS WILL INITIATE THIS AFTERNOON IN THE STRONGLY DIFFLUENT
LEFT EXIT REGION OF THE MID-LEVEL JET. VERY STRONG VERTICAL SHEAR
AND SUBSTANTIAL LIFT SHOULD SUPPORT A MARGINAL THREAT FOR HAIL AND
STRONG WIND GUSTS IN WRN CO AND SRN WY. THE LEADING EDGE OF THIS
ACTIVITY SHOULD SPREAD EWD INTO SE WY AND NE CO BY 00Z WHERE MODEL
FORECASTS SHOW A NARROW INSTABILITY AXIS. IN SPITE OF SFC DEWPOINTS
ONLY IN THE 40S F IN NE CO...THE BROAD ZONE OF LIFT...STEEP LAPSE
RATES AND STRONG VERTICAL SHEAR EVIDENT ON FORECAST SOUNDINGS MAY BE
SUFFICIENT FOR ISOLATED ROTATING STORMS WITH HAIL. AS THIS CLUSTER
OF STORMS MOVES NEWD INTO THE CNTRL HIGH PLAINS DURING THE
EVENING...INTENSITY SHOULD INCREASE AS THE CONVECTION GAINS ACCESS
TO THE MOIST AXIS IN WRN NEB. FORECAST SOUNDINGS IN WRN NEB AT 06Z
SHOW SUBSTANTIAL VEERING WITH HEIGHT BELOW 850 MB WITH 40-50 KT OF
FLOW AROUND 500 MB AND 700-500 MB LAPSE RATES OF 8.0 TO 8.5 C/KM.
THIS SHOULD EASILY SUPPORT A SUPERCELL THREAT ACROSS WCNTRL NEB THIS
EVENING. DURING THE OVERNIGHT PERIOD...THE STORMS WILL BEGIN TO
INTERACT WITH THE LOW-LEVEL JET REACHING ERN NEB...WRN IA AND NE KS
LATE. THIS ACTIVITY SHOULD BE ELEVATED WITH HAIL BEING THE MAIN
THREAT.
SWD ALONG A DRYLINE THIS EVENING FROM NORTH PLATTE TO DODGE
CITY...FORECAST SOUNDINGS MAINTAIN STRONG VERTICAL SHEAR PROFILES
AND SHOW EVEN STEEPER MID-LEVEL LAPSE RATES SUGGESTING SOME
SUPERCELLS WITH VERY LARGE HAIL WILL BE POSSIBLE ESPECIALLY IF
MODERATE INSTABILITY IS REALIZED ALONG THIS CORRIDOR.
HOWEVER...CONVECTIVE COVERAGE SOUTH OF THE MID-LEVEL JET AXIS SHOULD
BE INCREASINGLY ISOLATED. IF A FEW STORMS CAN INITIATE FROM THE OK
PANHANDLE SWD ACROSS WEST TX THIS EVENING...LAPSE RATES APPEAR STEEP
ENOUGH AND VERTICAL SHEAR APPEARS STRONG ENOUGH FOR MARGINALLY
SEVERE HAIL AND STRONG WIND GUSTS.
..BROYLES/SMITH.. 09/30/2009
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
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