SWODY1
SPC AC 201954
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0254 PM CDT FRI APR 20 2007
VALID 202000Z - 211200Z
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE NRN AND
CNTRL HIGH PLAINS...
..NRN PLAINS...
LATEST WATER VAPOR IMAGERY AND RUC ANALYSIS SHOW A SUBTLE SHORTWAVE
TROUGH MOVING NEWD ACROSS ERN CO AND THE CNTRL PLAINS ATTM. AS THIS
SYSTEM APPROACHES THE NRN PLAINS LATE THIS AFTERNOON...LARGE-SCALE
ASCENT WILL BECOME INCREASINGLY FAVORABLE FOR THUNDERSTORM
DEVELOPMENT ACROSS THE REGION INTO THE EVENING. IN
ADDITION...STRENGTHENING LOW-LEVEL FLOW AND INCREASING LOW-LEVEL
MOISTURE WILL BECOME MORE FAVORABLE WITH TIME.
OBJECTIVE ANALYSIS AND REGIONAL PROFILERS ACROSS THE NRN PLAINS
CURRENTLY SHOW 0-6 KM SHEAR VALUES IN THE 40 TO 55 KT RANGE. THIS
AMOUNT OF VERTICAL SHEAR WILL BE MARGINALLY SUFFICIENT FOR ROTATING
STORMS DUE TO THE WEAKER INSTABILITY IN PLACE. THE GREATEST
SUPERCELL THREAT SHOULD REMAIN FURTHER SOUTH SOUTHWEST WHERE
MODERATE INSTABILITY IS EXPECTED. THUNDERSTORM COVERAGE WILL
CONTINUE TO BE GREATEST ACROSS ECNTRL AND NERN SD WITH STORMS
GRADUALLY EXPANDING NWD INTO CNTRL AND ERN ND. FORECAST SOUNDINGS
THIS EVENING ACROSS MOST OF THE NRN PLAINS SHOW STEEP LAPSE
RATES...COLD TEMPS ALOFT /500 MB TEMPS < -16 C/ WHICH COMBINED WITH
THE STRONG VERTICAL SHEAR WILL BE ENOUGH FOR ISOLATED LARGE HAIL
WITH THE MORE ORGANIZED THUNDERSTORMS. CONSIDERING THE INSTABILITY
IS MOSTLY LOCATED ABOVE 700 MB...THUNDERSTORMS SHOULD REMAIN
PRIMARILY ELEVATED IN THE NRN PLAINS AND THE THREAT FOR WIND DAMAGE
SHOULD REMAIN MARGINAL.
..WRN NEB/WRN KS AND THE TX PANHANDLE...
LATEST SFC ANALYSIS SHOWS A MOIST AXIS EXTENDING NWD FROM WCNTRL OK
INTO CNTRL KS WITH SFC DEWPOINTS IN THE LOWER 60S F. ACCORDING TO
OBJECTIVE ANALYSIS...MODERATE INSTABILITY IS CURRENTLY PRESENT ALONG
THE MOIST AXIS AND SHORT-TERM MODEL FORECASTS MOVE THE INSTABILITY
WWD INTO THE CNTRL HIGH PLAINS THIS EVENING. A CAPPING INVERSION IS
PRESENT ALONG THE INSTABILITY AXIS AND THIS WILL INHIBIT CONVECTIVE
DEVELOPMENT THROUGH MOST OF THE AFTERNOON. ISOLATED CONVECTIVE
DEVELOPMENT MAY OCCUR IN A NARROW WINDOW LATE THIS AFTERNOON OR
EARLY THIS EVENING AS THE CAPPING INVERSION BECOMES WEAKER ACROSS
THE REGION. THE GREATEST POTENTIAL FOR THUNDERSTORMS WILL EXIST
ACROSS WRN NEB WHERE LARGE-SCALE ASCENT ASSOCIATED WITH A SHORTWAVE
TROUGH WILL BE MORE FAVORABLE.
FORECAST SOUNDINGS AND OBJECTIVE ANALYSIS ACROSS THE REGION EARLY
THIS EVENING SHOW MODERATE VERTICAL SHEAR IN PLACE WITH 0-6 KM SHEAR
VALUES IN THE 35 TO 45 KT RANGE. CONSIDERING MODERATE INSTABILITY IS
ALREADY PRESENT...SUPERCELLS WILL BE LIKELY WITH STORMS THAT
INITIATE. IN ADDITION...MID-LEVEL LAPSE RATES MAY INCREASE AS AN
ELEVATED MIXED LAYER OVER SE CO DRIFTS NEWD THIS EVENING. THIS ALONG
WITH THE INCREASING INSTABILITY AND ADEQUATE SHEAR WILL BE FAVORABLE
FOR LARGE HAIL WITH ANY SUPERCELL. IF A SUPERCELL OR TWO
DEVELOP...VERY LARGE HAIL AND ISOLATED WIND DAMAGE WILL ALSO BE
POSSIBLE.
.BROYLES.. 04/20/2007
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