SWODY1
SPC AC 211956
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0256 PM CDT SAT APR 21 2007
VALID 212000Z - 221200Z
..THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF WEST TX...NW
OK...WRN KS AND WRN NEB...
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS THE SRN
PLAINS...CNTRL HIGH PLAINS AND NRN PLAINS...
..SRN AND CNTRL HIGH PLAINS...
LATEST WATER VAPOR IMAGERY SHOWS AN UPPER-LEVEL LOW AND TROUGH OVER
THE FOUR CORNERS REGION. A WELL-FOCUSED 85 KT MID-LEVEL JET IS
LOCATED ACROSS FAR SRN NM AND THIS FEATURE WILL BEGIN TO AFFECT WEST
TX OVER THE NEXT FEW HOURS. STRONG ASCENT ASSOCIATED WITH THE
UPPER-LEVEL TROUGH AND EXIT REGION OF THE MID-LEVEL JET SHOULD
PROMOTE RAPID THUNDERSTORM DEVELOPMENT THIS AFTERNOON. AS A CAPPING
INVERSION WEAKENS ACROSS THE REGION...NUMEROUS THUNDERSTORMS WILL
LIKELY DEVELOP ALONG THE WRN EDGE OF THE MOIST AXIS FROM NEAR THE
CO/KS STATE-LINE EXTENDING SWD TO NEAR AMARILLO AND JUST WEST OF
LUBBOCK TX. THUNDERSTORMS SHOULD RAPIDLY INCREASE EARLY THIS
EVENING MOVING EWD ACROSS THE MODERATE RISK AREA.
FORECAST SOUNDINGS AND OBJECTIVE ANALYSIS ACROSS THE MODERATE RISK
AREA CURRENTLY SHOW 0-6 KM SHEAR VALUES AROUND 40 KT AND VERTICAL
SHEAR SHOULD CONTINUE TO INCREASE AS THE MID-LEVEL JET EJECTS NEWD
ACROSS THE REGION. AS A RESULT...WIND FIELDS WILL BE QUITE FAVORABLE
FOR SUPERCELLS AND BOW ECHOES. TORNADOES WILL BE POSSIBLE WITH
SUPERCELLS THAT INITIATE AND WITH THE STRONGER BOW ECHOES. IF A
SIGNIFICANT TORNADO THREAT DEVELOPS...THE MOST LIKELY AREA WOULD BE
IN THE ECNTRL TX PANHANDLE WHERE LOW-LEVEL SHEAR PROFILES APPEAR
MOST FAVORABLE. IN ADDITION...STEEP MID-LEVEL LAPSE RATES...STRONG
VERTICAL SHEAR AND ENHANCED LARGE-SCALE ASCENT WILL BE FAVORABLE FOR
LARGE HAIL AND WIND DAMAGE. CONSIDERING MID-LEVEL LAPSE RATE WILL
CONTINUE TO STEEPEN LATE THIS AFTERNOON AND MAY APPROACH 9.0 C/KM
ACROSS WEST TX...FAR NW OK...WRN KS...VERY LARGE HAIL ALSO APPEARS
LIKELY WITH THE MOST INTENSE SUPERCELLS. MODEL FORECASTS ORGANIZE A
LINE OF INTENSE STORMS ACROSS THE MODERATE RISK AREA MOVING THE LINE
EWD INTO WCNTRL KS...WRN OK AND WCNTRL TX OVERNIGHT. CONSIDERING THE
AMOUNT OF INSTABILITY IN PLACE...THE SEVERE THREAT MAY CONTINUE
AFTER MIDNIGHT ACROSS THE REGION.
..NRN PLAINS...
WATER VAPOR IMAGERY SHOWS AN UPPER-TROUGH OVER THE WRN U.S. WITH
SSWLY FLOW ALOFT OVER THE CNTRL HIGH PLAINS AND NRN PLAINS. SEVERAL
SUBTLE SHORTWAVE TROUGHS APPEAR TO BE LOCATED ACROSS THE REGION AND
LARGE-SCALE ASCENT WILL BE WIDESPREAD SUPPORTING NUMEROUS
THUNDERSTORM DEVELOPMENT LATE THIS AFTERNOON. IN
ADDITION...THUNDERSTORM COVERAGE WILL RAPIDLY INCREASE BY EARLY
EVENING ALONG THE WRN EDGE OF A STRENGTHENING LOW-LEVEL JET.
THUNDERSTORM COVERAGE SHOULD BE GREATEST FROM ECNTRL SD EXTENDING
SWWD INTO NCNTRL/NWRN NEB ALONG A FRONTAL BOUNDARY. IN
ADDITION...LIFT ACROSS THIS AREA WILL BE ENHANCED DUE TO THE LEFT
EXIT REGION OF THE MID-LEVEL JET.
FORECAST SOUNDINGS AND PROFILERS ACROSS THE REGION LATE THIS
AFTERNOON SHOW 0-6 KM SHEAR VALUES IN THE 50 TO 65 KT RANGE.
CONSIDERING MODERATE INSTABILITY IS IN PLACE SOUTH OF ABERDEEN
SD...SUPERCELL DEVELOPMENT WILL BE LIKELY UPON INITIATION. ALTHOUGH
STORM COVERAGE SHOULD BECOME QUITE NUMEROUS...A SUPERCELL THREAT
WILL CONTINUE THIS EVENING EVEN IF A LINEAR MCS DEVELOPS ACROSS THE
REGION. TORNADOES WILL BE POSSIBLE WITH THE BETTER-ORGANIZED
SUPERCELLS. IN ADDITION...OBJECTIVE ANALYSIS CURRENTLY SHOWS STEEP
LOW TO MID-LEVEL LAPSE RATES OF 7.0 TO 8.0 C/KM ACROSS MOST OF
SD...NRN NEB AND WRN NEB. THIS ALONG WITH THE STRONG VERTICAL SHEAR
SHOULD BE FAVORABLE FOR LARGE HAIL AND WIND DAMAGE. MLCAPE VALUES OF
1500 TO 2000 J/KG ALREADY EXIST AND INSTABILITY SHOULD CONTINUE TO
INCREASE FOR SEVERAL MORE HOURS. THIS COMBINED WITH THE STRONG
VERTICAL SHEAR...WIDESPREAD LIFT AND STEEP LAPSE RATES MAY BE ENOUGH
FOR VERY LARGE HAIL WITH THE MOST INTENSE SUPERCELLS MAINLY LATE
THIS AFTERNOON AND EARLY THIS EVENING. AS SFC TEMPS COOL TONIGHT...A
WARM LAYER NEAR 700 MB SHOWN ON SOME FORECAST SOUNDINGS MAY BECOME
PROBLEMATIC AND STORM COVERAGE SHOULD DECREASE ACROSS THE REGION.
.BROYLES.. 04/21/2007
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