Friday, April 20, 2007

DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 201712
SWODY2
SPC AC 201711

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1211 PM CDT FRI APR 20 2007

VALID 211200Z - 221200Z

..THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF WEST TX AND WRN
KS...

..THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE SRN
PLAINS...CNTRL HIGH PLAINS AND NRN PLAINS...

..SEVERE THUNDERSTORM OUTBREAK POSSIBLE SATURDAY ACROSS PARTS OF
THE GREAT PLAINS ESPECIALLY ACROSS PARTS OF WEST TX AND WRN KS...

..SRN AND CNTRL PLAINS...
LATEST WATER VAPOR IMAGERY SHOWS A WELL-DEFINED UPPER-LEVEL TROUGH
AND CLOSED-OFF LOW JUST OFF THE CALIFORNIA COAST. THIS SYSTEM IS
FORECAST TO MOVE EWD ACROSS THE ROCKIES TONIGHT SPREADING STRONG
LARGE-SCALE ASCENT INTO THE SRN AND CNTRL PLAINS SATURDAY. IN
ADDITION...LOW-LEVEL MOISTURE...INSTABILITY AND SHEAR PROFILES SHOWN
ON MODEL FORECASTS AND FORECAST SOUNDINGS WILL BE ADEQUATE FOR
WIDESPREAD SEVERE THUNDERSTORMS SATURDAY AFTERNOON AND EVENING.
THUNDERSTORMS WILL DEVELOP ALONG A DRYLINE SATURDAY AFTERNOON AND
EXPAND IN COVERAGE ACROSS THE REGION LATE SATURDAY AFTERNOON INTO
THE EVENING. ALTHOUGH THERE ARE MINOR DIFFERENCES IN THE LAST THREE
RUNS OF THE NAM MODEL...THE OVERALL SOLUTIONS ARE RELATIVELY
CONSISTENT SUGGESTING CONFIDENCE IN WIDESPREAD SEVERE WEATHER
SATURDAY ACROSS THE WRN PORTION OF THE SRN AND CNTRL PLAINS IS HIGH
ATTM.

SOME UNCERTAINTIES STILL REMAIN INCLUDING CONVECTIVE MODE AND SEVERE
WEATHER REPORT TYPE. FORECAST SOUNDINGS ACROSS THE REGION SATURDAY
AFTERNOON SHOW 0-6 KM SHEAR VALUES IN THE 55 TO 75 KT RANGE ALONG
WITH MODERATE INSTABILITY SUGGEST SUPERCELLS WILL DEVELOP QUICKLY
AFTER INITIATION ALONG A NARROW AXIS JUST EAST OF THE DRYLINE. DUE
TO THE STRONG FORCING ASSOCIATED WITH THE APPROACHING
UPPER-TROUGH...THUNDERSTORM DEVELOPMENT SHOULD BE QUITE NUMEROUS
MAINLY FROM THE LUBBOCK AREA NWD ACROSS THE TX PANHANDLE INTO WRN
KS. A THREAT FOR TORNADOES...LARGE HAIL AND WIND DAMAGE WILL BE
LIKELY WITH SUPERCELLS ESPECIALLY AS THUNDERSTORMS INITIATE AND
MATURE SATURDAY AFTERNOON.

THE THREAT FOR SIGNIFICANT TORNADOES ACROSS THE REGION STILL REMAINS
UNCLEAR BECAUSE LOW-LEVEL WIND PROFILES SHOWN ON FORECAST SOUNDINGS
SHOULD BE SOMEWHAT BACKED EVEN TO 850 MB SATURDAY AFTERNOON.
HOWEVER...IF SUPERCELLS REMAIN DISCRETE FOR A LONG ENOUGH TIME...A
CLUSTER OF TORNADOES COULD OCCUR AND WOULD BE MOST LIKELY WWD FROM
THE LOW-LEVEL JET ACROSS THE TX PANHANDLE AND ON THE CAPROCK IN THE
VICINITY OF LUBBOCK. IF THUNDERSTORMS CONGEAL BY EARLY EVENING INTO
A LARGE LINEAR MCS WHICH MODEL FORECASTS SUGGEST MAY OCCUR...THEN
THE THREAT SHOULD TRANSITION TO MOSTLY LARGE HAIL AND WIND DAMAGE.
STEEP LAPSE RATES...MODERATE INSTABILITY AND STRONG VERTICAL SHEAR
PROFILES ON FORECAST SOUNDINGS COULD ALSO BE FAVORABLE FOR LARGE
HAIL OF AT LEAST TWO INCH DIAMETER AND A FEW VERY STRONG WIND GUSTS
SATURDAY AFTERNOON AND EVENING. ALTHOUGH THE SIGNIFICANT TORNADO
THREAT MAY BE SLIGHTLY LESS ACROSS WRN KS DUE TO THE POSITION OF THE
LOW-LEVEL JET MAXIMA...DAMAGING LARGE HAIL AND VERY STRONG WIND
GUSTS MAY ALSO OCCUR IN THAT PORTION OF THE MODERATE RISK. ANY
SEVERE THREAT MAY CONTINUE INTO THE OVERNIGHT PERIOD BUT SHOULD
BECOME MORE ISOLATED AS INSTABILITY DECREASES ACROSS THE REGION.

..NRN PLAINS...
LATEST WATER VAPOR IMAGERY SHOWS AN UPPER-LEVEL TROUGH ALONG THE
WEST COAST. THIS FEATURE WILL MOVE EWD ACROSS THE WRN U.S. AND INTO
THE ROCKIES SATURDAY. AHEAD OF THE SYSTEM...LOW-LEVEL MOISTURE WILL
INCREASE ACROSS THE NRN PLAINS WHICH SHOULD BE SUFFICIENT FOR
MODERATE INSTABILITY BY SATURDAY AFTERNOON. IN ADDITION...SUBTLE
SHORTWAVE ACTIVITY AHEAD OF THE UPPER-TROUGH SHOULD MOVE NNEWD
ACROSS THE REGION PROVIDING LARGE-SCALE ASCENT SUFFICIENT FOR
SCATTERED THUNDERSTORM DEVELOPMENT SATURDAY AFTERNOON AND EVENING.

FORECAST SOUNDINGS ACROSS THE NRN PLAINS SATURDAY AFTERNOON SHOW 0-6
KM SHEAR VALUES IN THE 45 TO 60 KT RANGE SUGGESTING SUPERCELL
DEVELOPMENT WILL BE LIKELY AS THUNDERSTORMS INITIATE IN THE
AFTERNOON. STEEP LAPSE RATES AND STRONG LOW-LEVEL FLOW SHOULD BE
CONDUCIVE FOR LARGE HAIL AND WIND DAMAGE SATURDAY AFTERNOON AND
EVENING ESPECIALLY IF A LINEAR MCS ORGANIZES BY EARLY EVENING.
TORNADOES ALSO APPEAR POSSIBLE WITH THE BETTER ORGANIZED SUPERCELLS
ESPECIALLY SINCE THE LOW-LEVEL JET HAS BECOME MORE DISTINCT IN THE
LATEST MODEL FORECASTS RUNS. THE SEVERE THREAT COVERAGE MAY BE
SUFFICIENT FOR A MODERATE RISK ACROSS PARTS OF THE REGION.
HOWEVER...UNCERTAINTY REMAINS TOO HIGH ESPECIALLY CONCERNING THE
QUALITY OF MOISTURE RETURN AND THUNDERSTORM COVERAGE FOR AN UPGRADE
ATTM.

.BROYLES.. 04/20/2007

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