Severe Thunderstorm Warning 49, NWS San Angelo, TX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
609 PM CDT WED APR 19 2006

.AVIATION...
ATMOSPHERE REMAINS UNSTABLE AS MOIST AIR OVERRIDES A COLD FRONT.
ACCAS OBSERVED OUTSIDE THE WEATHER OFFICE INDICATING MID LEVEL
INSTABILITY. COULD SEE TSTMS ANYTIME DURING THE NEXT 24
HOURS...BEST CHANCES FIRST AS WEAK SHORT WAVE APPROACHES FROM BIG
BEND THIS EVENING...SECOND AS UPPER SHORT WAVE APPROACHES FROM
WEST AFTER 15Z TOMORROW. WONT PUT TSRA IN TAFS AT KSJT OR
KABI...BUT WILL INDICATED VCTS OVERNIGHT. OTHERWISE LOOKING AT
MVFR CIGS BY MORNING AS COOLER/DRIER AIR AT SURFACE THINS OUT.

&&

.PREV DISCUSSION... (ISSUED 352 PM CDT WED APR 19 2006)

UPDATE...
UPDATED TO ADD SEVERE THUNDERSTORM WATCH NUMBER 211 TO W/W/A
SECTION. 20

PREV DISCUSSION... (ISSUED 316 PM CDT WED APR 19 2006)

SHORT TERM...
COLD FRONT THAT MOVED THROUGH OVERNIGHT HAS BEGUN TO RETREAT
SLOWLY BACK TO THE NORTH AS A WARM/STATIONARY FRONT THIS
AFTERNOON. TEMPERATURES SOUTH OF THE FRONT ARE IN THE LOWER 90S
WITH DEWPOINTS IN THE LOWER TO MID 60S...SO VERY UNSTABLE AIR
EXISTS TO THE SOUTH OF THIS BOUNDARY. CAN SEE CUMULUS DEVELOPING
ALONG AND SOUTH OF THIS BOUNDARY WITH A COUPLE SHOWERS CURRENTLY
ONGOING IN COLEMAN...BROWN...AND TOM GREEN COUNTIES. ALOFT...CAN
SEE A WEAK SHORTWAVE ROTATING AROUND THE UPPER LEVEL CLOSED LOW
MOVING INTO AZ. THIS SHORTWAVE WILL MOVE EAST/NORTHEAST INTO THE
AREA THIS EVENING. RUC DATA SHOWS MID LEVEL LAPSE RATES INCREASING
TO GREATER THAN 8C/KM ASSOCIATED WITH THIS WAVE. THIS WILL
INCREASE THE CHANCE FOR CONVECTION TO DEVELOP/SPREAD NORTHWARD
INTO OUR AREA FROM THE SLOWLY ADVANCING WARM FRONT. IN
ADDITION...THE LLJ IS EXPECTED TO INTENSIFY OVERNIGHT INCREASING
ISENTROPIC LIFT TO THE NORTH OF THE WARM FRONT. GFS AND NAM DATA
SHOW ELEVATED INSTABILITY AT THE 850MB LEVEL OF GREATER THAN
1000J/KG. IF CONVECTION CONTINUES TO DEVELOP...THIS INSTABILITY
COULD COMBINE WITH 0-6KM SHEAR VALUES AROUND 40KT AND RESULT IN
SEVERE THUNDERSTORMS WITH THE MAIN THREAT BEING LARGE HAIL.

LONG TERM...
FOR TOMORROW...WE ARE AGAIN LOOKING AT THE CHANCE FOR SEVERE
WEATHER FOR MUCH OF THE CWA. THERE MAY BE ONGOING CONVECTION OVER
NORTHERN AREAS INCLUDING THE BIG COUNTRY IF DEVELOPMENT CONTINUES
OVERNIGHT.

ALOFT...A VIGOROUS CLOSED LOW...NOW MOVING INTO AZ WILL OPEN UP
AND EJECT TO THE NORTHEAST ACROSS THE TX SOUTH PLAINS AND
PANHANDLE AREAS. AS THIS WAVE MOVES ACROSS... 0-6KM SHEAR VALUES
WILL INCREASE TO 45-55KT. MID LEVEL LAPSE RATES WILL ALSO INCREASE
TO GREATER THAN 8C/KM FOR AREAS NORTH OF AN OZONA TO BROWNWOOD
LINE AS THE BASE OF THE TROUGH MOVES ACROSS THE BIG COUNTRY. FLOW
WILL ALSO BECOME INCREASINGLY DIFFLUENT AHEAD OF THE LOW
THROUGHOUT THE DAY OVER MUCH OF TEXAS. AT THE SURFACE...MOISTURE
RETURN IS EXPECTED TO CONTINUE...AND TO POOL ALONG THE WARM FRONT
MOVING BACK TO THE NORTH...WHICH WILL BE ROUGHLY BISECTING OUR
CWA BY MID AFTERNOON. A SHARPENING DRYLINE WILL SURGE EAST DURING
THE AFTERNOON INTO OUR WESTERN COUNTIES BY MID AFTERNOON AS WELL.
SFC BASED CAPE VALUES OF 1500- 2000 J/KG WILL EXIST ALONG AND JUST
EAST OF THE DRYLINE. EXPECT NEW CONVECTION TO DEVELOP DURING THE
AFTERNOON EITHER ALONG THE DRYLINE OR IN THE WARM SECTOR BETWEEN
THE DRYLINE AND THE RETREATING WARM FRONT. WITH THE AMOUNT OF
INSTABILITY AND SHEAR AVAILABLE...EXPECT ANY THUNDERSTORMS THAT DO
DEVELOP TO QUICKLY BECOME SEVERE WITH ROTATING UPDRAFTS. ALTHOUGH
THE MAIN THREAT WILL BE LARGE HAIL...THERE WILL BE THE POTENTIAL
FOR TORNADOES WITH THUNDERSTORMS NEAR THE RETREATING WARM FRONTAL
BOUNDARY.

NORTHWEST FLOW ALOFT AND A SFC RIDGE WILL FOLLOW THE UPPER LEVEL
SHORTWAVE AS IT EXITS TO THE EAST FRIDAY. WILL CONTINUE TO HAVE A
CHANCE FOR PRECIPITATION INTO FRIDAY MORNING...BUT THINK THAT WITH
DRYING NORTHWEST FLOW...AND MORE STABLE BOUNDARY LAYER AIR MASS
MOVING IN THAT ANY LINGERING PRECIPITATION WILL QUICKLY EXIT THE
REGION DURING THE DAY. A WARMING TREND WILL FOLLOW FOR THE WEEKEND
WITH WINDS TURNING TO THE SOUTH AND SOUTHEAST. THERE WILL BE A
SLIGHT CHANCE FOR PRECIPITATION BEGINNING SATURDAY NIGHT AS WEAK
IMPULSES EJECT OUT TO THE NORTHEAST AHEAD OF ANOTHER LARGE UPPER
LEVEL TROUGH OVER THE WESTERN U.S. BY MONDAY AND TUESDAY...THE
MAIN TROUGH WILL APPROACH THE REGION...BRINGING THE BEST CHANCE
FOR RAIN TO THE AREA MONDAY NIGHT IF CURRENT TIMING HOLDS. WILL
HOLD POPS IN THE SLIGHT CHANCE CATEGORY FOR NOW HOWEVER WITH
THE AMOUNT OF UNCERTAINTY INHERENT IN ANY FORECAST 5-7 DAYS OUT.

SJT WATCHES/WARNINGS/ADVISORIES...
SEVERE THUNDERSTORM WATCH UNTIL 11 PM WEDNESDAY FOR THE
FOLLOWING ZONES: CONCHO...KIMBLE...MASON...MCCULLOCH...MENARD...
SAN SABA...SCHLEICHER...SUTTON...AND TOM GREEN.

&&

.SJT WATCHES/WARNINGS/ADVISORIES...
SEVERE THUNDERSTORM WATCH UNTIL 11 PM WEDNESDAY FOR THE
FOLLOWING ZONES: CONCHO...KIMBLE...MASON...MCCULLOCH...MENARD...
SAN SABA...SCHLEICHER...SUTTON...AND TOM GREEN.

&&

99/99/04

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE SAN ANGELO TX
317 PM CDT WED APR 19 2006

TXZ049-054-064>066-071>073-076>078-098-099-113-114-127-128-139-
140-154-155-168>170-202030-
FISHER-NOLAN-STERLING-COKE-RUNNELS-IRION-TOM GREEN-CONCHO-
CROCKETT-SCHLEICHER-SUTTON-HASKELL-THROCKMORTON-JONES-SHACKELFORD-
TAYLOR-CALLAHAN-COLEMAN-BROWN-MCCULLOCH-SAN SABA-MENARD-KIMBLE-
MASON-
317 PM CDT WED APR 19 2006

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF WEST CENTRAL
TEXAS.

.DAY ONE...THIS AFTERNOON AND TONIGHT

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND
TONIGHT. A STATIONARY FRONT STRETCHES FROM NORTH OF DEL RIO TO
TEMPLE AND EASTWARD TOWARDS LONGVIEW. SEVERE THUNDERSTORMS WILL
BE POSSIBLE ALONG THIS BOUNDARY THIS AFTERNOON AND TONIGHT.
INSTABILITY WILL BE STRONGEST SOUTH OF THE BOUNDARY WHERE LOW
LEVEL MOISTURE REMAINS IN PLACE. THE MAIN AREA OF CONCERN WILL BE
SOUTH OF I-10 ACROSS THE HILL COUNTRY AND EDWARDS PLATEAU. THE
MAIN THREATS WILL BE LARGE HAIL AND DAMAGING WINDS.

THUNDERSTORM ACTIVITY MAY INCREASE OVERNIGHT AS AN UPPER LEVEL
DISTURBANCE MOVES OVER THE REGION WITH THE STATIONARY FRONT
PUSHING NORTH AS A WARM FRONT. THIS ACTIVITY WILL BE ELEVATED
WITH ONLY HAIL AND DAMAGING WINDS AS THE THREATS. THE ACTIVITY
MAY AFFECT THE CONCHO VALLEY AND HEARTLAND EARLY IN THE NIGHT
WITH SOME ACTIVITY POSSIBLE PUSHING INTO THE BIG COUNTRY THURSDAY
MORNING.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER MUCH OF WEST
CENTRAL TEXAS ON THURSDAY. THE AFOREMENTIONED WARM FRONT IS
EXPECTED TO CONTINUE TO PUSH NORTH DURING THE DAY AS A STRONGER
UPPER LEVEL DISTURBANCE APPROACHES FROM NEW MEXICO. UPPER LEVEL
WINDS WILL INCREASE ALLOWING FOR DEEP LAYER SHEAR OF 50 KTS OVER
MUCH OF THE REGION. A DRYLINE WILL ALSO BEGIN TO SURGE EAST
DURING THE EARLY AFTERNOON AS THE WARM FRONT SLOWLY PUSHES NORTH.
THESE BOUNDARIES WILL PROVIDE THE FOCUS FOR SEVERE THUNDERSTORM
DEVELOPMENT. THE MAIN LIMITING FACTOR WILL BE HOW MUCH LOW LEVEL
MOISTURE RETURNS TO THE REGION SOUTH OF THE WARM FRONT. ASSUMING
ENOUGH MOISTURE INCREASES SOUTH OF THE FRONT...STRONG INSTABILITY
SHOULD DEVELOP AS WELL GIVEN ENOUGH DAYTIME HEATING. GIVEN STRONG
SHEAR AND ENOUGH INSTABILITY...SUPERCELL THUNDERSTORMS WILL BE
POSSIBLE ACROSS THE REGION WITH LARGE HAIL AND DAMAGING WINDS THE
MAIN THREATS. THERE EXISTS A SMALL THREAT FOR TORNADOES IF ANY
SUPERCELLS DEVELOP AND MOVE ALONG OR ACROSS THE WARM FRONT. THE
UNCERTAINTY IN THE SEVERE THUNDERSTORM POTENTIAL REMAINS DUE TO
HOW MUCH MOISTURE AND INSTABILITY RETURNS TO THE REGION.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED THIS AFTERNOON ALONG AND SOUTH
OF I-10. SPOTTER ACTIVATION MAY BE REQUIRED FOR MUCH OF WEST
CENTRAL TEXAS ON THURSDAY. SPOTTERS ARE ENCOURAGED TO MONITOR THE
LATEST FORECASTS AND UPDATES TO THE SEVERE WEATHER POTENTIAL.

10

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