STORM2K

Severe Thunderstorm Watch

SEVERE THUNDERSTORM WATCH OUTLINE UPDATE FOR WS 824
NWS STORM PREDICTION CENTER NORMAN OK
120 PM CDT THU OCT 12 2006

SEVERE THUNDERSTORM WATCH 824 IS IN EFFECT UNTIL 900 PM CDT
FOR THE FOLLOWING LOCATIONS

TXC007-015-021-039-041-051-055-057-071-089-123-149-157-167-175-
177-185-199-201-239-241-245-285-287-291-321-339-351-361-373-391-
407-457-469-471-473-477-481-130200-
/O.NEW.KWNS.SV.A.0824.061012T1820Z-061013T0200Z/

TX
. TEXAS COUNTIES INCLUDED ARE

ARANSAS AUSTIN BASTROP
BRAZORIA BRAZOS BURLESON
CALDWELL CALHOUN CHAMBERS
COLORADO DEWITT FAYETTE
FORT BEND GALVESTON GOLIAD
GONZALES GRIMES HARDIN
HARRIS JACKSON JASPER
JEFFERSON LAVACA LEE
LIBERTY MATAGORDA MONTGOMERY
NEWTON ORANGE POLK
REFUGIO SAN JACINTO TYLER
VICTORIA WALKER WALLER
WASHINGTON WHARTON
$$

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 824
NWS STORM PREDICTION CENTER NORMAN OK
120 PM CDT THU OCT 12 2006

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

PARTS OF SOUTH CENTRAL AND SOUTHEAST TEXAS COASTAL WATERS

EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 120 PM UNTIL 900 PM CDT.

HAIL TO 2.5 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 80 STATUTE MILES NORTH AND SOUTH OF A LINE FROM 15 MILES EAST NORTHEAST OF PORT ARTHUR TEXAS TO 45 MILES WEST NORTHWEST OF VICTORIA TEXAS. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU4).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY DO PRODUCE TORNADOES.

DISCUSSION...VERY MOIST...MODERATELY UNSTABLE AIRMASS IN PLACE S OF ADVANCING COLD FRONT IN CENTRAL TX. DEEP LAYER SHEAR SUPPORTS BOTH MULTICELLULAR AND ISOLATED SUPERCELLS IN THE AIR MASS ACROSS THE WATCH. STORMS WILL INCREASE IN NUMBER AND INTENSITY REMAINDER OF AFTERNOON ALONG AND AHEAD OF COLD FRONT WITH LARGE HAIL/DAMAGING WINDS THE PRIMARY THREAT...PARTICULARLY ASSOCIATED WITH ANY SUPERCELL.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 550. MEAN STORM MOTION VECTOR 28025.

Update from Jeff....



SPC has issued a Severe Thunderstorm Watch until 900pm for SE TX .

Discussion:

Moist and unstable air mass igniting rapidly with surface heating and incoming frontal boundary. Meso-boundary along the coast is adding low level shear with large tornadic supercells showing good low level rotation over Brazoria Co. Cold front is just N of the region moving S at 20mph.

Air mass characteristics and shear values favor a severe and tornado threat through the afternoon as the front crosses the area. Main threats will be strong winds and tornadoes although the main tornado threat appears to be confined along the coast from Galveston Island to Sugarland and SW where air mass is extremely moist. Squall line may develop and fill along incoming front with numerous supercells developing/ongoing south of the boundary.

SPC 3pm update:

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF SE TX AND FAR
SW LA...

...SE TX/FAR SW LA...
A STRONG UPPER-LEVEL LOW AND BROAD UPPER-LEVEL TROUGH OVER THE CNTRL
AND ERN U.S. WILL REMAIN IN PLACE TODAY. AT THE SFC...A COLD FRONT
EXTENDING EAST TO WEST FROM CNTRL LA INTO CNTRL TX WILL MOVE SLOWLY
SWD THIS AFTERNOON. LATEST ANALYSIS SHOWS SFC DEWPOINTS SOUTH OF THE
BOUNDARY IN THE LOWER TO MID 70S F AND MODERATE INSTABILITY IS
PRESENT ACROSS MOST OF THE WARM SECTOR. THIS COMBINED WITH
INCREASING LOW-LEVEL CONVERGENCE SHOULD HELP STORM COVERAGE TO
EXPAND THIS AFTERNOON ACROSS THE REGION.

THIS THUNDERSTORM ACTIVITY IS LOCATED ON THE SRN PERIPHERY OF AN
IMPRESSIVE 110 KT MID-LEVEL JET ROTATING AROUND THE ECNTRL U.S.
UPPER-LEVEL TROUGH. THE LATEST WSR-88D VWPS FROM THE HOUSTON AREA
SHOW VEERING LOW-LEVEL WINDS WITH WLY FLOW OF 40-45 KT AT 6 KM
SUGGESTING VERTICAL SHEAR WILL SUPPORT ISOLATED SUPERCELLS ACROSS SE
TX AND FAR SW LA THIS AFTERNOON. RUC AND NAM FORECASTS INCREASE A
25-35 KT LOW-LEVEL JET ACROSS SE TX WHICH SHOULD REINFORCE LOW-LEVEL
SHEAR PROFILES RESULTING IN AN ISOLATED TORNADO THREAT AS SUPERCELLS
DEVELOP LATE THIS AFTERNOON. DAMAGING WINDS AND/OR HAIL WILL ALSO BE
POSSIBLE WITH SUPERCELLS AND THE STRONGER CELLS WITHIN SHORT-LINE
SEGMENTS ESPECIALLY IN AREAS WITH LOCALLY STEEP LOW-LEVEL LAPSE
RATES.

MESOSCALE DISCUSSION 2107
NWS STORM PREDICTION CENTER NORMAN OK
0608 PM CDT THU OCT 12 2006

AREAS AFFECTED...SERN TX...SWRN LA

CONCERNING...SEVERE THUNDERSTORM WATCH 824...

VALID 122308Z - 130015Z

PERSISTENT CONVECTION AND EXTENSIVE OUTFLOW CONTAMINATION ACROSS
UPPER COASTAL PLAINS OF TX HAS EFFECTIVELY STABILIZED THE BOUNDARY
LAYER...MLCAPE VALUES LESS THAN 500 J/KG. THUNDERSTORMS REMAIN
CONCENTRATED ALONG TWO LOW LEVEL CONVERGENT ZONES...THE FIRST IS THE
LEADING OUTFLOW BOUNDARY FROM OFF THE COAST...NWWD TO LAVACA COUNTY.
THE SECOND AXIS OF CONCENTRATION IS ALONG THE ADVANCING COLD FRONT
ACROSS NRN PORTIONS OF THE WATCH. ADDITIONALLY...IT APPEARS WEAK
WARM ADVECTION WILL ASSIST THUNDERSTORM ACTIVITY FOR THE NEXT
SEVERAL HOURS ACROSS CNTRL/WRN PORTIONS OF THE WATCH WHERE WLY FLOW
ALOFT WILL SPREAD STEEPER LAPSE RATE/INSTABILITY ENVIRONMENT ATOP
COOLER LOW LEVEL AIRMASS. EVEN SO OVERALL TRENDS SUGGEST GREATEST
RISK OF SEVERE WILL BE ISOLATED LARGE HAIL WITH ANY DEVIANT
SUPERCELL STRUCTURES.

..DARROW.. 10/12/2006

Severe Thunderstorm Warning

SEVERE THUNDERSTORM WARNING
TXC015-089-157-481-130115-
/O.NEW.KHGX.SV.W.0155.061013T0037Z-061013T0115Z/

BULLETIN - EAS ACTIVATION REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
740 PM CDT THU OCT 12 2006

THE NATIONAL WEATHER SERVICE IN LEAGUE CITY HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...
WHARTON COUNTY IN SOUTHEAST TEXAS
FORT BEND COUNTY IN SOUTHEAST TEXAS
COLORADO COUNTY IN SOUTHEAST TEXAS
AUSTIN COUNTY IN SOUTHEAST TEXAS

* UNTIL 815 PM CDT

* AT 733 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
A SEVERE THUNDERSTORM CAPABLE OF PRODUCING PENNY SIZE HAIL.
THIS STORM WAS LOCATED NEAR WALLIS...MOVING SOUTHEAST AT 25 MPH.

* LOCATIONS IMPACTED INCLUDE...
SEALY...WALLIS...SIMONTON...