Hail and Damaging Winds in Texas, March 25, 2009

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
723 PM CDT WED MAR 25 2009

.DISCUSSION...

SPC HAS ISSUED A TORNADO WATCH 65 FOR THE SOUTHERN HALF OF THE CWA
THRU 06Z.

AN EXPANDING COLD POOL AND AN OUTFLOW BOUNDARY COUPLED WITH A
RESIDUAL BOUNDARY WILL SET THE STAGE FOR AN ACTIVE EVENING. AT
THIS TIME...IT LOOKS LIKE THE CONVECTION OUT WEST WILL CONTINUE TO
PUSH EAST AND CROSS THE ENTIRE CWA BY 11 PM. SOUTHWEST COUNTIES OF
JACKSON AND MATAGORDA ARE MORE CAPPED AND MIGHT MISS THIS EVENT.
HAVE UPPED POPS AND LOWERED TEMPS PER CURRENT OBS. NEW ZONES
ALREADY OUT. 43

&&

.PREV DISCUSSION... /ISSUED 710 PM CDT WED MAR 25 2009/

DISCUSSION...
AVIATION UPDATE...SEE BELOW.

AVIATION...
A LINE OF STRONG THUNDERSTORMS...WITH ISOLATED SEVERE STORMS...
WILL AFFECT THE NORTHERN SET OF TERMINALS THIS EVENING. THE NAM
MODEL DID NOT VERIFY WELL WHILE THE GFS WAS DOING QUITE WELL
THROUGH 00Z. STORMS WERE TRYING TO BUILD SOUTHWESTWARD ALONG THE
LINE. IF THIS OCCURS...THE REMAINING SITES SOUTH OF THE BIG
AIRPORTS WILL LIKELY EXPERIENCE THUNDERSTORMS. FOR NOW WILL KEEP
THE HIGHEST WIND GUST FORECASTS FROM KIAH NORTHWARD. WILL UPDATE
BY 03Z FOR THE SOUTHERN SET IF THE STORMS DEVELOP SOUTHWARD.

OTHERWISE...THE MODELS WERE DEVELOPING IFR CONDITIONS OVER ALL
SITES LATER TONIGHT. FELT THAT THIS WAS OVERDONE...ESPECIALLY AT
KCLL AND KUTS WHERE VFR CEILINGS ARE POSSIBLE FOR MOST OF THE
OVERNIGHT PERIOD. BOTH LOCATIONS WILL LIKELY REMAIN BEHIND THE
FRONT. FURTHER TO THE SOUTH AM EXPECTING MVFR CONDITIONS WITH SOME
IFR AREAS MAINLY SOUTH OF INTERSTATE 10. CONFIDENCE IS SHAKY WITH
THIS PORTION OF THE FORECAST.

FOR THURSDAY A REPEAT OF TODAY IS LIKELY. MVFR CEILINGS IN THE
MORNING WILL LEAD INTO THUNDERSTORM CHANCES DURING THE AFTERNOON.
BEST CHANCES WILL BE ACROSS KCLL AND KUTS. WENT WITH VCTS FROM
METRO HOUSTON SOUTH TO THE COAST.

40

PREV DISCUSSION... /ISSUED 326 PM CDT WED MAR 25 2009/

DISCUSSION...
SPC HAS ISSUED TORNADO WATCH #63 FOR THE NORTHERN HALF OF THE CWA
EFFECTIVE UNTIL 02Z. SFC FRONT HAS RETREATED NORTH TO NEAR A LA
GRANGE...IAH...BEAUMONT LINE WITH SHALLOW COOL AIR QUICKLY
ERODING. FRONT WILL CONTINUE TO ERODE NORTH THIS AFTN AND WILL
PROBABLY STALL AGAIN EARLY EVENING OVER OUR NRN ZONES. LIFT WILL
INCREASE ACROSS SE TX OVER THE NEXT FEW HOURS AS SHORTWAVE
APPROACHES FROM THE WEST AND SE TX GOES INTO LEFT FRONT QUAD OF
UPPER JET. TSRA NOW DEVELOPING OVER THE EDWARDS PLATEAU/HILL
COUNTRY REGION WILL SPREAD EAST ACROSS OUR NRN ZONES THIS EVENING.
MAIN THREAT OF SEVERE WEATHER WILL BE ALONG AND NORTH OF THE WARM
FRONT...WITH CAPPING LIKELY TO LIMIT DEVELOPMENT TO THE SOUTH OF
THE BOUNDARY. WILL CONTINUE TO MENTION SEVERE FOR WHOLE AREA IN
HWO...BUT CONFIDENCE IS HIGHEST NORTH OF I-10. TSRA SHOULD END
AROUND MIDNIGHT AS SHORTWAVE PUSHES EAST OF THE AREA. ONGOING
CONVECTION WILL LIKELY REINFORCE THE BOUNDARY AND PUSH IT BACK TO
THE SOUTH THIS EVENING. CWA WILL SEE ONLY A SHORT BREAK IN THE
ACTION LATE TONIGHT/EARLY THURSDAY. BOTH NAM/GFS SHOW ANOTHER
DISTURBANCE PUSHING THROUGH SE TX THU AFTN. FLOW ALOFT WILL REMAIN
DIFFLUENT AS SE TX REMAINS IN THE LEFT FRONT QUAD OF A 100 KT
UPPER JET. MOISTURE WILL REMAIN PLENTIFUL WITH PWS IN THE 1.4-1.6
INCH RANGE. MID LEVELS WILL COOL FURTHER WITH THIS DISTURBANCE
SETTING UP VERY STEEP LAPSE RATES. GFS BUFR SOUNDINGS FORECAST
WEAK CAPPING THURSDAY...LIS OF -7 TO -10...CAPES >2500 J/KG...AND
CONVECTIVE TEMPS ONLY IN THE MID 70S. EXPECT ANOTHER ROUND OF
SCATTERED CONVECTION THURSDAY AFTN/EVENING WITH SEVERE POTENTIAL
ONCE AGAIN. THURSDAY SEEMS MORE CLEAR CUT THAN TODAY...A WEAKER
CAP...COLDER TEMPS ALOFT AND MORE INSTABILITY. THIS DISTURBANCE
WILL PUSH EAST OF THE AREA THU EVENING ENDING THE SEVERE THREAT.

STRONG UPPER LOW WILL DIG SOUTH ACROSS NEW MEXICO FRIDAY AND PUSH
EAST ACROSS THE RED RIVER VALLEY FRI NIGHT. FOLLOWED THE NAM/ECMWF
WITH THIS SYSTEM WHICH ARE A BIT SLOWER THAN THE GFS. SFC DRYLINE
WILL PUSH INTO SE TX FRIDAY. AT THIS POINT THE DEEP MOISTURE (1.5
INCH PWS) WILL BE CONFINED TO THE EASTERN HALF OF THE CWA.
IMPRESSIVE DYNAMICS WILL RESULT IN TSRA DEVELOPMENT ALONG THE
DRYLINE FRIDAY... BUT SE TX WILL LIKELY BE IN THE INITIATION ZONE.
HAVE KEPT POPS IN THE WEST ON THE LOW SIDE (20S/30S). STORMS
SHOULD QUICKLY EXIT THE AREA BY SUNSET. STRONG COLD FRONT WILL
SWEEP THROUGH THE AREA FRI EVENING. SOME WRAP AROUND LOW CLOUDS
AND MAYBE EVEN A FEW LIGHT SHOWERS WILL AFFECT NRN ZONES LATE FRI
NIGHT/SATURDAY...WITH BREEZY CONDITIONS AREA WIDE. SNOW COVER WILL
BE PRESENT TO OUR NORTH AND MODELS FORECAST IMPRESSIVE COLD
ADVECTION IN THE WAKE OF THIS FRONT. HAVE FURTHER LOWERED TEMPS
FRI NIGHT THROUGH SATURDAY NIGHT. IT IS ENTIRELY IN THE REALM OF
POSSIBILITY THAT THE NE ZONES WILL SEE PATCHY FROST OR MAYBE EVEN
A LIGHT FREEZE SAT NIGHT. TEMPS WILL QUICKLY MODIFY SUNDAY THROUGH
MONDAY AS ONSHORE FLOW RETURNS. A WEAK COLD FRONT WILL CROSS THE
AREA MON NIGHT...BUT KEPT FCST DRY AS MOISTURE WILL REMAIN
SHALLOW.

35

MARINE...
SEAS RUNNING 3 TO 6 FEET ACROSS UPPER TEXAS COASTAL WATERS. LONG
SOUTH TO SOUTHEAST FETCH PREVAILING ACROSS WESTERN GULF AND
MODERATE FLOW WILL CONTINUE. WINDS INDICATED TO INCREASE SLIGHTLY
TONIGHT ALONG WITH SLIGHT INCREASE IN WAVE HEIGHTS FOR 20 TO 60 NM
REGION. WILL HOIST SCA FOR AFOREMENTIONED REGION FROM LATE EVENING
TO REST OF NIGHT. ONSHORE FLOW STRENGTHENING THURSDAY NIGHT BEFORE
WEAKENING AHEAD OF COLD FRONT WHICH IS EXPECTED TO MOVE ACROSS
COASTAL WATERS FRIDAY EVENING. THIS FRONT WILL USHER A STRONG
OFFSHORE FLOW WHICH MAY NOT MODERATE UNTIL LATE SATURDAY. 37

&&

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      55  80  67  81  41 /  80  60  20  30  20
HOUSTON (IAH)              63  80  68  81  44 /  80  50  30  40  20
GALVESTON (GLS)            64  76  70  78  50 /  20  40  20  30  20

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT ADVISORY UNTIL 7 AM CDT THURSDAY FOR THE FOLLOWING
     ZONES: WATERS FROM FREEPORT TO THE MATAGORDA SHIP CHANNEL
     20 NM TO 60 NM...WATERS FROM HIGH ISLAND TO FREEPORT 20 TO
     60 NM.

     SMALL CRAFT SHOULD EXERCISE CAUTION UNTIL 10 PM CDT THIS EVENING
     FOR THE FOLLOWING ZONES: WATERS FROM FREEPORT TO THE
     MATAGORDA SHIP CHANNEL 20 NM TO 60 NM...WATERS FROM HIGH
     ISLAND TO FREEPORT 20 TO 60 NM.

&&

DISCUSSION...43

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
341 PM CDT WED MAR 25 2009

GMZ330-335-350-355-370-375-TXZ163-164-176>179-195>200-210>214-226-
227-235>238-261200-
AUSTIN-BRAZORIA-BRAZOS-BURLESON-CHAMBERS-COLORADO-FORT BEND-
GALVESTON-GALVESTON BAY-GRIMES-HARRIS-HOUSTON-JACKSON-LIBERTY-
MADISON-MATAGORDA-MATAGORDA BAY-MONTGOMERY-POLK-SAN JACINTO-
TRINITY-WALKER-WALLER-WASHINGTON-
WATERS FROM FREEPORT TO THE MATAGORDA SHIP CHANNEL 20 NM TO 60 NM-
WATERS FROM FREEPORT TO THE MATAGORDA SHIP CHANNEL OUT 20 NM-
WATERS FROM HIGH ISLAND TO FREEPORT 20 TO 60 NM-
WATERS FROM HIGH ISLAND TO FREEPORT OUT 20 NM-WHARTON-
341 PM CDT WED MAR 25 2009

...SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS ALL OF SOUTHEAST
TEXAS THIS EVENING AND AGAIN THURSDAY...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHEAST TEXAS.

.DAY ONE...REST OF THIS AFTERNOON AND TONIGHT

A STALLED FRONT DRAPED WEST TO EAST ACROSS THE CENTRAL PORTIONS OF
THE AREA WILL STALL AGAIN THIS EVENING ACROSS THE NORTHERN
COUNTIES OF SOUTHEAST TEXAS. SCATTERED THUNDERSTORMS DEVELOPING
OVER THE EDWARDS PLATEAU AND HILL COUNTRY ARE EXPECTED TO SPREAD
EAST INTO THE AREA AFTER 6 PM AS AN UPPER LEVEL DISTURBANCE
APPROACHES FROM THE WEST.

THE BULK OF THE THUNDERSTORM ACTIVITY IS EXPECTED TO DEVELOP
NORTH OF THE FRONT. THE POTENTIAL EXISTS FOR A FEW OF THESE
STORMS TO BECOME SEVERE...WITH THE GREATEST SEVERE WEATHER
POTENTIAL NORTH OF INTERSTATE 10. ANY STORMS THAT BECOME SEVERE
WILL HAVE THE POTENTIAL TO PRODUCE LARGE HAIL...DAMAGING
WINDS...AND ISOLATED TORNADOES. IN ADDITION...LOCALLY HEAVY
RAINFALL WILL BE POSSIBLE. RAINFALL AMOUNTS WILL AVERAGE 1/2 TO 1
INCH WITH ISOLATED HIGHER TOTALS.

SOUTH OF THE FRONT...LESS THUNDERSTORM COVERAGE IS
EXPECTED DUE TO A CAPPING LAYER OF WARM AIR IN THE ATMOSPHERE.
HOWEVER...ANY STORMS THAT MANAGE TO BREAK THE CAP SOUTH OF THE
FRONT WILL ALSO HAVE THE POTENTIAL TO BECOME SEVERE.

THE SEVERE WEATHER THREAT IS EXPECTED TO END BY MIDNIGHT AS THE
UPPER LEVEL DISTURBANCE MOVES EAST OF THE AREA.

.DAY TWO...THURSDAY AND THURSDAY NIGHT

ANOTHER UPPER LEVEL DISTURBANCE IS EXPECTED TO CROSS SOUTHEAST
TEXAS THURSDAY AFTERNOON. THIS DISTURBANCE WILL COMBINE WITH THE
MOIST AND UNSTABLE AIRMASS IN PLACE TO GENERATE SCATTERED SHOWERS
AND THUNDERSTORMS. THE AIRMASS IS EXPECTED TO BECOME STRONGLY
UNSTABLE OVER THE AREA THURSDAY AFTERNOON...WITH CAPPING LESS OF
AN ISSUE THAN TODAY. THE COMBINATION OF THE STRONG INSTABILITY AND
LOW LEVEL SHEAR WILL FAVOR THE POTENTIAL FOR ISOLATED SUPERCELLS
PRODUCING LARGE HAIL...DAMAGING WINDS...OR ISOLATED TORNADOES.

.DAY THREE...FRIDAY THROUGH FRIDAY NIGHT

A COLD FRONT WILL TREK ACROSS SOUTHEASTERN TEXAS THROUGH THE
DAYTIME HOURS...REACHING THE COAST AROUND SUNSET. SCATTERED
THUNDERSTORMS MAY DEVELOP AHEAD OF THE MAIN SURFACE FRONT...OR
OVER THE EASTERN HALF OF SOUTHEAST TEXAS. THERE IS A SMALL WINDOW
OF POSSIBILITY FOR A FEW SEVERE STORMS OVER THE EASTERN HALF OF
SOUTHEAST TEXAS FROM MIDDAY THROUGH MID AFTERNOON FRIDAY.

.DAYS FOUR THROUGH SEVEN...SATURDAY THROUGH TUESDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS POSSIBLE TODAY...THURSDAY...AND FRIDAY.