Flash Flooding in Texas, June 19, 2006

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1141 PM CDT SUN JUN 18 2006

.UPDATE...
HAVE LOWERED RAIN CHANCES NORTH AS MID LEVEL CIRCULATION/MCV
WEAKER LOOKING NOW AND JUST SLIGHTLY FURTHER EAST THAN PREVIOUS
THINKING. MODELS STILL SAGGING THIS FEATURE SLOWLY SOUTHWESTWARD
WITH DECENT INFLOW ACROSS THE COASTAL AND SOUTHEAST ZONES WITH PW
OF >1.6-1.8. EXPECTING TO SEE CURRENT BAND OF STORMS TO BACKBUILD
INTO HARRIS COUNTY.  LOOKS AS THOUGH THE GREATER RAIN THREAT
SHOULD BE FOR AREAS FROM WHARTON TO HARRIS TO POLK COUNTY AND
GREATEST FLOOD THREAT WILL BE ACROSS FORT BEND TO HARRIS TO
LIBERTY AND CHAMBERS COUNTIES. HAVE PARED BACK THE FLOOD WATCH
COUNTIES AND IT SHOULD BE OUT VERY SHORTLY. STILL THINK THAT
RAINFALL AMOUNTS IN EXCESS OF 6 INCHES POSSIBLE THE REMAINDER OF
TONIGHT AND INTO MONDAY.

45/38

&&

.PREV DISCUSSION... (ISSUED 616 PM CDT SUN JUN 18 2006)

UPDATE...
LOOKS LIKE SOME BIG RAINS ON THE WAY. WILL BE HOISTING A FLOOD
WATCH FOR MOST OF THE AREA (MAINLY SE 2/3RDS OF THE REGION)...VERY
IMPRESSIVE FF SCENARIO IN THE WORKS. ABUNDANT CAPE >1500...PW
ADVECTING IN FROM THE GULF OF 1.9-2.05 AND A SLOW MOVING MID-
LEVEL CIRCULATION THAT SHOULD BE DRIFTING SOUTHWEST LEADING TO
PERSISTENT LL FLOW OF MOISTURE INTO THE BOUNDARY OVER THE CENTRAL
TIER OF COUNTIES.

WILL HAVE THE FLOOD WATCH AND UPDATED ZFP OUT SHORTLY.

45/38

PREV DISCUSSION... (ISSUED 250 PM CDT SUN JUN 18 2006)

DISCUSSION...
SURFACE ANALYSIS SHOWS AN OUTFLOW BOUNDARY LEFT OVER FROM THIS
MORNINGS MCS EXTENDING FROM JUST WEST OF LUFKIN SOUTH TO NEAR
KIAH SOUTHWEST INTO WHARTON COUNTY. LOW LEVEL CONVERGENCE WAS
BEGINNING TO INITIATE SHRA DEVELOPMENT ALONG AND JUST EAST OF THE
OUTFLOW AT 19Z. EXPECT THIS ACTIVITY TO PERSIST THROUGH SUNSET MAINLY
OVER THE FAR EASTERN AND SOUTHERN PORTIONS OF THE CWA.

SATELLITE IMAGERY CLEARLY SHOWS THE MID/UPPER LEVEL LOW CENTERED
OVER THE FAR NRN PORTIONS OF THE CWA. MODELS HAVE BEEN VERY
INCONSISTENT WITH THEIR HANDLING OF THIS SYSTEM FROM RUN TO RUN. 12Z
RUNS OF THE GFS/NAM HAVE SWITCHED BACK TO MUCH WETTER SOLUTIONS FOR
THE FIRST 24-36 HOURS...WITH A SLOWER TRACK THAN THE LAST COUPLE OF
RUNS. HPC HAS BEEFED UP THEIR QPF FORECASTS FOR TONIGHT/MONDAY OVER
CONCERNS THAT THE UPPER LOW MAY STALL OVER SE TX DURING THE PERIOD
GENERATING ANOTHER ROUND OF HEAVY RAINS FOR THE AREA. THESE CONCERNS
SEEM JUSTIFIED GIVEN CURRENT SATTELITE TRENDS...AS SYSTEM HAS MOVED
VERY LITTLE TODAY AND APPEARS IT COULD TRACK DIRECTLY SOUTH OVER THE
AREA (A LITTLE WEST OF WHAT MODELS ARE FORECASTING). THESE SYSTEMS
HAVE A TENDENCY TO PRODUCE HEAVY RAINS ESPECIALLY IN THE LATE NIGHT
AND MORNING HOURS WHEN STRENGTHENING LOW LEVEL INFLOW FEEDS HIGH PW
AIR INTO THE SYSTEM AND STRONG LIFT IS FOCUSED OVER A SMALLER AREA
NEAR THE CORE OF THE UPPER LOW. PLENTY OF MOISTURE IS STILL
AVAILABLE FOR THIS SYSTEM TO TAP INTO WITH SFC DEWPOINTS IN THE
MID/UPPER 70S ALONG THE UPPER TX COAST/JUST OFFSHORE AND PWS
HOVERING AROUND 2 INCHES IN THIS AREA. GFS LOOKS OVERDONE WITH
QPF FORECAST (CONVECTIVE FEEDBACK)...SO FOLLOWED THE NAM SOLUTION
MORE CLOSELY. BOTTOM LINE IS WILL BE MAKING SOME SIGNIFICANT
CHANGES TO THE SHORT TERM PERIODS OF THE FORECAST AFTER ALL. HAVE
UPPED POPS ESPECIALLY SOUTHERN HALF OF SE TX. WILL ADD MENTION OF
HEAVY RAIN TO FORECAST HERE AND UPDATE HWOHGX TO INCLUDE WIDESPREAD
AMOUNTS OF 1 TO 2 INCHES...ISOLATED 3 TO 4 INCHES TO MATCH HPC
FORECAST.

SYSTEM WILL BE PULLING AWAY FROM THE AREA TUESDAY...MOVING WESTWARD
AROUND PERIPHERY OF UPPER HIGH INTO DEEP SOUTH TX. WILL KEEP 30 POPS
GOING FOR MOST OF THE AREA WITH ATMOSPHERE UNCAPPED AND PWS STILL IN
THE 1.7-1.8 INCH RANGE. BEYOND TUESDAY NIGHT...MADE VERY LITTLE CHANGE
TO THE FORECAST. EXPECT GENERALLY SEASONAL LATE JUNE CONDITIONS FOR
THE REST OF THE PERIOD WITH GRADUAL DAY TO DAY DRYING AS WEAK RIDGING
DEVELOPS ALOFT.

35

AVIATION...
BEGINNING TO SEE SOME SHOWER/THUNDERSTORM DEVELOPMENT AROUND AND TO
THE EAST OF THE TAF SITES. ADDITIONAL DEVELOPMENT IS POSSIBLE ALMOST
AREAWIDE AS THE AFTERNOON PROGRESSES...SO HAVE TEMPO TSRA MENTIONED
AT ALL BUT CLL. DIFFICULT TO TIME WHAT LOOKS LIKE COULD POSSIBLY BE
AN ACTIVE NIGHT AS SHOWERS/THUNDERSTORMS DEVELOP IN ASSOCIATION WITH
A CIRCULATION NOW CENTERED JUST TO THE NE OF CLL. WILL CALL FOR
PROB30 AFTER 06Z IN THE IAH-HOU-GLS CORRIDOR AND WILL INCLUDE LBX IN
THIS THINKING TOO. THANKS TO ZHU CWSU FOR EARLIER COORDINATION.  42

MARINE...
WILL HAVE CAUTION FLAGS OUT FOR ALL WATERS TONIGHT WITH SOUTH TO
SOUTHEAST WINDS EXPECTED TO BE GENERALLY IN A 15 TO 20 KNOT RANGE.
WINDS ARE EXPECTED TO RELAX TOMORROW AND BE IN A 10 TO 15 KNOT RANGE
FOR THE FIRST HALF OF THE WEEK AND DECREASE FURTHER TOWARD A 5 TO 10
KNOT RANGE TOWARD THE END OF THE WEEK.  42

HGX WATCHES/WARNINGS/ADVISORIES...
TX...FLOOD WATCH UNTIL 9 AM MONDAY FOR THE FOLLOWING ZONES: AUSTIN...
     BRAZORIA...CHAMBERS...COLORADO...FORT BEND...GALVESTON...
     HARRIS...JACKSON...LIBERTY...MATAGORDA...MONTGOMERY...
     POLK...SAN JACINTO...TRINITY...WALKER...WALLER...AND
     WHARTON.

GM...SMALL CRAFT SHOULD EXERCISE CAUTION UNTIL 4 AM MONDAY FOR THE
     FOLLOWING ZONES: GALVESTON BAY...MATAGORDA BAY...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...
     AND WATERS FROM HIGH ISLAND TO FREEPORT OUT 20 NM.

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...FLOOD WATCH UNTIL 9 AM MONDAY FOR THE FOLLOWING ZONES:
     BRAZORIA...CHAMBERS...FORT BEND...GALVESTON...HARRIS...
     LIBERTY...MATAGORDA...MONTGOMERY...POLK...SAN JACINTO...
     WALLER...AND WHARTON.

GM...NONE.
&&

HAZARDOUS WEATHER OUTLOOK...CORRECTED
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
310 PM CDT SUN JUN 18 2006

TXZ163-164-176>179-195>200-210>214-226-227-235>238-191200-
AUSTIN-BRAZORIA-BRAZOS-BURLESON-CHAMBERS-COLORADO-FORT BEND-
GALVESTON-GRIMES-HARRIS-HOUSTON-JACKSON-LIBERTY-MADISON-MATAGORDA-
MONTGOMERY-POLK-SAN JACINTO-TRINITY-WALKER-WALLER-WASHINGTON-
WHARTON-
310 PM CDT SUN JUN 18 2006

...LOCALLY HEAVY RAINFALL POSSIBLE ACROSS THE SOUTHERN HALF OF
SOUTHEAST TEXAS LATE TONIGHT AND MONDAY...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHEAST TEXAS.

.DAY ONE...TONIGHT
A MID TO UPPER LEVEL LOW PRESSURE SYSTEM WILL MOVE SLOWLY
SOUTHWARD ACROSS SOUTHEAST TEXAS TONIGHT. THIS SYSTEM WILL COMBINE
WITH A VERY MOIST AND UNSTABLE AIRMASS IN PLACE AND MAY RESULT IN
THE REDEVELOMENT OF THUNDERSTORMS...SOME WITH LOCALLY HEAVY
RAINFALL...LATER TONIGHT. THE PRIMARY HEAVY RAINFALL THREAT AREA
WILL BE SOUTH OF A LINE FROM COLUMBUS TO CONROE TO
CLEVELAND...ESPECIALLY CONCENTRATED OVER HARRIS...LIBERTY...
BRAZORIA...GALVESTON...AND CHAMBERS COUNTIES. IN THESE
AREAS...RAINFALL AMOUNTS OF 1/2 TO 1 INCH WILL BE POSSIBLE BY
EARLY MONDAY WITH LOCALLY HEAVIER AMOUNTS OF 2 TO 4 INCHES. MINOR
FLOODING OF STREETS...FEEDER ROADS...AND LOW WATER CROSSINGS WILL BE
POSSIBLE LATE TONIGHT. ELSEWHERE...CONSIDERABLY LOWER RAINFALL
AMOUNTS CAN BE EXPECTED.

.DAY TWO THROUGH SEVEN...MONDAY
THE MID TO UPPER LEVEL LOW PRESSURE SYSTEM WILL COMBINE WITH A
MOIST AND UNSTABLE AIRMASS IN PLACE TO PRODUCE SCATTERED SHOWERS
AND THUNDERSTORMS ACROSS SOUTHEAST TEXAS THROUGH THE DAY. SOME OF
THESE STORMS WILL PRODUCE LOCALLY HEAVY RAINFALL. THE PRIMARY HEAVY
RAINFALL THREAT AREA WILL BE SOUTH OF A LINE FROM COLUMBUS TO
CONROE TO CLEVELAND...ESPECIALLY CONCENTRATED OVER
HARRIS...LIBERTY... BRAZORIA...GALVESTON...AND CHAMBERS COUNTIES.
IN THESE AREAS...RAINFALL AMOUNTS OF 1 TO 2 INCHES CAN BE EXPECTED
THROUGH MONDAY EVENING WITH LOCALLY HEAVIER AMOUNTS OF 2 TO 4
INCHES. MINOR FLOODING OF STREETS...FEEDER ROADS...AND LOW WATER
CROSSINGS WILL BE POSSIBLE. ELSEWHERE...CONSIDERABLY LOWER RAINFALL
AMOUNTS CAN BE EXPECTED.

.DAYS THREE THROUGH SEVEN...TUESDAY THROUGH SATURDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS POSSIBLE LATE TONIGHT OR MONDAY.