Flash Flood Warning 38, NWS Houston/Galveston, TX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1050 PM CDT SAT SEP 23 2006

.UPDATE...
OUTFLOW BOUNDARY AND BAND OF CONVECTION HAS PUSHED SOUTH TO ALONG I-
10. WILL DROP THE FLOOD WATCH AND LOWER POPS FOR THE NRN HALF OF SE
TX. COLD FRONT REMAINS NORTH OF THE CWA AND ADDITIONAL DEVELOPMENT
COULD OCCUR ALONG THE FRONT...BUT NOT ENOUGH TO CREATE ANY PROBLEMS.
WILL ALSO TRIM RAINFALL AMOUNTS WITH THE REMAINING WATCH...ALTHOUGH
TRAINING OF ECHOES IS LIKELY TO OCCUR SOUTH OF I-10.

35

&&

.PREV DISCUSSION... (ISSUED 815 PM CDT SAT SEP 23 2006)

DISCUSSION...
A BAND OF THUNDERSTORMS WITH VERY HEAVY RAINFALL ONGOING ALONG THE
PREFRONTAL TROUGH FROM BRENHAM TO JUST SOUTH OF HUNTSVILLE TO NEAR
LIVINGSTON. THIS BAND IS PUSHING SOUTHEAST AT AROUND 15 MPH. TRAINING
OF STORMS HAS BEEN OCCURRING PARTICULARLY ON THE EASTERN PART OF THE
LINE OVER WALKER AND POLK COUNTIES. RADAR INDICATES THAT A LARGE
PORTION OF POLK AND WALKER COUNTIES HAVE BEEN AVERAGING 2-3 IN/HOUR
RAINFALL RATES WITH ISOLATED TOTALS OF 6 TO 8 INCHES OVER POLK
COUNTY. 00Z ANALYSIS SHOWS COPIOUS AMOUNTS OF MOISTURE IN PLACE ACROSS
SE TX THIS EVENING WITH SFC DEWPOINTS IN THE MID TO UPPER 70S...PWS
AROUND 2.3 INCHES AND 850 MB DEWPOINTS OF 18-20C. DEEP MOISTURE WILL
REMAIN IN PLACE DUE TO A PERSISTENT 20-30 KNOT LOW LEVEL JET. IN
ADDITION...RATHER STRONG DIFFLUENCE NOTED AT THE 300 MB LEVEL. AS THE
PREFRONTAL TROUGH CONTINUES PUSHING SOUTHEAST INTO OUR CENTRAL/COASTAL
ZONES...THESE FACTORS WILL COMBINE TO KEEP THUNDERSTORMS WITH HEAVY
RAINFALL ACTIVE ALONG THE BOUNDARY. HAVE DECIDED TO GO WITH A FLOOD
WATCH FOR ALL BUT THE FAR NORTHERN TIER OF COUNTIES UNTIL 10Z.
EXPECTING WIDESPREAD RAINFALL AMOUNTS OF 1 TO 3 INCHES WITH ISOLATED
TOTALS OF 5 TO 10 INCHES POSSIBLE. HAVE UPDATED WX/POPS IN FORECAST
FOR THE REST OF THE NIGHT. ANTICIPATE ADDITIONAL UPDATES AS THE AREA
OF CONVECTION PUSHES SOUTHEAST.

AS THIS APPEARS TO BE EVOLVING INTO MORE OF A HEAVY RAIN VS. SEVERE
WEATHER THREAT WILL DROP THE MENTION OF SEVERE IN THE FORECAST.
HOWEVER...ISOLATED PULSE TYPE SEVERE STORMS WILL REMAIN POSSIBLE...SO
WILL KEEP MENTION IN HWOHGX.

35

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...FLOOD WATCH UNTIL 5 AM SUNDAY FOR THE FOLLOWING ZONES: AUSTIN...
     BRAZORIA...CHAMBERS...COLORADO...FORT BEND...GALVESTON...
     HARRIS...JACKSON...LIBERTY...MATAGORDA...WALLER...AND
     WHARTON.

GM...SMALL CRAFT SHOULD EXERCISE CAUTION UNTIL 1 AM SUNDAY FOR THE
     FOLLOWING ZONES: GALVESTON BAY...MATAGORDA BAY...WATERS
     FROM FREEPORT TO THE MATAGORDA SHIP CHANNEL OUT 20 NM...AND
     WATERS FROM HIGH ISLAND TO FREEPORT OUT 20 NM.

     SMALL CRAFT ADVISORY UNTIL 1 AM SUNDAY FOR THE FOLLOWING ZONES:
     WATERS FROM FREEPORT TO THE MATAGORDA SHIP CHANNEL 20 NM TO
     60 NM...AND WATERS FROM HIGH ISLAND TO FREEPORT 20 TO 60
     NM.

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1057 PM CDT SAT SEP 23 2006

TXZ163-164-176>179-195>200-210>214-226-227-235>238-241200-
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-
1057 PM CDT SAT SEP 23 2006

...FLOOD WATCH REMAINS IN EFFECT FOR THE SOUTHERN HALF OF
SOUTHEAST TEXAS UNTIL 5 AM SUNDAY...

...LOCALLY HEAVY RAINFALL LIKELY ACROSS THE SOUTHERN HALF OF
SOUTHEAST TEXAS TONIGHT...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHEAST TEXAS.

.DAY ONE...TONIGHT

NUMEROUS SHOWERS AND THUNDERSTORMS ARE ONGOING ACROSS THE SOUTHERN
HALF OF SOUTHEAST TEXAS AS A WEAK OUTFLOW BOUNDARY INTERACTS WITH
DEEP MOISTURE IN PLACE. THUNDERSTORMS ARE EXPECTED TO PERSIST OVER
THIS AREA FOR THE NEXT FEW HOURS.

LOCALLY HEAVY RAINFALL IS LIKELY ACROSS ALL OF SOUTHEAST TEXAS
TONIGHT. RAINFALL AMOUNTS WILL AVERAGE 1 TO 2 INCHES WITH ISOLATED
TOTALS OF 3 TO 7 INCHES POSSIBLE WHERE STORMS REPEATEDLY TRAIN
OVER THE SAME AREAS. THIS HEAVY RAINFALL WILL HAVE THE POTENTIAL
TO CAUSE SIGNIFICANT FLOODING OF STREETS...FEEDER ROADS...LOW
WATER CROSSINGS...AND OTHER ROADWAYS TONIGHT.

BE ESPECIALLY CAUTIOUS AT NIGHT WHEN IT IS HARDER TO RECOGNIZE THE
DANGERS OF FLOODS AND FLASH FLOODS. IF FLASH FLOODING IS
OBSERVED...ACT QUICKLY. MOVE UP TO ESCAPE FLOOD WATERS. DO NOT
STAY IN AREAS SUBJECT TO FLOODING WHEN WATER BEGINS RISING.

YOU SHOULD MONITOR LATER FORECASTS AND BE ALERT FOR POSSIBLE FLOOD
WARNINGS. THOSE LIVING IN AREAS PRONE TO FLOODING SHOULD BE
PREPARED TO TAKE ACTION SHOULD FLOODING DEVELOP.

.DAY TWO...SUNDAY
NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS THREE THROUGH SEVEN...MONDAY THROUGH FRIDAY
NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...
SPOTTER ACTIVATION IS POSSIBLE THIS EVENING.