Flash Flood Warning 31, NWS Houston/Galveston, TX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
930 PM CDT WED JUL 4 2007

...DANGEROUS HEAVY RAIN EVENT DEVELOPING FOR SOUTHEAST TEXAS...

.UPDATE...
WILL RAISE POPS AONG THE COAST AS MOISTURE AXIS LIES ALONG THE
COAST AND THERE IS SPEED AND DIRECTIONAL CONVERGENCE SERVING AS AN
ADDITIONAL FOCUS FOR RAIN. MOISTURE FETCH EXTENDS FROM BAY CITY TO
EAST OF CORPUS CHRISTI. AN EXTENDED PERIOD OF TRAINING RAIN IS
EXPECTED. WILL FRESHEN THE FLOOD WATCH AND PROBABLY INCREASE RAIN
AMOUNTS OVERNIGHT. 43

&&

.DISCUSSION...

&&

.PREV DISCUSSION... /ISSUED 846 PM CDT WED JUL 4 2007/

AVIATION...
A BREAK IN THE RAINFALL ACTIVITY EXISTS OVER THE TERMINAL SITES AT
THIS HOUR. HOWEVER...THE RAINFALL POTENTIAL REMAINS HIGH AND KEPT
THE MENTION OF SHOWERS OR THUNDERSTORMS IN THE FORECASTS THROUGH
THE TAF PERIOD. A WEAK WARM FRONT APPEARED TO BE FORMING OVER THE
COASTAL PLAIN EARLIER THIS EVENING AND SOME MVFR CEILINGS WERE
DEVELOPING.

THE CONFIDENCE LEVEL WAS ABOUT A 3 ON A SCALE OF 1 TO 5 FOR THE
FORECAST PAST 06Z TONIGHT GIVEN THE RECENT HISTORY OF THE MODELS.
THE MOS GUIDANCE AND NAM12 TIME SECTIONS DIFFER SOMEWHAT IN THE
FORMATION OF THE LOW CEILINGS ALTHOUGH BOTH INDICATE MVFR
SCATTERED TO BROKEN CEILINGS. FIGURED THAT THESE WILL DEVELOP BY
06Z OVER ALL THE TERMINAL SITES. THE MODELS INDICATED BETTER
RAINFALL POTENTIAL AT THE COASTAL SITES THURSDAY THAN FURTHER
INLAND ALTHOUGH THE GFS WAS MORE TO THE SOUTH OF THE TERMINAL
SITES AT 12Z. BY 18Z THE GFS HAD THE BEST RAINFALL TO THE WEST
TOWARD THE HILL COUNTRY. WENT WITH VCTS ALL DAY OVER THE INLAND
SITES AND A TSRA MENTION BETWEEN 12Z AND 18Z AT GLS AND LBX.

40

PREV DISCUSSION... /ISSUED 824 PM CDT WED JUL 4 2007/

DISCUSSION...
ONCE AGAIN...THE THREAT FOR HEAVY RAIN EXISTS. 00Z SOUNDING DATA
SHOWS PW VALUES BETWEEN 2.20 AND 2.30 INCHES. 850-500 LAYER SHOWS
LOW PRESSURE NORTH OF VCT. RADAR RETURNS ALSO SHOW THE CYCLONIC
TURNING. 00Z SURFACE ANALYSIS SHOWS A WEAK AREA OF LOW PRESSURE
NORTH OF BRO AND A WEAK SURFACE TROUGH OF LOW PRESSURE FROM VCT TO
CLL. SATELLITE DERIVED WIND PLOTS SHOWS SE TX IN A BROADLY
DIVERGENT UPPER WIND PATTERN. CURRENT THINKING IS THAT ANOTHER
MCS WILL FORM TONIGHT AND FOCUS CLOSE TO THE 850-500 CIRCULATION
AND ALSO ALONG THE WEAK LOW PRESSURE TROUGH FROM CLL TO EDNA. WILL
LEAVE FFA AS CURRENTLY CONFIGURED BUT WILL PROBABLY RAISE POPS
WEST OVERNIGHT. THINK POPS OUT EAST CAN BE LOWERED BUT WILL AWAIT
NEW MODEL GUIDANCE BEFORE MAKING ANY OTHER CHANGES. PERSONS LIVING
ALONG WATERSHEDS AND RIVERS IN JACKSON...MATAGORDA...COLORADO AND
WHARTON COUNTIES SHOULD REMAIN DILIGENT OVERNIGHT. 43

&&

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      73  85  74  88  74 /  80  70  50  50  30
HOUSTON (IAH)              74  85  75  88  75 /  60  70  50  40  20
GALVESTON (GLS)            76  85  78  87  79 /  60  60  50  40  20

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...FLASH FLOOD WATCH THROUGH THURSDAY AFTERNOON FOR THE FOLLOWING
     ZONES: 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.

GM...SMALL CRAFT SHOULD EXERCISE CAUTION UNTIL 5 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.

&&

DISCUSSION...43

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
248 PM CDT WED JUL 4 2007

GMZ330-335-TXZ163-164-176>179-195>200-210>214-226-227-235>238-
052000-
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-WHARTON-
248 PM CDT WED JUL 4 2007

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHEAST TEXAS.

.DAY ONE...THIS AFTERNOON AND TONIGHT

AN UPPER LEVEL LOW ACROSS CENTRAL TEXAS AND ABUNDANT TROPICAL
MOISTURE ACROSS THE AREA WILL PRODUCE SCATTERED TO NUMEROUS
SHOWERS AND THUNDERSTORMS...WITH SOME STORMS PRODUCING LOCALLY
HEAVY RAINFALL...ACROSS SOUTHEAST TEXAS TONIGHT INTO THURSDAY.

A FLASH FLOOD WATCH IS IN EFFECT THROUGH THURSDAY AFTERNOON FOR
SOUTHEAST TEXAS. WIDESPREAD RAINFALL AMOUNTS OF 2 TO 4
INCHES...WITH ISOLATED TOTALS OF 4 TO 6 INCHES CAN BE EXPECTED
OVER THE WATCH AREA THROUGH THURSDAY. A FLASH FLOOD WATCH MEANS
THAT RAPIDLY RISING WATER OR FLOODING ARE POSSIBLE OVER THE WATCH
AREA. PERSONS IN THE WATCH AREA SHOULD CHECK PREPAREDNESS
REQUIREMENTS...KEEP INFORMED...AND BE READY FOR QUICK ACTION IF
FLASH FLOODING IS OBSERVED OR A WARNING IS ISSUED.

.DAY TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

ABUNDANT TROPICAL MOISTURE ACROSS SOUTHEAST TEXAS WILL CONTINUE
TO PRODUCE SCATTERED SHOWERS AND THUNDERSTORMS THURSDAY AS THE
UPPER LEVEL LOW MEANDERS ACROSS TEXAS. HEAVY RAINFALL WILL STILL
BE POSSIBLE ON THURSDAY AND THE FLASH FLOOD WATCH HAS BEEN
EXTENDED THROUGH THURSDAY AFTERNOON FOR SOUTHEAST TEXAS. RAIN
CHANCES SHOULD DIMINISH TOWARDS THE WEEKEND AS THE UPPER LOW IS
EXPECTED TO WEAKEN.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY NOT BE NEEDED.