Flash Flood Warning 37, NWS Houston/Galveston, TX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
340 PM CDT THU OCT 1 2009

.DISCUSSION...
WARM ADVECTION HAS RESULTED IN SHOWER DEVELOPMENT UNDER THE CAP
THIS AFTN. THE CONVECTION HAS BEEN TRAINING OVER THE OFFICE WHERE
RADAR ESTIMATES 1-2 INCHES OF RAIN HAS FALLEN. THIS ISOLATED
CONVECTION WILL PERSIST THROUGH THE EARLY EVENING HOURS. COLD
FRONT EXTENDS FROM SAN ANGELO TO MINERAL WELLS THIS HOUR. THE
FRONT IS EXPECTED TO REACH OUR NRN ZONES AROUND 1 AM THEN THE I-10
CORRIDOR JUST AFTER SUNRISE FRIDAY. 30 KT LOW LEVEL JET WILL
RESULT IN A CONTINUED INCREASE IN MOISTURE LEVELS THIS EVENING
WITH PWS REACHING AROUND 2 INCHES. NMM-WRF SOLUTION SHOWS A SOLID
LINE OF CONVECTION DEVELOPING ALONG THE FRONT AS THE CAP BREAKS
LATER THIS EVENING. GFS FORECASTS HELICITY VALUES OF >200 M2/S2
MAINLY OVER THE NRN ZONES FAVORING THE POTENTIAL FOR A FEW SEVERE
STORMS. THE PRIMARY SEVERE WEATHER THREAT WILL BE DAMAGING
STRAIGHT-LINE WINDS (GIVEN THE UNIDIRECTIONAL PROFILE). MARGINALLY
SEVERE HAIL ALSO POSSIBLE THOUGH THE FREEZING LEVELS ARE QUITE
HIGH. BAND OF CONVECTION WILL PERSIST OVER THE SRN HALF OF THE
AREA EARLY FRIDAY UNTIL THE FRONT STALLS JUST OFF THE COAST BY
LATE MORNING. CLEARING SKIES AND LOWER HUMIDITY LEVELS EXPECTED
FRI AFTN/EVENING IN THE WAKE OF THE FRONT AS PWS DROP TO BELOW AN
INCH MOST INLAND LOCATIONS.

SFC FRONT WILL BEGIN TO SLOWLY RETURN NORTH AS A WARM FRONT LATE
FRI NIGHT/SATURDAY AS A DEVELOPING TROUGH OVER THE WESTERN STATES
INDUCES A LOW LEVEL SOUTHERLY FLOW. 30-40 KT LOW LEVEL JET
DEVELOPS SATURDAY WHICH WILL RESULT IN A RAPID RETURN OF MOISTURE
TO THE AREA. PWS ARE FORECAST TO INCREASE TO 2.0-2.3 INCHES ACROSS
ALL OF SE TX BY 00Z SUNDAY. FLOW ALOFT BECOMES SOUTHWEST RESULTING
IN A SERIES OF WEAK UPPER LEVEL DISTURBANCES CROSSING THE AREA.
THESE DISTURBANCES WILL GENERATE LIFT WHILE THE SLOWLY RETREATING
WARM FRONT PROVIDES A FOCUS FOR CONVECTIVE DEVELOPMENT. HAVE
BLANKETED HIGH POPS (50S/60S) AREA WIDE SAT AFTN THROUGH SUNDAY.
THE PRIMARY THREATS WITH THE STORMS WILL BE HEAVY RAINFALL AND
CLOUD-TO-GROUND LIGHTNING. HPC QPF FCST HAS A BULLS-EYE OF 1.5-2.5
INCHES OF RAIN SATURDAY THROUGH SUNDAY ACROSS THE CWA...WITH
LOCALLY HIGHER AMOUNTS EXPECTED.

STRONG UPPER LOW WILL DIG SOUTH ACROSS NEVADA/CALIFORNIA EARLY
NEXT WEEK. IN RESPONSE TO THIS...STRONG UPPER RIDGING WILL DEVELOP
OVER THE GULF COAST REGION. MODELS FORECAST 500 MB HEIGHTS OF 591
DM OVER THE AREA BY TUESDAY/WEDNESDAY. COPIOUS AMOUNTS OF MOISTURE
WILL REMAIN IN PLACE OVER SE TX THROUGH MIDWEEK WITH PWS OF
1.8-2.1 INCHES. HOWEVER...SUBSIDENCE WILL INCREASE UNDER THE
STRENGTHENING RIDGE WHICH WILL RESULT IN LESS CONVECTIVE COVERAGE
ESPECIALLY NEAR THE COAST. WILL MAINTAIN CHANCE POPS MONDAY
THROUGH WEDNESDAY GIVEN THE ANTICIPATION OF SCATTERED CONVECTIVE
DEVELOPMENT. MODELS FORECAST VERY HIGH 1000-500 MB THICKNESS
VALUES (AROUND 580) AND HIGH SFC DEWPOINTS (75-80). TEMPS/HUMIDITY
WILL BE AT MID SUMMER LEVELS WITH MINS BARELY DROPPING BELOW 80
AND AFTN HEAT INDICES TOPPING OUT AROUND 105 DEGREES. LATEST
GFS/ENSEMBLE MEAN SHOW THE TROUGHING PHASING OVER THE PLAINS LATE
WEEK WITH STRONG FRONT PUSHING SLOWLY THROUGH THE AREA THU/FRI.
12Z ECMWF RUN ALSO BRINGS FRONT INTO THE AREA LATE WEEK BUT SHOWS
LIKELIHOOD OF IT STALLING AS TROUGHING PERSISTS OVER THE SOUTHWEST.

35

&&

.AVIATION...
SMALLISH CLUSTER OF STORMS THAT DEVELOPED OVER THE AREA AROUND THE
18Z TAF TIME IS STARTING TO SLOWLY MOVE OUT TO THE EAST THIS AFTN.
HOWEVER WE COULD STILL BE DEALING WITH CONVECTION IN THE AREA THIS
EVENING AS THAT LINE OF (NOW WEAKENING) SHRA CONTINUES TO PUSH EWD
FROM SC TX. THIS ALONG WITH THE PROGGED FROPA (AOA SUNRISE) SHOULD
KEEP AT LEAST VCSH/VCTS IN OVERNIGHT. OTHERWISE...WILL LIKELY KEEP
CIGS IN THE MVFR RANGE AND WINDS SLIGHTLY ELEVATED UNTIL THE FRONT
ARRIVES. VFR CONDITIONS TO PREVAIL IN THE POST-FRONTAL REGIME.  41

&&

.MARINE...
WHILE WINDS HAVE PICKED UP SOME THIS AFTERNOON...WE ARE STAYING BE-
LOW SCEC LEVELS. AND WITH WINDS JUST ABOVE THE SFC IN THE 15-20 KT
RANGE (AS PER HGX VWP) THIS TREND SHOULD CONTINUE AT LEAST FOR THE
SHORT TERM. FOR TOMORROW STILL LOOKING FOR A WEAK COLD FRONT TO AP-
PROACH THE COASTAL WATERS AND THEN STALL. THIS BOUNDARY PROGGED TO
RETREAT NORTH ON SATURDAY WITH MODERATE TO STRONG ONSHORE WINDS RE-
DEVELOPING BY SATURDAY NIGHT/SUNDAY. THE PERSISTENT SOUTHERLY FLOW
(ALONG WITH A SERIES OF UPPER LEVEL DISTURBANCES) EXPECTED TO PREV-
AIL THROUGH THE FIRST PART OF NEXT WEEK.  41

&&

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      66  85  62  78  69 /  70  10  10  60  60
HOUSTON (IAH)              72  84  65  83  71 /  70  40  20  60  60
GALVESTON (GLS)            76  84  75  82  76 /  40  50  20  60  50

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...NONE.
&&

DISCUSSION...35
AVIATION/MARINE...41

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
350 PM CDT THU OCT 1 2009

TXZ163-164-176>179-195>200-210>213-021200-
AUSTIN-BRAZOS-BURLESON-COLORADO-GRIMES-HARRIS-HOUSTON-LIBERTY-
MADISON-MONTGOMERY-POLK-SAN JACINTO-TRINITY-WALKER-WALLER-
WASHINGTON-
350 PM CDT THU OCT 1 2009

...SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS EVENING AND
OVERNIGHT...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHEAST TEXAS.

.DAY ONE...TONIGHT

A COLD FRONT WILL APPROACH SOUTHEAST TEXAS THIS EVENING AND MOVE
SLOWLY THROUGH THE AREA DURING THE OVERNIGHT HOURS. THE FRONT
WILL COMBINE WITH DEEP TROPICAL MOISTURE TO GENERATE A BAND OF
SHOWERS AND THUNDERSTORMS. THESE STORMS ARE EXPECTED TO BEGIN
AFFECTING THE NORTHERN PORTIONS OF SOUTHEAST TEXAS AFTER 10
PM...REACHING THE INTERSTATE 10 CORRIDOR LATE TONIGHT. MODERATE
SHEAR IN THE ATMOSPHERE WILL SUPPORT THE POTENTIAL FOR A FEW
SEVERE STORMS NORTH OF THE I-10 CORRIDOR. THE MAIN THREAT AREA FOR
SEVERE WEATHER WILL BE NORTH OF A LINE FROM COLUMBUS TO HOUSTON TO
CLEVELAND. THE MAIN TIME FRAME WILL BE 10 PM THIS EVENING TO 5 AM
FRIDAY. THE PRIMARY SEVERE WEATHER THREATS WILL BE DAMAGING
STRAIGHT-LINE WINDS AND MARGINALLY SEVERE HAIL.

.DAYS TWO THROUGH FOUR...FRIDAY THROUGH SUNDAY

AFTER A BREAK ON FRIDAY...THUNDERSTORM ACTIVITY IS EXPECTED TO
CONTINUE OVER THE WEEKEND AS THE FRONT STALLS ALONG THE UPPER
TEXAS COAST. THE THUNDERSTORM ACTIVITY SHOULD REMAIN BELOW SEVERE
LIMITS BUT WITH ABUNDANT LOW LEVEL MOISTURE IN PLACE...HEAVY
RAINFALL WILL BE POSSIBLE OVER THE WEEKEND. MOST AREAS WILL LIKELY
RECEIVE 1 TO 2 INCHES OF RAINFALL BUT LOCALIZED AMOUNTS CLOSER TO
2 TO 4 INCHES MAY BE POSSIBLE WITH STRONGER STORMS THAT TRAIN
ACROSS THE SAME AREA.

.DAYS FIVE THROUGH SEVEN...MONDAY THROUGH WEDNESDAY

HAZARDOUS WEATHER IS NOT EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED TONIGHT.

TXZ214-226-227-235>238-021200-
BRAZORIA-CHAMBERS-FORT BEND-GALVESTON-JACKSON-MATAGORDA-WHARTON-
350 PM CDT THU OCT 1 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHEAST TEXAS.

.DAY ONE...TONIGHT

A COLD FRONT AND AN ASSOCIATED BAND OF SHOWERS AND THUNDERSTORMS
WILL REACH THE AREA LATE TONIGHT. THE STRONGEST STORMS WILL BE
CAPABLE OF PRODUCING GUSTY WINDS...DANGEROUS LIGHTNING...AND BRIEF
HEAVY RAINFALL.

.DAYS TWO THROUGH FOUR...FRIDAY THROUGH SUNDAY

THUNDERSTORMS WILL COME TO AN END FRIDAY MORNING. AFTER A BREAK ON
FRIDAY...THUNDERSTORM ACTIVITY IS EXPECTED TO CONTINUE OVER THE
WEEKEND AS THE FRONT STALLS ALONG THE UPPER TEXAS COAST. THE
THUNDERSTORM ACTIVITY SHOULD REMAIN BELOW SEVERE LIMITS BUT WITH
ABUNDANT LOW LEVEL MOISTURE IN PLACE...HEAVY RAINFALL WILL BE
POSSIBLE OVER THE WEEKEND. MOST AREAS WILL LIKELY RECEIVE 1 TO 2
INCHES OF RAINFALL BUT LOCALIZED AMOUNTS CLOSER TO 2 TO 4 INCHES
MAY BE POSSIBLE WITH STRONGER STORMS THAT TRAIN ACROSS THE SAME
AREA.

.DAYS FIVE THROUGH SEVEN...MONDAY THROUGH WEDNESDAY

HAZARDOUS WEATHER IS NOT EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED.

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