Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 171607
AFDHGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1107 AM CDT WED SEP 17 2014

.UPDATE...
AFTER MORNING COLLABORATION WITH WPC...THERE HAS BEEN AN ONGOING
ADJUSTMENT OF OUR POPS/WX/QPF GRIDS. THE MAIN THEME IS FOR THE
THREAT OF MORE AREA-WIDE HEAVY RAINFALL LEADING TO FLOODING. THE
CLUSTERS THAT HAVE PASSED ACROSS NORTH-NORTHWEST HARRIS COUNTY HAVE
DROPPED LARGE AMOUNTS OF RAIN IN A SHORT AMOUNT OF TIME...WITH AN
EXAMPLE OF AN INCH WITHIN 15 MINUTES AT THE CYPRESS CREEK AT FM
249 HCFCD RAIN GAUGE. CLUSTERS OF SLOW-MOVING SHOWERS AND STORMS
FORMING WITHIN A HIGHLY MOIST TROPICAL-IN-NATURE AIR MASS HAVE THE
POTENTIAL OF PUTTING DOWN HIGH RAINFALL AMOUNTS/RATES OVER THE
NEXT 24 TO 36 HOURS. FFG HAS HOURLY RATES OF TWO TO THREE INCHES
LEADING TO FLOODING CONCERNS...THREE TO FOUR INCH AMOUNTS OVER 3
TO 6 HOURS WILL SIGNIFICANTLY HEIGHTEN THE FLOOD THREAT...AS WELL.
IN GENERAL...RECENT HIGH RAINFALL RATES/HIGHER RELATIVE-VOLUMETRIC
SOIL CONTENT VALUES RESIDE OVER THOSE COUNTIES EAST AND SOUTHWEST
OF THE CITY SO...ALONG WITH HOUSTON METRO/SUBURBS...THESE WILL BE
THE AREAS THAT WILL MOST LIKELY EXPERIENCE FLOODING ISSUES. POINTS
SURROUNDING THESE LOCATIONS CAN HANDLE MORE RAINFALL...BUT WITH
THESE RECENTLY HIGH HOURLY RAINFALL RATES OF BETWEEN A HALF OF AN
INCH TO NEAR NEAR TWO INCHES...ANY COMMUNITY COULD BE IN THE HAT
IN DEALING WITH (FLASH) FLOODING. THE REST OF THE FORECAST WILL
REMAIN UNCHANGED...OVERCAST WITH AFTERNOON TEMPERATURE EXTREMA IN
THE MID TO UPPER 80S WITH MORNING READINGS FALLING INTO THE MIDDLE
70S. 31

&&

.PREV DISCUSSION... /ISSUED 446 AM CDT WED SEP 17 2014/

DISCUSSION...
NOT A LOT OF CHANGES WITH THE GOING FCST OF CONTINUED RAINS FOR
TODAY/TOMORROW. VERY HIGH PW`S NOTED OVER THE REGION (~2.3") AND
NOT EXPECTING THAT WE WILL NEED A LOT OF HEATING FOR PCPN
DEVELOPMENT TO START AGAIN LATER THIS MORNING/AFTN. AS THIS
MOISTURE LINGERS INTO TOMORROW WE MAY HAVE THE REMNANTS OF ODILE
TO DEAL WITH AS WELL. WILL LIKELY KEEP WITH AVG RAINFALL TOTALS
FROM .5 TO 1`... ISO 3-4" TODAY THROUGH TONIGHT.

RAIN CHANCES TO DECREASE SOME BY FRI (ON INTO THE WEEKEND) WITH
WEAK UPPER RIDGING BUILDING IN BEHIND THE UPPER TROF (ODILE REMNANTS).
HOWEVER WILL BE KEEPING ISO/SCT POPS IN FOR THIS PERIOD AS THE DEEP
TROPICAL MOISTURE LINGERS OVER THE AREA. LONG RANGE MODELS KEEPING
WITH THE PASSAGE OF THE COLD FRONT AOA MON...BUT WITH VARYING DEGREES
OF STRENGTH. ECMWF KEEPING ITS FROPA A BIT MORE ROBUST THAN GFS ATTM...
BUT GIVEN THE MORE CONSISTENT PROGS OF A FAIRLY DEEP N/NWLY FLOW
ALOFT WILL BE LEANING MORE TOWARDS THE ECMWF FOR THIS TIME FRAME.
41

&&

MARINE...
A FEW SHOWERS AROUND GALVESTON BAY MOVING SOUTHEAST AND A FEW
SHOWERS DEVELOPING AROUND MATAGORDA BAY AND MOVING NORTH. WEAK MID
LEVEL RIDGING OVER THE WESTERN GULF APPEARS TO BE DICTATING MOTION
FOR NOW BUT AS THE RIDGING MOVES WEST EXPECT THAT WEAK UPPER LEVEL
DISTURBANCES WILL TRACK FROM NW TO SE THROUGH SETX AND INTO THE
COASTAL WATERS COMBINING WITH DAYTIME HEATING TO INCREASE COVERAGE.
LIGHT WINDS TYPICALLY IN THE 7-12 KNOT RANGE WILL PREVAIL FROM THE
SOUTH. MAY HAVE A CLUSTER TO DEAL WITH OVER THE COASTAL WATERS
TOMORROW MORNING AS NW FLOW ALOFT INTERACTS WITH PUSH OF DRIER AIR
INTO LA AND MOIST AXIS LINES UP BENEATH THE TRACK OF THE DISTURBANCES
COMING IN NW. AM FAVORING THE ECMWF FOR THE FRONTAL BOUNDARY
ARRIVING LATE MONDAY/TUESDAY. 45

&&

AVIATION...
MESSY WX ACROSS THE REGION. LINE OF LOW CLOUDS IFR/VLIFR FROM
6R3- CXO-11R WITH HIGH CLOUDS SOUTH OF THE LINE. SOME DEVELOPMENT
SOUTHWARD SEEMS POSSIBLE BUT CONFIDENCE IS LOW SO FOR NOW WILL
KEEP IAH VFR. SHOWERS SHOULD DEVELOP AS TEMPERATURES RISE INTO THE
LOWER 80S ACROSS THE SOUTHERN TERMINALS THEN EXPAND NORTHWARD
THROUGH THE AFTERNOON. SLOW MOVING STORMS WILL POSE A THREAT OF
HEAVY DOWNPOURS BUT IS HARD TO TELL IF ONE OF THE AIRPORTS IS
FAVORED FOR GETTING WHACKED. FOR NOW WILL JUST KEEP A TEMPO GOING
FOR ROUGHLY 17-21Z BUT NEEDLESS TO SAY IFR VISBY MAY DEVELOP WITH
HEAVY DOWNPOURS. STORMS MAY BE SLOWER TO DEPART THAN THEY DID THIS
EVENING AND MOST MODELS KEEP IT ACTIVE THROUGH 01-03Z THURSDAY.
45

&&

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      89  75  86  72  90 /  70  60  70  20  40
HOUSTON (IAH)              88  75  86  73  89 /  80  40  80  30  50
GALVESTON (GLS)            86  79  84  78  87 /  60  60  70  40  50

&&

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

$$

DISCUSSION...31/43


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