Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 260944
AFDHGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
444 AM CDT TUE AUG 26 2014

.DISCUSSION...
MORNING SFC ANALYSIS SHOWS FAIRLY WEAK PRESSURE GRADIENT ACROSS
MUCH OF TX WITH MAINLY E/SE WINDS ALONG THE UPPER TX COAST. WATER
VAPOR IMAGERY SHOWS A SHORT WAVE TROUGH MOVING ACROSS THE N GULF
TOWARDS SE TX. THE 00Z SOUNDING FROM LCH SHOWED 2.4 INCHES OF
PRECIP WATER WHICH IS QUITE HIGH FOR THIS TIME OF YEAR BEING 2 STD
DEV FROM NORMAL. GOES PRECIP WATER SOUNDER DATA SHOWS AT LEAST
THIS MUCH MOISTURE OVER A LARGE PORTION OF THE AREA. THIS BROAD
AREA OF DEEP MOISTURE EXTENDS FROM INLAND AREAS TO WELL OFF THE
COAST. SHORT RANGE MODELS ADVECT MUCH MORE MOIST AIRMASS INTO SE
TX WHICH MAKES SENSE BASED OFF 00Z LCH WIND PROFILE. THE NAM SEEMS
TO BE A BIT MORE AGGRESSIVE WITH BRINGING THE MOISTURE INTO THE
AREA WHERE GFS IS SLOWER. GFS IS ALSO FASTER IN BRINGING SOME
DRIER AIR INTO THE AREA FROM THE EAST. THIS MAY IMPACT
THUNDERSTORM CHANCES MID WEEK ESPECIALLY OVER NORTHERN PORTIONS OF
SE TX. FOR NOW RADAR SHOWS ACTIVITY ORGANIZING IN THE GULF AND
THIS WILL LIKELY BE THE BEGINNING OF THUNDERSTORM ACTIVITY ALONG
THE COAST. THINK 40/50 POPS LOOK ON TRACK FOR MUCH OF THE AREA FOR
THE REST OF THE WEEK. ON A CURIOUS NOTE...MESO MODELS SUCH AS WRF
ARW AND HRRR ARE NOT VERY ROBUST WITH CONVECTION FORMING UNTIL
MUCH LATER IN THE AFTERNOON. THIS BRINGS IN SOME DOUBT AS TO HOW
CONVECTION WILL EVOLVE TODAY.

UPPER LEVEL PATTERN WILL BE QUITE CONDUCIVE FOR CONVECTION. WATER
VAPOR IMAGERY SHOWS SHORTWAVE MOVING INTO SE TX FROM THE N GULF
TODAY AND FORECAST MODELS CONTINUE TO STALL THIS FEATURE ALONG THE
COAST OR JUST INLAND OF MIDDLE TX COAST ON WEDNESDAY. THIS MEANS
AN OVERALL WEAKNESS IN THE RIDGE WILL EXIST AND ONLY STRENGTHENED
BY BROAD TROUGH NOW OVER THE GREAT BASIN MOVING INTO THE PLAINS
FOR FRIDAY INTO SATURDAY. THE CUTOFF SHORTWAVE OR TUTT LOW WILL
THEN LIFT NORTH AS THE UPPER TROUGH STARTS TO MOVE THROUGH THE
PLAINS LATE FRI INTO SAT. AFTER THE TROUGH LIFTS OVERALL UPPER
LEVEL RIDGING OCCURS BUT THE RIDGE SEEMS TO BE STRETCHED OUT ALL
ALONG THE SOUTHERN TIER OF STATES.

THE OTHER MAJOR INGREDIENT FOR THUNDERSTORM CHANCES IS MOISTURE.
GOES SOUNDER PRECIP WATER PRODUCT SHOWS DEEP MOISTURE AXIS OR
ATMOSPHERIC MOISTURE RIVER COMING FROM THE CARIBBEAN INTO THE N
GULF. THIS PLUME OF MOISTURE WILL VARY IN ITS OVER CONTENT FROM
DAY TO DAY BUT IT WILL NOT TAKE MUCH TIME FOR CONVECTION TO
DEVELOP. MODEL SOUNDINGS SUPPORT CONVECTIVE TEMPS IN THE UPPER 80S
TO LOW 90S WITH PRECIP WATER VALUES AROUND 2.2 TO 2.4 INCHES. THIS
MOISTURE PLUME REMAINING IN PLACE FOR THE NEXT DAY OR TWO SHOULD
SUPPORT CONTINUED THUNDERSTORM ACTIVITY ACROSS THE AREA.
CONVECTIVE TEMPS LOOK TO BE IN THE UPPER 80S TO LOW 90S. WITH
BREAKS IN CLOUD COVER THESE TEMPS LOOK TO BE ACHIEVABLE EVEN IN
THE LATE MORNING HOURS. IT LOOKS LIKE TODAY INTO WEDNESDAY WILL
CARRY THE HIGHEST CHANCES BUT EVEN 30/40 POPS LOOK REASONABLE FOR
THE END OF THE WEEK.

CONVECTION AND CLOUD COVER SHOULD KNOCK TEMPS DOWN A COUPLE OF
DEGREES FROM THE LAST FEW DAYS. HIGH TEMPS WILL REACH LOW 90S
ALONG THE COAST AND POSSIBLY INLAND. MIN TEMPS MAY BE ABOVE
NORMAL WITH HIGHER MOISTURE ALONG THE COAST. LOW TEMPS WILL MAINLY
BE DRIVEN BY ANY OUTFLOW BOUNDARIES THAT MOVE THROUGH THE AREA.

MAIN IMPACTS FROM THIS CHANGE IN THE WEATHER PATTERN WILL BE
POSSIBILITY OF HEAVY RAINFALL ON ANY OF THE NEXT FEW DAYS. HIGHEST
RAINFALL TOTALS WILL LIKELY BE ALONG THE COAST AND OFFSHORE.
THAT`S NOT TO SAY A FEW STRONG STORMS COULD NOT FORM INLAND WHICH
COULD PRODUCE HEAVY RAINFALL. HOURLY RAIN RATES OF 1-2 INCHES AN
HOUR WOULD NOT BE OUT OF THE QUESTION SO ISO 1-3 INCH AMOUNTS
WOULD BE POSSIBLE. LOOKING AT GRIDDED FFG AND NASA SPORT LIS
DATA...IF ANYTHING MOST FLOOD PRONE AREAS WILL BE EAST OF
INTERSTATE 45 INTO E TX. AT THIS TIME ANY FLOODING PROBLEMS WILL
BE VERY LOCALIZED. OF COURSE URBAN AREAS WITH POOR DRAINAGE WILL
ALWAYS BE AN ISSUE ONCE RAIN RATES APPROACH 2 INCHES AN HOUR. THE
HARDEST PART OF THE FORECAST IS TRYING THE NARROW DOWN ANY ONE DAY
THAT WILL HAVE A HIGHER POTENTIAL FOR HEAVY RAINFALL. AT THIS TIME
THE NEXT 4 DAYS HAVE THAT POTENTIAL.

39


&&

.MARINE...
AN UPPER LEVEL DISTURBANCE WILL BRING SHOWERS AND THUNDERSTORMS
TO THE WATERS TODAY AND WEDNESDAY. FAIRLY LIGHT EAST TO SOUTHEAST
FLOW WILL BECOME MORE MODERATE...MAINLY IN THE 10 TO 15 KNOT
RANGE...LATER THIS AFTERNOON...AND CONTINUING THROUGH LATE IN THE
WEEK. THERE WILL BE AN INCREASE IN SEAS CORRESPONDING...INTO THE 2
TO 4 FEET RANGE FOR COASTAL WATERS.

46

&&

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      96  76  96  75  93 /  20  20  20  20  30
HOUSTON (IAH)              92  77  93  76  92 /  50  20  40  20  50
GALVESTON (GLS)            90  80  88  80  89 /  50  40  50  50  50

&&

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

$$

DISCUSSION...39
AVIATION/MARINE...46


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