Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 231034
AFDHGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
534 AM CDT SAT MAY 23 2015

.SHORT TERM...
TODAY THROUGH SUNDAY.

...A FLASH FLOOD WATCH IS IN EFFECT FOR SOUTHEAST TEXAS THIS EVENING
THROUGH MONDAY EVENING...

A RELATIVELY QUIET START TO MEMORIAL DAY WEEKEND FOR THE REGION WILL
QUICKLY GIVE WAY TO A STORMY END... WITH SEVERE WEATHER... RIVER AND
FLASH FLOODING... AND HAZARDOUS MARINE CONDITIONS EXPECTED OVER THE
NEXT 36 HOURS. EARLY MORNING WATER VAPOR IMAGERY SHOWED AN UPPER LOW
CHURNING OVER SOUTHERN NEVADA WITH A SHORTWAVE TROUGH ROTATING
AROUND THIS FEATURE INTO WEST CENTRAL TEXAS... WITH ANOTHER
SHORTWAVE TROUGH LOCATED FARTHER UPSTREAM NEAR THE WASHINGTON/OREGON
BORDER. 06Z SURFACE ANALYSIS DEPICTING WARM AND MOIST AIR PUSHING
BACK INTO THE REGION /DEW POINTS IN THE LOW TO MID 70S/ BEHIND A
WARM FRONT STRETCHING FROM NORTH OF MIDLAND TO NEAR THE D/FW
METROPLEX SOUTHEAST TOWARDS THE SABINE PASS. A DEVELOPING SURFACE
TROUGH WAS NOTED EXTENDING FROM SOUTHEAST COLORADO TO EASTERN NEW
MEXICO AND... AS THIS FEATURE DEEPENS TODAY IN RESPONSE TO AN
APPROACHING UPPER LOW... SOUTHERLY TO SOUTHEASTERLY WINDS WILL
INCREASE ACROSS THE REGION.

GIVEN AN INCREDIBLY MOIST AIRMASS... DIURNALLY DRIVEN SHOWERS AND
THUNDERSTORMS WILL DEVELOP LATE THIS MORNING AND INTO THE AFTERNOON
AS CONVECTIVE TEMPERATURES ARE REACHED. ONE OR TWO OF THESE STORMS
MAY BE ABLE TO BECOME STRONG /WITH ENOUGH SHEAR PRESENT TO OFFER
SOME HOPE FOR ORGANIZATION... BUT WEAK LAPSE RATES WILL HELP LIMIT
THIS POTENTIAL/. WILL CARRY 40-50 POPS THIS AFTERNOON FOR THIS
SCATTERED ACTIVITY WITH BETTER CHANCES FOR SEVERE WEATHER LATER
TONIGHT AND INTO SUNDAY MORNING AS A THUNDERSTORM COMPLEX
/ASSOCIATED WITH THE FIRST SHORTWAVE TROUGH/ APPROACHES FROM THE
WEST. GOOD LOW LEVEL SHEAR /0-1 KM BULK SHEAR VALUES AROUND 25 TO 30
KNOTS/ WILL CREATE CONCERNS FOR ISOLATED TORNADOES WITH THE
THUNDERSTORM COMPLEX AS WELL AS THE POTENTIAL FOR SOME DAMAGING WIND
IF SECTIONS OF THE LINE DO BOW. HIGH-RESOLUTION GUIDANCE PLACES THE
LEADING EDGE OF THIS ACTIVITY IN THE WESTERN ZONES BEFORE SUNRISE ON
SUNDAY WITH RAIN SPREADING ACROSS THE REGION BY MIDDAY. THIS COMPLEX
LOOKS TO CLEAR THE REGION SOMETIME SUNDAY EVENING.

ADDITIONALLY... THE COMBINATION OF PRECIPITABLE WATER VALUES NEAR 2
INCHES... MOIST LOW LEVEL INFLOW /DEW POINTS IN THE LOW 70S AND A 40
KNOT LOW LEVEL JET FEEDING INTO THE APPROACHING COMPLEX/... FORCING
FROM THE PASSING SHORTWAVE TROUGH... AND THE REGION/S LOCATION UNDER
THE RIGHT REAR QUADRANT OF AN UPPER JET ON SUNDAY SPELL OUT A
POTENTIALLY DANGEROUS FLASH FLOOD ENVIRONMENT FOR PARTS OF SOUTHEAST
TEXAS ON SUNDAY. WIDESPREAD ACCUMULATIONS OF 2 TO 4 INCHES WILL BE
POSSIBLE SUNDAY INTO MONDAY... WITH LOCALLY HIGHER AMOUNTS
APPROACHING 8 TO 11 INCHES POSSIBLE. FLASH FLOOD GUIDANCE HAS SHOWN
SOME IMPROVEMENT OVER THE PAST FEW DAYS /1 HOUR GUIDANCE GENERALLY
AROUND 3 INCHES/... BUT COLUMN INTEGRATED SOIL MOISTURE REMAINS
AROUND 65 TO 70 PERCENT PER THE NASA-SPORT LAND INFORMATION SYSTEM
AND IT WON/T TAKE MUCH TO CAUSE PROBLEMS... ESPECIALLY IF HIGHER
RAINFALL RATES ARE ACHIEVED.

HUFFMAN

&&

.LONG TERM...
SUNDAY NIGHT THROUGH FRIDAY.
FLASH FLOOD WATCH CONTINUES THROUGH MONDAY.

A COMPLEX/SWATH OF STORMS WITH HEAVY RAIN SHOULD BE MOVING EAST
OUT OF THE AREA SUNDAY NIGHT. MADDOX FAST TRAINING FLASH FLOODING
SCENARIO SHOULD BE COMING TO AN END BUT CONCERNS REMAIN AS THE
UPPER LOW IS STILL OVER NM/CO AND A VERY FAVORABLE COUPLED JET
STRUCTURE REMAINS OVER SETX. PW REMAIN AT 1.8 TO 2.1 WITH K INDEX
VALUES OF 35 TO 40 BLANKET MUCH OF THE AREA. IT IS POSSIBLE THAT
THE INITIAL S/W SWINGS THROUGH AND SHORT TERM RIDGING IN THE WAKE
OF IT BRINGS A LULL TO THE AREA SUNDAY NIGHT BUT CONCERNED THAT
WITH LLJ STILL HANGING IN THERE AROUND 25-30 KNOTS THAT THE FIRST
SYSTEM COULD LEAVE AN EAST TO WEST BOUNDARY FOR MORE STORMS TO
FORM ON PRIMARILY IN THE SOUTHERN HALF OF THE REGION. THEN DURING
THE DAY MONDAY THE NEXT S/W APPROACHES AND LLJ INTENSIFIES
TRANSPORTING THE NEXT SLUG OF MOISTURE BACK INTO THE AREA AND SETS
THE STAGE FOR ROUND 2 (OR 3). THOUGH THE SOUNDINGS LOOK MORE
UNSTABLE ON MONDAY AND 1000-500MB LAYER MOISTURE IS DOWN THE HEAVY
RAIN THREAT IS STILL VERY HIGH. WITH THESE SUCCESSIVE ROUNDS OF
HEAVY RAINFALL-LITTLE CHANCE FOR RUNOFF TO DISSIPATE-THE FLOODING
THREAT COULD BE EVEN WORSE ON MONDAY. RAINFALL TOTALS FOR THE
EVENT OF 2-4 INCHES WIDESPREAD AND ISOLATED TOTALS OF 8-11 INCHES
SEEMS QUITE REASONABLE. UNFORTUNATELY IF ALL THE CHEESE HOLES LINE
UP THEN AMOUNTS MUCH HIGHER COULD OCCUR. THIS COULD BE A VERY
DANGEROUS SITUATION MONDAY. IN ADDITION THE THREAT OF SEVERE IS
POSSIBLE BUT FOR NOW THINK IT IS MORE PRUDENT TO FOCUS THE THREAT
ON THE HEAVY RAIN EVEN THOUGH THE 06Z NAM/ECMWF FAVOR A HIGHLY
SHEARED ENVIRONMENT...THE MESOSCALE FACTORS MAY BE A BIG PLAYER BY
THE TIME MONDAY ROLLS AROUND. MONDAY NIGHT/TUESDAY MORNING THE
AXIS OF RICHEST MOISTURE TRANSPORT SHIFTS OUT TO THE EAST AND
ANOTHER BREAK COULD OCCUR. SOME OF THE GUIDANCE IS STILL SHOWING
THE POTENTIAL FOR MORE HEAVY RAIN ON TUESDAY WITH A RAIN COOLED
BOUNDARY BUT WITH LIGHTER WINDS THROUGH MOST OF THE COLUMN.

WEDNESDAY THROUGH FRIDAY THE PATTERN SHOULD TRANSITION TO MORE OF
A DIURNALLY DRIVEN PATTERN WITH DAYTIME HEATING THE MAIN MECHANISM
AS UPPER RIDGING SETS UP FOR A COUPLE OF DAYS BUT NOT STRONG
ENOUGH TO END THE PRECIP. TEMPERATURES DO FINALLY BOUNCE BACK UP
TO NORMAL BY WEDNESDAY AND THURSDAY.

45
&&


.MARINE...

AN APPROACHING STORM SYSTEM FROM THE WEST WILL RESULT IN INCREASING
ONSHORE WINDS AND SEAS OVER THE COASTAL WATERS TODAY... AND SMALL
CRAFT ADVISORIES ARE IN EFFECT BEGINNING THIS EVENING.
ADDITIONALLY... A THUNDERSTORM COMPLEX MAY REACH THE COASTAL
WATERS BY SUNDAY MORNING AND FURTHER DETERIORATION OF MARINE
CONDITIONS ARE EXPECTED IN AND NEAR THIS COMPLEX WITH HEAVY
RAIN...LIGHTNING... AND LOCALLY ENHANCED WINDS AND WAVES POSSIBLE.
ANOTHER ROUND OF THUNDERSTORMS WILL BE POSSIBLE OVER THE COASTAL
WATERS ON MONDAY. ALSO ON SUNDAY AND MONDAY... ABOVE NORMAL TIDES
COMBINING WITH SWELLS MAY LEAD TO MINOR FLOODING ON THE GULF
FACING BEACHES OF THE BOLIVAR PENINSULA. AN ELEVATED RISK FOR RIP
CURRENTS WILL ALSO CONTINUE ALONG THE UPPER TEXAS COAST THROUGH
THE REMAINDER OF THE WEEKEND.

HUFFMAN

&&


.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      82  70  78  71  81 /  50  50  80  50  90
HOUSTON (IAH)              84  73  81  74  81 /  40  40  80  80  90
GALVESTON (GLS)            84  77  82  78  82 /  30  40  80  80  90

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...FLASH FLOOD WATCH FROM THIS EVENING THROUGH MONDAY EVENING 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 ADVISORY FROM 7 PM THIS EVENING TO 1 PM CDT SUNDAY
     FOR THE FOLLOWING ZONES: GALVESTON BAY...MATAGORDA BAY...
     WATERS FROM FREEPORT TO THE MATAGORDA SHIP CHANNEL 20 NM TO
     60 NM...WATERS FROM FREEPORT TO THE MATAGORDA SHIP CHANNEL
     OUT 20 NM...WATERS FROM HIGH ISLAND TO FREEPORT 20 TO 60
     NM...WATERS FROM HIGH ISLAND TO FREEPORT OUT 20 NM.

     SMALL CRAFT SHOULD EXERCISE CAUTION THROUGH THIS EVENING FOR THE
     FOLLOWING ZONES: WATERS FROM FREEPORT TO THE MATAGORDA SHIP
     CHANNEL 20 NM TO 60 NM...WATERS FROM FREEPORT TO THE
     MATAGORDA SHIP CHANNEL OUT 20 NM...WATERS FROM HIGH ISLAND
     TO FREEPORT 20 TO 60 NM...WATERS FROM HIGH ISLAND TO
     FREEPORT OUT 20 NM.

&&

$$
SHORT TERM...HUFFMAN
LONG TERM...45


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