Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 301556
AFDHGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1056 AM CDT SAT MAY 30 2015

.DISCUSSION...
OUTFLOW BOUNDARY HAS PUSHED INTO SE TX FROM CONVECTION OVER N TX
THIS MORNING. THIS ALONG WITH DIURNAL HEATING HAVE ALLOWED FOR A
FEW SCT SHOWERS AND STORMS TO FORM MAINLY ALONG US 59 FROM HOUSTON
TO LUFKIN. OTHER ISO COVECTIVE CELLS HAVE FORMED FROM COLUMBUS TO
PALACIOS. MOST OF THIS ACTIVITY SEEMS TO PULSE IN INTENSITY WITH
MAYBE RAIN RATES OF HALF INCH AN HOUR. THE MAIN TREND TO NOTE IS
THAT STORMS ARE NOT MOVING VERY MUCH. LATEST SFC ANALYSIS HAS COLD
FRONT PUSHING THROUGH N TX INTO W C TX. FRONT SHOULD BE MAKING ITS
WAY TO SE TX THIS AFTERNOON. BEGINNING OF THE FRONT SHOULD REACH
COLLEGE STATION/CROCKETT LINE 3-4PM AND THEN HOUSTON AREA 6-7PM
BASED ON LATEST HRRR RUN.

LATEST SHORT RANGE GUIDANCE STILL HAS STORMS FORMING ON SEA
BREEZE EARLY AFTERNOON AND THEN ALONG THE FRONT LATER THIS
AFTERNOON. MAIN CONCERN WILL BE FOR HEAVY RAINFALL AS STORMS WILL
NOT BE MOVING QUIKCLY. RAIN RATES OF 1-2 INCHES FOR A COUPLE OF
HRS WILL CAUSE FLOODING PROBLEMS. WE ARE STILL LOOKING AT VERY
SATURATED GROUNDS WHICH MEANS EVEN 2-3 INCHES OF RAIN COULD CAUSE
FLOODING PROBLEMS. FOR NOW WE WILL KEEP FLASH FLOOD WATCH AS IS
BUT WILL EVALUATE THE NEED FOR A WATCH FOR SOME OF THE NORTHERN
PORTIONS OF THE FORECAST AREA DEPENDING ON THE EVOLUTION OF
CONVECTION.

39

&&

.PREV DISCUSSION... /ISSUED 628 AM CDT SAT MAY 30 2015/

DISCUSSION...
SEE THE 12Z AVIATION DISCUSSION BELOW.

40

AVIATION...
THE SQUALL LINE OVER THE HILL COUNTRY MAY HOLD TOGETHER TO AFFECT
KCLL AND KUTS BEFORE 15Z. THE LATEST HIGH RES MODELS ARE HOLDING
BACK ON THUNDERSTORM CHANCES AT THESE TWO SITES UNTIL MID MORNING.
THIS MAY PAN OUT AS THE LATEST RADAR INDICATES THAT THE SQUALL
LINE WAS WEAKENING AT 11Z AS IT WAS MOVING TOWARD THE KGRK RADAR
SITE. WILL UPDATE THE FORECAST FOR THESE LOCATIONS IF THESE STORMS
HOLD TOGETHER.

KEPT THE SAME TIMING FOR THE MOST PART AS IN THE LAST FORECAST
PACKAGE. BY MID MORNING BETTER CHANCES FOR SHOWERS WILL DEVELOP
AND BY MIDDAY THUNDERSTORM CHANCES WILL BECOME BETTER. THERE ARE
SOME INDICATIONS THAT THE STORMS MOVING IN FROM THE NORTHWEST WILL
MERGE WITH SHOWERS AND THUNDERSTORMS DEVELOPING ALONG THE
SEABREEZE. IF SO...THE HOUSTON METRO AIRPORTS MAY HAVE ADVERSE
IMPACTS FROM THUNDERSTORMS FROM 18Z TO 03Z. AFTER A BREAK...THE
NAM12 BRINGS ANOTHER CHANCE FOR THUNDERSTORMS FROM KCXO TO THE
COAST AFTER 09Z.

40

PREV DISCUSSION... /ISSUED 400 AM CDT SAT MAY 30 2015/

DISCUSSION...
AT 3 AM...A COLD FRONT EXTENDED FROM ABOUT OKLAHOMA CITY TO
ABILENE TO FORT STOCKTON. SHRA/TSRA CONTINUE TO DEVELOP ALONG THE
FRONT AS IT SURGES SOUTH...AND PUSHES EAST A BIT MORE SLOWLY.
SATELLITE DERIVED PW VALUES SHOW 1.6-1.9 INCHES ACROSS SOUTHEAST
TEXAS. FCST SOUNDINGS SHOW CONVECTIVE TEMPS AROUND 82 DEGREES.
UPPER LEVEL WINDS ARE BROADLY DIVERGENT AND ARE PROGGED TO REMAIN
DIVERGENT THROUGH SUNDAY MORNING. SE TX WILL BRIEFLY LIE IN A
RIGHT REAR QUAD SATURDAY NIGHT. SHRA/TSRA WILL BEGIN TO DEVELOP
ALONG THE COAST BETWEEN 15-17Z AS TEMPS WARM INTO THE LOWER 80S.
THE COLD FRONT OVER NORTH TEXAS WILL BE PUSHING SOUTH AND EAST AND
WILL REACH THE NORTHERN ZONES ABOUT 18Z. THE SEA BREEZE WILL BEGIN
TO WORK INLAND DURING THE AFTN AS THE FRONT CONTINUES TO PUSH
SOUTH AND THE TWO FEATURES SHOULD MERGE OVER SE TX DURING THE
AFTN. THE NAM 12 IS VERY AGGRESSIVE WITH THE SEA BREEZE/FRONT
COLLIDING AROUND 21Z WITH VERY HEAVY RAIN DEVELOPING ALONG THE
U.S. HIGHWAY 59 CORRIDOR. THE NAM IS PRODUCING 3-4 INCHES OF RAIN
ACROSS HARRIS...BRAZORIA AND FT BEND COUNTIES. THE QPF OUTPUT FROM
THE GFS AND ECMWF ARE MORE BENIGN BUT THEY ARE BASICALLY ON THE
SAME PAGE WITH A WEAK SEA BREEZE MERGING WITH THE COLD FRONT. WILL
MAINTAIN THE FLASH FLOOD WATCH AS IS BUT FEEL THE THREAT FOR
EXCESSIVE RAIN WILL FOCUS OVER THE CENTRAL ZONES. THINK THE WATCH
WILL BE TRIMMED FROM THE NORTH TOWARD EVENING ONCE CONVECTIVE
TRENDS BECOME CLEAR.

THE FRONT WILL MEANDER OVER THE SOUTHERN HALF OF SOUTHEAST TEXAS
THROUGH EARLY SUNDAY MORNING. THE COMBINATION OF THE FRONT AND A
TROUGH AT 500 MB WILL LEAD TO ADDITIONAL SHOWERS OVERNIGHT INTO
SUNDAY. DRIER AIR WILL WORK INTO THE AREA SUNDAY AFTERNOON AND
RAIN CHANCES WILL DECREASE DURING THE AFTN.

THE UPPER LEVEL TROUGH WILL PUSH EAST ON MONDAY BUT IT LOOKS
CLOSE ENOUGH TO STILL TRIGGER A FEW AFTN SHRA/TSRA OVER THE
EASTERN ZONES ON MON. UPPER LEVEL RIDGING WILL BUILD ACROSS SOUTH
TEXAS TUE-FRI. SUBSIDENCE FROM THE RIDGE SHOULD LIMIT RAIN CHANCES
AND ALLOW TEMPS TO WARM TO NEAR 90 DEGREES BY THE END OF NEXT
WEEK. 43

MARINE...
WINDS AND SEAS MAY BRIEFLY GET TO ABOVE CAUTION LEVELS WITH
THUNDERSTORMS LATER TODAY AND TONIGHT. A FRONTAL BOUNDARY IS
FORECAST BY THE MODELS TO MOVE OFF THE COAST LATER TONIGHT OR ON
SUNDAY. THE FRONT IS THEN FORECAST TO DISSIPATE AS HIGH PRESSURE
BUILDS INTO THE NORTHWESTERN GULF INTO THE MID WEEK PERIOD.

40

&&

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      85  67  81  64  85 /  70  50  30  10  20
HOUSTON (IAH)              87  70  83  66  87 /  80  70  50  20  30
GALVESTON (GLS)            85  75  81  74  81 /  50  50  50  30  30

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...FLASH FLOOD WATCH THROUGH SUNDAY MORNING 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...NONE.
&&

$$

DISCUSSION...39


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