Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 281149
AFDHGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
649 AM CDT SUN JUN 28 2015

.AVIATION...
FOR THE 12Z TAFS... MAIN AVIATION CONCERNS CENTER AROUND TIMING
FOR TSRA/SHRA AT THE TERMINALS TODAY.

LOW CONFIDENCE HEADING INTO THE FIRST 6-12 HOURS OF THE TAF WITH
POOR INITIALIZATION OF LATEST HIGH-RESOLUTION GUIDANCE. CONVECTION
CONTINUES TO DEVELOP ALONG A WEST TO EAST ORIENTED BOUNDARY SLOWLY
SAGGING ESE THIS MORNING. BASED ON IR SATELLITE AND RADAR
TRENDS... ANTICIPATE ACTIVITY TO IMPACT HOUSTON TERMINALS THROUGH
AT LEAST 14Z WITH IFR TO MVFR VISIBILITIES FROM HEAVY RAINFALL
TEMPORARILY OCCURRING AS THIS ACTIVITY SLOWLY SAGS ACROSS HARRIS
COUNTY. MAIN BOUNDARY IS EXPECTED TO WASH OUT THROUGHOUT THE
DAY... BUT CONTINUING VCTS MENTION FOR HOUSTON TERMINALS THROUGH
EARLY EVENING GIVEN UNCERTAINTY OF PLACEMENT. ADDITIONALLY...
DAYTIME HEATING MAY CONTRIBUTE TO AFTERNOON/EARLY EVENING
DEVELOPMENT OF TSRA/SHRA FOR ALL OTHER TERMINALS AND HAVE ADDED
VCTS MENTION FOR ALL OTHER TERMINALS STARTING 18-20Z. WILL
CONTINUE TO MONITOR TRENDS... AMENDING AS NECESSARY. OTHERWISE...
LIGHT AND VARIABLE TO LIGHT AND W/SW WINDS TODAY EXPECTED TO
BECOME LIGHT AND SOUTHERLY BY THE END OF THE PERIOD.

HUFFMAN

&&

.PREV DISCUSSION... /ISSUED 411 AM CDT SUN JUN 28 2015/

DISCUSSION...
BIT OF A DIFFICULT FORECAST FOR TODAY. SE TEXAS WAS CAUGHT IN A
WEAKNESS IN THE RIDGE ALOFT...ALTHOUGH THERE WAS A 200-300 MB
UPPER LOW OFF BROWNSVILLE AND A 200-300 MB TROUGH OVER THE
NORTHEASTERN PART OF THE STATE THAT EXTENDED TO THE NORTHERN
COUNTIES OF THE COUNTY WARNING AND FORECAST AREA. THE RAP40 MEAN
700-300MB FLOW SHOWED THE WEAKNESS QUITE WELL OVER THE COASTAL
AREAS AT 4 AM. PLENTY OF MOISTURE WAS AVAILABLE UP THROUGH 700 MB
AS WELL.

GIVEN THE WEAK FLOW ALOFT...THE MODELS WERE NOT HANDLING THE
FORECAST QPF FIELDS VERY WELL. THE BEST SO FAR HAS BEEN THE HIGH
RES ARW/NMM. THESE TWO MODELS SHOW A BREAK IN THE ACTIVITY BETWEEN
ABOUT SUNRISE AND MID MORNING. THE COARSER RESOLUTION MODELS SUCH
AS THE GFS90 AND ECMWF KEPT DECENT AREAS OF RAINFALL POTENTIAL
OVER MAINLY THE CENTRAL AND SOUTHERN COUNTIES FOR MOST OF THE DAY.
THE THINKING HERE IS THAT THE ACTIVITY OCCURRING BETWEEN BRENHAM
AND CLEVELAND AT 4 AM WILL GRADUALLY SINK EAST-SOUTHEASTWARD AND
DISSIPATE AROUND OR SHORTLY AFTER SUNRISE. DAYTIME HEATING WILL
THEN LEAD TO MORE DEVELOPMENT POSSIBLY LATER THIS MORNING AND
MOST LIKELY THIS AFTERNOON. HOWEVER...GIVEN THE LOW CONFIDENCE IN
THE MODEL SOLUTIONS...WILL NOT TRY AND PINPOINT THE TIME PERIODS
IN THE FORECAST. IT IS A GIVEN THAT LOCALLY HEAVY RAINFALL WILL BE
POSSIBLE...ESPECIALLY EARLY THIS MORNING WITH THE SLOW MOVEMENT OF
THE STORMS AND WITH PW/S AROUND 2 INCHES.

THE MODEL CONSENSUS IS FOR CHANCES FOR SHOWERS AND THUNDERSTORMS
MAINLY DURING THE DAYTIME FOR THE MONDAY THROUGH WEDNESDAY TIME
PERIOD. THE WEAKNESS ALOFT REMAINS OVERHEAD AND A WEAK SURFACE
BOUNDARY APPEARS TO REMAIN AT LEAST NEARBY. THURSDAY AND FRIDAY
MAY SEE SOME SLIGHTLY HIGHER HEIGHTS AT 500 MB WHICH AT LEAST
HINTS THAT THE RIDGE WILL BE TRYING TO BUILD OVERHEAD. BOTH THE
GFS AND ECMWF AGREE WITH THE EASTERN RIDGE BUILDING SLIGHTLY INTO
THE AREA BY THE END OF THE WEEK...ALTHOUGH A MODEL CONSENSUS DOES
UP THE RAIN CHANCES A BIT ON SATURDAY DUE MAINLY TO THE
SEABREEZE.

40

MARINE...
LATEST MARINE AND COASTAL OBSERVATIONS SHOW SOMETHING OF A
CONVERGENCE ZONE/ BOUNDARY FROM NEAR KXIH TO KSCF AND HIGH
RESOLUTION GUIDANCE INDICATES THIS FEATURE MAY SERVE AS A FOCUS
FOR A BROKEN LINE OF SHOWERS AND THUNDERSTORMS TO DEVELOP OVER THE
COASTAL WATERS TODAY. AS OF 3 AM CDT... A FEW OF THESE SHOWERS HAD
ALREADY BEGUN DEVELOPING OVER THE EASTERN WATERS WITH ADDITIONAL
DEVELOPMENT EXPECTED THROUGH THE REMAINDER OF THE MORNING HOURS.
NEAR THUNDERSTORMS...LOCALLY ENHANCED WINDS AND WAVES WILL BE
POSSIBLE IN ADDITION TO REDUCED VISIBILITIES. SHOWER AND
THUNDERSTORM CHANCES WILL PERSIST THROUGH MID-WEEK WITH AN UPPER
LEVEL WEAKNESS OVER THE WESTERN GULF OF MEXICO. OTHERWISE...LIGHT
TO OCCASIONALLY MODERATE ONSHORE FLOW EXPECTED TO PERSIST OVER THE
NEXT FEW DAYS.

HUFFMAN

&&

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      91  74  90  74  89 /  30  20  30  20  40
HOUSTON (IAH)              91  75  92  76  89 /  50  30  40  20  40
GALVESTON (GLS)            88  80  90  81  88 /  50  30  30  20  40

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION UNTIL 8 AM CDT THIS MORNING
     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.

&&

$$

AVIATION/MARINE...14


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