Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 270525 AAB
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
1225 AM CDT WED AUG 27 2014

.DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

&&

.AVIATION...MOISTURE IS INCREASING THROUGH THE ATMOSPHERE FROM
NORTHEAST TO SOUTHWEST ACROSS THE AREA. THE VALLEY METRO AREAS
LOOK TO BE DRIER FOR NOW BUT THAT MAY CHANGE BY SUNRISE WITH
HIGHER LOW LEVEL HUMIDITY POSSIBLY PRODUCING PATCHY MVFR CIGS AT
AROUND 2500 FT BY SUNRISE AMID LIGHT WINDS.

DAYTIME HEATING SHOULD SPARK SHOWERS AND THUNDERSTORMS AMID THE
MORE MOIST ENVIRONMENT TOMORROW. COVERAGE AND INTENSITY REMAINS
FAIRLY LOW CONFIDENCE AND KEPT THE CONVECTIVE WORDING MORE
OPTIMISTIC IN THE TAFS WITH HOPES THAT THE NEXT CYCLE WILL PROVIDE
ENOUGH INSIGHT TO INCLUDE THUNDER GROUPS IF NECESSARY WITH MORE
ACCURATE TIMING THAN CAN BE PROVIDED FROM 06Z. PREVAILING
CONDITIONS SHOULD BE VFR WITH MVFR VIS/CIG INVOF HEAVIER CONVECTION.

WIND SPEEDS WILL DECREASE AFTER SUNSET LIKELY OUT OF THE NORTHWEST
WITH BEST BETS FOR NOW ON HIGH MVFR CIG AMID A VERY MOIST LOW
LEVEL AIRMASS. /68-JGG/

&&

.PREV DISCUSSION... /ISSUED 645 PM CDT TUE AUG 26 2014/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...GUSTY EAST WINDS WILL BEGIN TO DIMINISH AFTER SUNSET.
LIGHT WINDS WILL DEVELOP LATER THIS EVENING THROUGH THE OVERNIGHT
HOURS. VFR CONDITIONS WILL PREVAIL ACROSS THE RIO GRANDE VALLEY
THIS EVENING COURTESY OF A SLIGHTLY DRIER ATMOSPHERE. MOISTURE
BEGINS TO INCREASE ACROSS THE AREA LATER TONIGHT. THIS MAY RESULT
IN THE DEVELOPMENT OF SOME PATCHY STRATUS OR ISOLATED GROUND
FOG...WITH BRIEF MVFR CEILINGS POSSIBLE AROUND SUNRISE.
OTHERWISE...VFR CONDITIONS EXPECTED TO PREVAIL ON WEDNESDAY WITH
LIGHT TO MODERATE NORTHEAST WINDS. SHOWERS OR THUNDERSTORMS ARE
ANTICIPATED LATE MORNING INTO THE AFTERNOON WITH THE SEA BREEZE BUT
CONFIDENCE TO ADD FOR THIS TAF CYCLE REMAINS LOW AT THIS TIME.
HOWEVER...WILL MENTION VCSH AT ALL TAF SITES AFTER 15Z.

PREV DISCUSSION... /ISSUED 257 PM CDT TUE AUG 26 2014/

.A MORE WET WEATHER PATTERN EXPECTED FOR THE LONG TERM FORECAST
ACROSS THE RGV...

SHORT TERM.../NOW THROUGH WEDNESDAY NIGHT/...
BROAD SURFACE LOW PRESSURE TROUGH LIES ALONG THE NORTHERN GULF WITH
AN INVERTED MID LEVEL TROUGH WEST OF THE YUCATAN. UPPER RIDGE
RESIDES OVER OVER FLORIDA AND THE SOUTHEAST GULF. THE BROAD CYCLONIC
CIRCULATION ASSOCIATED WITH THE SURFACE TROUGH HAS KEPT US RAINFREE
TODAY WITH A VERY WEAK SEA BREEZE DUE MORE TO THE THERMAL CONTRAST
THAN A MOISTURE DISCONTINUITY. THE MORNING SOUNDING INDICATED ONLY
1.54 INCHES OF PWAT WHICH IS 86 PERCENT OF NORMAL. SOME CONVECTION
ALONG THE SOUTHWESTERN PERIPHERY OF THE TROUGH AXIS HAS BEEN DODGING
THE FAR OFFSHORE COASTAL WATERS MUCH OF THE DAY BUT IS WANING THIS
AFTERNOON.

TONIGHT...WITH THE WEAK SEABREEZE AND LIGHT OFFSHORE FLOW DO NOT
EXPECT ANY CONVECTION THIS EVENING. MOISTURE DOES BEGIN TO INCREASE
AS THE MID LEVEL TROUGH AND SURFACE TROUGH CONTINUE TO DRIFT SLOWLY
WEST. PREVIOUS FORECAST AND MODEL RUN INDICATED A QUICKER WESTWARD
MOVEMENT OF THE TROUGH BUT THIS MORNING`S PACKAGE IS TRENDING
SLOWER. MOISTURE HOWEVER DOES BEGIN TO INCREASE AFTER MIDNIGHT AND
ESPECIALLY BY 12Z WEDNESDAY WITH THE GFS INDICATING PWATS NEARING 2
INCHES. EXPECTING NOCTURNAL CONVECTION OVER THE OFFSHORE WATERS
AFTER MIDNIGHT BUT CONFIDENCE IS LOW ON MOVING SHOWERS INLAND PRIOR
TO SUNRISE. WILL KEEP POPS AT 10 PERCENT FOR THE COASTAL COUNTIES
OVERNIGHT WITH CHANCE POPS OVER THE FAR OFFSHORE. TEMPERATURES WARM
AND MUGGY OVERNIGHT BUT WITH LIGHT WINDS MID TO UPPER 70S SHOULD
SUFFICE.

WEDNESDAY...MOISTURE VALUES AND DEPTH INCREASE ON WEDNESDAY WITH THE
APPROACH OF THE MID LEVEL AND SURFACE TROUGH. PWATS ARE EXCEEDING 2
INCHES HOWEVER WITH THE SLOW WESTERN TRACK DIVERGENT FLOW IS LACKING
FOR WIDESPREAD ACTIVITY TO DEVELOP. NAM REMAINS THE MOST AGGRESSIVE
WITH POPS APPROACHING 60 PERCENT IN SOME COASTAL LOCATIONS. GFS AND
ECMWF ARE MORE CONSERVATIVE AT THIS POINT AS IS THE FORECAST.
EXPECTING A MORE ACTIVE SEA BREEZE MID TO LATE MORNING AND INTO THE
AFTERNOON. BRIEF HEAVY RAIN IS POSSIBLE WITH THE SURFACE TO 500MB
FLOW REMAIN AT OR BELOW 10 KNOTS. TEMPERATURES WILL BE HIGHLY
DEPENDENT ON WHEN AND WHERE THE RAIN FALLS. MODEL GUIDANCE IS
SHOWING LOWER TEMPERATURES THAN THE LAST SEVERAL WEEKS WILL TREND
JUST SLIGHTLY HIGHER THAN THE CONSENSUS.

WEDNESDAY NIGHT...THIS PERIOD COULD BE AT A TIPPING POINT DEPENDING
ON IF A MORE TROPICAL ATMOSPHERE TAKES OVER. NOCTURNAL SHOWERS AND
THUNDERSTORMS ARE ANTICIPATED TO DEVELOP OFFSHORE BUT UNSURE HOW
MUCH AND WHEN THE ACTIVITY WILL APPROACH THE COASTAL ZONES AND IF
SUFFICIENT SUPPORT TO MAINTAIN THE CONVECTION AS IT MOVES INLAND.
SURFACE TROUGH TO REMAIN IN TACT WITH A MID TO UPPER LEVEL LOW
SITTING OVER THE LOWER TEXAS COAST AND WESTERN GULF. POP FORECAST
IS CONSERVATIVE WITH LACK OF HEATING HOWEVER IF TROPICAL SHOWERS DO
DEVELOP INCREASING DIVERGENT FLOW COULD ALLOW FOR A BIT MORE
WIDESPREAD ACTIVITY. COASTAL COUNTIES WILL HAVE THE BEST CHANCES
WITH MODEL GUIDANCE SHOWING SOME CHANCE THROUGH THE OVERNIGHT HOURS
ALONG AND EAST OF HIGHWAY 281/69C. AN UPWARD BUMP IN POPS IS NOT OUT
OF THE QUESTION BUT WILL WAIT FOR AT LEAST ANOTHER MODEL RUN BEFORE
GOING ABOVE AND BEYOND GUIDANCE.

LONG TERM...THURSDAY THROUGH TUESDAY NIGHT...A BROAD RIDGE ACROSS
THE SOUTHERN PORTION OF THE STATE BEGINS TO SHIFTS EAST AS AN
UPPER LEVEL TROUGH MOVES ACROSS THE GREAT BASIN INTO THE FOUR
CORNERS REGION THURSDAY. A WEAK DISTURBANCE OVER THE NORTHERN GULF
COAST WILL MIGRATE W TO SW ALONG THE WESTERN GULF COAST THURSDAY.
THIS TROPICAL WAVE COMBINED WITH A WEAK INVERTED TROUGH MOVING
INTO THE REGION WILL SUPPORT FAVORABLE CONDITIONS FOR CONVECTION
TO INCREASE THROUGH THE END OF THE WEEK. AT THIS TIME... NHC KEEPS
THIS AREA OF DISORGANIZE SHOWERS AND THUNDERSTORMS WITH A LOW 10%
OF DEVELOPMENT DURING THE NEXT 48 HOURS AS THE UPPER LEVEL WINDS
WILL NOT BE FAVORABLE FOR ANY SIGNIFICANT DEVELOPMENT. WITH THAT
SAID...THERE IS MORE CONFIDENCE THAT THE POTENTIAL FOR RAIN WILL
INCREASE ACROSS THE AREA SO LEAN TOWARDS A BIT HIGHER POPS THU
DURING THE DAY OVER THE GULF WATERS AND MOVING INLAND EARLIER IN
THE DAY AS SEA BREEZE WILL LIKELY INITIATE EARLIER. THE MOISTURE
CONTENT WILL BE THERE AS WELL WITH LATEST 12Z GFS SOUNDING SHOWING
DEEPER ONSHORE FLOW WITH PRECIPITABLE WATER VALUES ON AVERAGE
AROUND 2.2 IN. AS THIS DISTURBANCE MOVES WEST THURSDAY...THE
CONVECTION WILL PROGRESS WESTWARD LATE THURSDAY INTO FRIDAY. THIS
SHOULD SUPPORT SOME ENHANCE RAINS MOVING INTO THE CWA WITH SOME
0.25 TO 0.50+ INCHES AREAL AVERAGE RAINS LIKELY. BEST QPF WILL BE
THURSDAY AND FRIDAY. SINCE MORE CLOUD COVER IS EXPECTED TO DEVELOP
WITH THE INSTABILITY IN THE AREA...LEAN TOWARDS HIGH TEMPERATURES
REMAINING IN THE LOW TO MID 90S AND FRIDAY IN THE UPPER 90S CLOSE
TO 100S BUT NOT AS HOT COMPARED TO PREVIOUS DAYS.

THE CHANCE OF RAIN DECREASE BY THE WEEKEND AS DEEPER MOISTURE GETS
PULL NORTHEAST AND UPPER HIGH SHIFTS SLIGHTLY EASTWARD. A MORE ZONAL
FLOW PATTERN DEVELOPS ACROSS THE DESERT SOUTHWEST AND THE CENTRAL
PLAINS BRINGING BACK DRY AND BREEZE PATTERN ACROSS DEEP SOUTH TX. AN
UPPER TROUGH MOVES EAST ACROSS THE NORTHERN CANADIAN BORDER SUNDAY
DEEPENING LEE SIDE TROUGH TOWARDS THE CENTRAL PLAIN. THIS WILL
STRENGTHEN THERMAL LOW OVER WEST TEXAS AND INCREASE SOUTHEAST WINDS
ACROSS THE CWA. AS THE DRY WEATHER PATTERN AND THE LACK OF CLOUD
COVER RETURNS...EXPECT THE TEMPERATURES TO RISE BACK TO THE TRIPLE
DIGITS ACROSS THE WESTERN COUNTIES. INCREASE TEMPS ACROSS THE WEST 2
TO 3 DEGREES ABOVE GUIDANCE SUNDAY AND MONDAY ESPECIALLY ACROSS THE
WEST. FOR EARLY NEXT WEEK...CHANCE OF RAIN RETURN OVER THE GULF
WATERS MONDAY AFTERNOON AND TUESDAY FROM A WEAK TROPICAL WAVE OVER
THE BAY OF CAMPECHE MIGRATING WESTWARD.

MARINE...NOW THROUGH WEDNESDAY...BROAD SURFACE TROUGH OVER THE
NORTHERN GULF TO MOVE SLOWLY WEST-SOUTHWEST THROUGH THURSDAY
MORNING. LIGHT OFFSHORE FLOW IS EXPECTED THROUGH WEDNESDAY KEEPING
SEA RATHER LOW. WIND TO TURN MORE EAST TO SOUTHEAST WEDNESDAY
NIGHT WITH A SLIGHT INCREASE IN WINDS AND SEAS. SHOWERS AND
THUNDERSTORMS ARE EXPECTED TO INCREASE IN AREAL COVER AFTER
MIDNIGHT TONIGHT THROUGH WEDNESDAY NIGHT. HIGHER WINDS AND SEAS
ARE EXPECTED DUE TO THE CONVECTION.

THURSDAY THROUGH MONDAY NIGHT...A WEAK LOW PRESSURE OVER THE
NORTHERN GULF COAST WILL MOVE WEST TO SOUTHWEST THE NEXT FEW DAYS
ENHANCING SHOWERS AND THUNDERSTORMS OVER THE GULF WATERS. THIS
ACTIVITY WILL PRODUCE GUSTY WINDS...MODERATE TO HEAVY RAIN AND
OCCASIONAL LIGHTNING. EXPECT THIS ACTIVITY TO INCREASE THURSDAY
THROUGH FRIDAY AS THE DEEPER MOISTURE AND THE UPPER LEVEL SUPPORT
MOVES INTO THE GULF WATERS. THE WINDS WILL REMAIN MODERATE AND
SEAS AROUND 2 TO 4 FEET WITH A WEAK PRESSURE GRADIENT IN PLACE. BY
FRIDAY INTO THE WEEKEND...CHANCE OF RAIN WEAKEN AS THE WAVE MOVES
WESTWARD AND DRY AIR INFILTRATES INTO THE AREA. MOST OF THE DEEPER
MOISTURE ALSO MOVES NORTHEAST AS UPPER HIGH SHIFTS EAST. THE
SOUTHEAST WINDS BEGIN TO INCREASE BY THE END OF THE WEEKEND AND
INTO NEXT WEEK...AS ANOTHER LOW PRESSURE SYSTEM OVER THE NORTHWEST
DEEPENS A SURFACE LOW ACROSS THE CENTRAL PLAINS. THIS WILL
STRENGTHEN SURFACE WINDS ACROSS THE GULF WATERS. EXPECT BREEZE SE
WINDS RETURNING MONDAY AFTERNOON AND TUESDAY. CONDITIONS WILL BE
CLOSE TO SCEC POSSIBLY AT NIGHT OVER THE GULF WATERS MONDAY NIGHT
INTO TUESDAY. SEAS WILL INCREASE BETWEEN 3 TO 5 OR 4 TO 6 FEET
OVER THE WEEKEND. EXERCISE CAUTION CONDITIONS MAY BE POSSIBLE
SATURDAY INTO SUNDAY AS A RESULT.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  94  79  92  79 /  30  30  30  30
BROWNSVILLE          97  78  94  79 /  30  20  40  40
HARLINGEN            98  76  96  78 /  40  20  40  40
MCALLEN             101  79  99  79 /  30  20  40  40
RIO GRANDE CITY     102  79 100  79 /  20  10  30  40
SOUTH PADRE ISLAND   90  78  89  80 /  30  30  40  30

&&

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

$$

THIS PRODUCT IS ALSO AVAILABLE ON THE WEB AT:
HTTP://WEATHER.GOV/RGV

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