Area Forecast Discussion
Issued by NWS Brownsville, TX

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000
FXUS64 KBRO 311127
AFDBRO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
627 AM CDT THU JUL 31 2014

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

&&

.AVIATION...PESKY INTERMITTENT MVFR WILL SWITCH BETWEEN BKN AND
SCT AT 2000 FT THROUGH THE NEXT TWO TO THREE HOURS. LEANED THE
FORECAST BACK TO PREVAILING VFR IN THE NEW PACKAGE. SOUTHEAST
WINDS WILL INCREASE THROUGH MID MORNING GUSTING 23 TO 27 KNOTS
THROUGH SUNSET. PREVAILING VFR EXPECTED THROUGH THE OVERNIGHT. /68-JGG/

&&

.PREV DISCUSSION... /ISSUED 345 AM CDT THU JUL 31 2014/

SHORT TERM /NOW THROUGH THURSDAY NIGHT/...
BOUNDARY LAYER HAS NOT FULLY DECOUPLED TONIGHT WITH 10 TO 15 MPH
WINDS CONTINUING...A LITTLE GUSTIER WEST OF 281 WHERE RAP/NAM
ANALYZE ABOUT A 30 TO 40 KNOT NOCTURNAL LOW LEVEL JET THAT SHOULD
DIMINISH SIGNIFICANTLY AFTER SUNRISE. WATER VAPOR SHOWS FAIRLY
LARGE TROUGH OVER THE EASTERN HALF OF THE US DIGGING SOUTHEASTWARD
STEADILY. A SURFACE FRONT CONTINUES TO TRUCK SOUTHWARD INTO THE
HILL COUNTRY AND BIG BEND REGION. ATMOSPHERIC AND LOW LEVEL
MOISTURE IS SLIGHTLY RICHER THAN IT WAS 24 HOURS AGO.

TODAY...SURFACE PRESSURE GRADIENT SHOULD BE QUITE SIMILAR TO
YESTERDAY MUCH OF THE DAY MAKING FOR A BREEZY DAY...ESPECIALLY IN
THE COASTAL COUNTIES CORRIDOR. MEAGER 850-700MB RH AND A RESIDUAL
TEMPERATURE INVERSION...COUPLED WITH POOR CONDITIONS FOR A SEA
BREEZE WILL KEEP THE WEATHER DRY. HEAT WILL BE THE MAIN PLAYER.
COLUMN MOISTURE IS SLIGHTLY HIGHER THAN 24 HOURS AGO AND FORECAST
HEAT INDEX VALUES ARE ABOUT 2 DEGREES WARMER THAN WEDNESDAY AS
WELL. VALUES OF 108 TO 111 WILL BE COMMONPLACE...WHICH IS RIGHT UP
AGAINST BUT SLIGHTLY BELOW LOCAL EAT ADVISORY CRITERIA. NOT
EXPECTING CONDITIONS TO BE DIFFERENT ENOUGH FROM LAST WEEK OR TWO
TO JUMP ON AN ADVISORY IN BUT CAN NOT COMPLETELY RULE OUT THE NEED
FOR ONE AS THE DAY PROGRESSES.

TONIGHT...SURFACE TROUGHING AND THE ASSOCIATED FRONT SHOULD
SLOW/STALL TO THE NORTH OF THE CWA TONIGHT BUT IT WILL LIKELY BE
CLOSE ENOUGH TO BROADEN THE LOCAL PRESSURE GRADIENT. THIS SHOULD
ALLOW WIND SPEEDS TO RELAX IN THE OVERNIGHT. CURRENT FORECAST
PRODUCES ENOUGH MIDDLE CLOUD TO KEEP FOG FORMATION AT BAY BUT WILL
HAVE TO MONITOR FOR AT LEAST PATCHY FOG AND CONSIDER INCLUDING
LATER IF CONDITIONS CHANGE.

FRIDAY...THE LARGE EASTERN US TROUGH SLIDES FAR ENOUGH SOUTH TO
PUT THE REGION IN NORTHWESTERLY FLOW ALOFT. THIS NUDGES THE
TROUGHING/FRONT FURTHER SOUTH AND PRODUCES A SORT OF BROAD AND
WEAK CONVERGENCE ACROSS MOST OF SOUTHERN TEXAS. EMBEDDED SHORTWAVE
TROUGHS APPEAR TO AID IN PRODUCING SHOWER AND THUNDERSTORM
ACTIVITY TO THE NORTH AND IN THE 00Z GUIDANCE SUITE BRINGS IT INTO
MAINLY THE NORTHWESTERN THIRD OF DEEP SOUTH TEXAS. 850-700MB RH
INCREASES SUBSTANTIALLY IN THIS ZONE OF CONVERGENCE...WITH GOOD
AGREEMENT BETWEEN NAM/GFS/ECMWF ON ABOUT 80PCT 850-700MB RH AMID
MODESTLY UNSTABLE MIXED LAYER PARCELS. ADJUSTED POPS UPWARD WITH A
20 PCT/SLIGHT CHANCE OF SHOWERS AND STORMS AIDED BY THE SEA BREEZE
MAINLY NORTH OF THE RGV METRO AREAS...AND A 30 PCT CHANCE OF
SHOWERS AND STORMS NORTHWEST OF A FALCON DAM TO FALFURRIAS LINE IN
THE LATE AFTERNOON. SYNOPTIC SCALE WIND SPEEDS SHOULD SLACKEN
QUITE A BIT AS THE TROUGHING GETS CLOSER WHICH WILL MAKE FOR A
STRONGER SEA BREEZE BOUNDARY AND A BETTER CHANCE IT AIDS IN
INITIATING AT LEAST SOME SHOWER OR POSSIBLY THUNDERSTORM ACTIVITY.
MAX TEMPS WILL BE DOWN 2 TO 4 DEGREES MODERATED BY INCREASED
CLOUD COVER AND COLUMN RELATIVE HUMIDITY.

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...AS MID LEVEL RIDGING
FADES TO THE WEST...NOT TOTALLY OUT OF THE PICTURE...BUT DEFINITELY
LESS OF AN INFLUENCE...A COLD FRONT WILL PUSH SOUTH FRIDAY NIGHT
INTO THE COASTAL BEND AND RIO GRANDE PLAINS JUST NORTH OF THE LOCAL
CWA. THE SURFACE BOUNDARY WILL HANG UP AND CONTINUE TO MOVE SLOWLY
SOUTH THROUGH THE WEEKEND...ACTING AS A FOCUS FOR CONVECTION...ALSO
ENHANCED BY MID LEVEL WEAKNESS OVERHEAD...COURTESY OF A LARGE SCALE
TROUGH EXTENDING SOUTHWEST OUT OF THE MISSISSIPPI VALLEY. THAT WILL
BE THE SETUP ENTERING THE LONG TERM. BLENDED POPS ACROSS NORTHERN
SECTIONS TO MARRY UP WITH THE ADJACENT CWA...MAINTAINING A SLIGHT
CHANCE TO CHANCE OF SHOWERS AND THUNDERSTORMS OVERALL. MOISTURE WILL
BE FOCUSED ALONG THE FRONT THROUGH SUNDAY NIGHT...WHEN SLIGHTLY
DRIER AIR FILTERS IN FROM THE NORTH BEHIND THE FRONT. WILL MENTION
ADDITIONAL MID LEVEL ENERGY NOW EVIDENT WEST OF THE RIO GRANDE
PLAINS...WHICH COULD EXACERBATE TSTM CHANCES FRIDAY NIGHT THROUGH
SUNDAY NIGHT FROM LRD NORTH...SOME OF WHICH COULD MOVE SOUTH INTO
THE UPPER VALLEY.

A WEAK FRONTAL BOUNDARY WILL PERSIST ACROSS SOUTH CENTRAL TEXAS
THURSDAY. THE FRONT WILL DRIFT A BIT FARTHER SOUTH ON FRIDAY AND
WILL "HANG UP" ACROSS THE NORTHERN PORTION OF THE CWA ON SATURDAY.
MOISTURE POOLING ALONG THE BOUNDARY...WITH PWAT UP TO TWO INCHES
ON SATURDAY...AND INSTABILITY ALONG IT...WILL INCREASE RAIN
CHANCES LATE FRIDAY THROUGH AROUND MONDAY...BEING MOSTLY DIURNALLY
DRIVEN. MORE SIGNIFICANT CONVECTION COULD DEVELOP AT THE TAIL END
OF THE FRONT OVER THE RIO GRANDE PLAINS AND THE MEXICAN PLATEAU
SATURDAY AND SUNDAY NIGHTS...WITH THE POSSIBILITY OF SOME ACTIVITY
DRIFTING EAST INTO DEEP SOUTH TEXAS AND THE RIO GRANDE VALLEY.
OVERALL HOWEVER...DAYTIME SHOWER AND TSTM ACTIVITY LOOK TO BE
MAINLY ISOLATED TO SCT RIGHT NOW. IN ADDITION TO THE STALLED
FRONT...THE UPSTREAM MID LEVEL RIDGE WILL REMAIN AT BAY OVER THE
SOUTHERN ROCKIES...WITH EVEN SOME SOUTHWEST MONSOONAL INSTABILITY
GETTING INTO THE ACT WITH ENERGY MOVING FROM WEST TO EAST OVER
NORTHERN MEXICO...SUPPORTING THE SATURDAY AND SUNDAY NIGHT
CONVECTION MENTIONED EARLIER.

THERE WILL BE A LITTLE MODERATION IN DAYTIME TEMPERATURES SUNDAY
AND MONDAY DUE TO INCREASED CLOUD COVER AND THE RETREAT OF THE MID
LEVEL RIDGE...LOWERING COLUMN HEIGHTS...BUT DON`T HOLD YOUR BREATH
FOR ANYTHING MUCH BELOW NORMAL. THE RIDGE WILL TRY TO BUILD BACK
OVER THE AREA EARLY NEXT WEEK WITH SOME MID LEVEL DRYING. STILL...
THE MODELS SEEM TO BE IN A GENERAL AGREEMENT IN PLACING THE RGV
AND ALL OF COASTAL TEXAS IN A WEAK TROUGH OR WEAKNESS BETWEEN THE
DESERT SW RIDGE AND THE BERMUDA HIGH IN THE NORTHWEST CARIBBEAN
AND EAST GULF. ENOUGH MOISTURE COULD SUPPORT A SEA BREEZE MONDAY
THROUGH WEDNESDAY BUT LESS LIKELY AFTER THAT AS THE ENVIRONMENT
BECOMES DRIER.

MONDAY THROUGH WEDNESDAY OF NEXT WEEK WILL LIKELY SEE THE RETURN OF
MORE SETTLED CONDITIONS...AS RIDGING FROM THE WEST MAKES A BIT OF A
COMEBACK...OR PERHAPS BETTER PUT WOULD BE THAT THE MS VALLEY TROUGH
FILLS. A SEA BREEZE SHOULD BE POSSIBLE...WITH PWAT VALUES STAYING
ABOVE 1.5 INCHES WITH MODERATE ONSHORE BREEZES.

THE INHERITED FORECAST WAS KEPT MAINLY INTACT. AS MENTIONED...THE
HEAT WILL CONTINUE ON FRIDAY...WITH MID 90S COAST TO 100 OR MORE OUT
WEST...AND TO SOME EXTENT ON SATURDAY...BUT MAYBE LESS HOT SUNDAY
THROUGH EARLY NEXT WEEK BY JUST A COUPLE OF DEGREES. A MIX OF CLOUDS
AND SUN WILL NOT COMPLETELY SHIELD THE SURFACE. LOW TEMPS WILL
CONTINUE TO BE IN THE 70S TO NEAR 80.

MARINE...
NOW THROUGH FRIDAY...BREEZY CONDITIONS ARE EXPECTED TODAY ON THE
LAGUNA MADRE AND HAVE ISSUED A SMALL CRAFT ADVISORY FOR WINDS FOR
THE LAGUNA FROM LATE THIS MORNING THROUGH LATE THIS AFTERNOON.
WINDS WILL BE STRONGER ON THE WESTERN HALF OF THE BAY. TONIGHT
SOUTHEAST WINDS SHOULD BECOME MORE LIGHT MODERATE AS LOW PRESSURE
OVER CENTRAL TEXAS MOVES CLOSER. MODERATE SOUTHEAST WINDS AND
MODERATE SEAS ARE FORECAST FRIDAY.

FRIDAY NIGHT THROUGH MONDAY...A FLAT PRESSURE FIELD OVER THE GULF
WILL PRODUCE LIGHT TO MODERATE SOUTHEAST WINDS AND LOW TO MODERATE
SEAS AT THE BEGINNING OF THE LONG TERM. A COLD FRONT WILL HANG UP
JUST NORTH OF THE AREA FRIDAY NIGHT...WITH ISOLATED TO SCATTERED
SHOWER AND THUNDERSTORM SPILLOVER INTO THE NORTHERN MARINE ZONES
OF THE LOWER TEXAS COAST...AND THEN COVERING ALL OF THE MARINE
AREAS SATURDAY AS THE FRONT PUSHES OFFSHORE AND DISSIPATES...WITH
LIGHT EAST TO SOUTHEAST WINDS PREVAILING. MID LEVEL TROUGHING FROM
THE LOWER MS VALLEY WILL EXTEND SOUTHWEST OVER THE NORTHWEST
GULF...POSSIBLY TRIGGERING CONTINUED CONVECTION SATURDAY INTO
SATURDAY NIGHT OVER THE MARINE AREAS. THIS GENERAL PATTERN WILL
CONTINUE THROUGH MONDAY AND POSSIBLY BEYOND...WITH UNSETTLED
MARINE WEATHER...WHILE WINDS AND SEAS REMAIN BELOW ANY ADVISORY
LEVELS.

FIRE WEATHER...
EXPECT TO CROSS INTO ENHANCED RISK OF WILDFIRE GROWTH AND SPREAD
RANGE THIS AFTERNOON AS SOUTHEAST WINDS INCREASE AND DRY AIR MIXES
DOWN FROM ALOFT. THE FOCUS ZONE TODAY APPEARS TO BE HIDALGO AND
BROOKS COUNTY EAST EXCEPT FOR THE IMMEDIATE COAST WHERE RELATIVE
HUMIDITY VALUES WILL BE TOO HIGH. WILL ISSUE A FIRE DANGER
STATEMENT THIS MORNING HIGHLIGHTING THE THREAT.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  95  80  94  79 /   0  10  10  10
BROWNSVILLE          98  79  95  78 /   0  10  10  10
HARLINGEN           100  78  98  78 /   0  10  20  10
MCALLEN             104  79 100  79 /   0  10  10  10
RIO GRANDE CITY     104  79 101  78 /   0  10  10  30
SOUTH PADRE ISLAND   90  81  89  80 /   0  10  10  10

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT ADVISORY FOR WINDS FROM 11 AM THIS MORNING TO 6 PM
     CDT THIS EVENING FOR GMZ130-132-135.

&&

$$

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