Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 230553 AAB
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
1253 AM CDT TUE SEP 23 2014

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

&&

.AVIATION...MOSTLY CLEAR SKIES AND LIGHT WINDS PREVAIL ACROSS DEEP
SOUTH TEXAS EARLY THIS MORNING. VFR CONDITIONS WILL CONTINUE ACROSS
AREA THROUGH THE OVERNIGHT HOURS WITH PATCHY FOG EXPECTED TO
DEVELOP AROUND SUNRISE...REDUCING VISIBILITIES TO MVFR TO NEAR IFR
LEVELS BETWEEN 11 TO 14Z. OTHERWISE...VFR CONDITIONS AND LIGHT TO
MODERATE EAST WINDS WILL PREVAIL ACROSS THE REGION FOR THE NEXT 24
HOURS.


&&

.PREV DISCUSSION... /ISSUED 635 PM CDT MON SEP 22 2014/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...SATELLITE IMAGES AND SURFACE OBSERVATIONS INDICATE
MOSTLY CLEAR SKIES ACROSS MOST OF THE CWA EARLY THIS EVENING.
CEILINGS WERE NEAR 9500FT AT KBRO. EXPECT VFR CONDITIONS TO
PREVAIL THE REST OF THE EVENING BEFORE LIGHT WINDS AND RELATIVELY
CLEAR SKIES ALLOW FOG TO DEVELOP LATE TONIGHT INTO EARLY TUESDAY
MORNING. EXPECT MVFR TO NEAR IFR CONDITIONS WITH PATCHY FOG.

PREV DISCUSSION... /ISSUED 341 PM CDT MON SEP 22 2014/
SHORT TERM.../NOW THROUGH TUESDAY NIGHT/...THE SLUG OF MID LEVEL
DRIER AIR OVER MUCH OF EASTERN TEXAS AND WESTERN GULF OF MEXICO IS
FINALLY FILTERING INTO THE RIO GRANDE VALLEY. ANY LINGERING
SHOWERS OVER THE LOWER AND MID VALLEY SHOULD BE SOUTH OF THE
BORDER BEFORE SUNSET AS A STATIONARY FRONT MOVES JUST SOUTH OF THE
RIVER AS HIGH PRESSURE GRADUALLY BUILDS INTO THE NORTHERN GULF.

TONIGHT...A LAYER OF VERY DRY AIR BETWEEN 800-500MB SPREADS OVER THE
REGION TONIGHT BUT LOW LAYER BELOW 850MB STILL REMAIN VERY MOIST
WITH MEAN RH AROUND 90 PERCENT. CONDITIONS LOOK TO BECOME CONDUCIVE
FOR FOG DEVELOPMENT AS WINDS OVERNIGHT BECOME CALM AND TEMPERATURES
COOL OFF ALLOWING FOR BOUNDARY LAYER TO SATURATE. FORECAST MODEL
SOUNDINGS ALSO SUGGEST FOG DEVELOPING OVERNIGHT INDICATING SHALLOW
DENSE SURFACE MOISTURE...STABLE DRY AIR JUST ABOVE A DEVELOPING
INVERSION AND SURFACE MOISTURE REMAINING VERY HIGH DUE TO THE RECENT
RAINS. HOW DENSE THE FOG BECOMES IS UNSURE BUT WITH THE WET
GROUND PATCHES OF DENSE FOG IS PROBABLE. DO NOT ANTICIPATED A DENSE
FOG ADVISORY BUT A FEW HOURS OF GROUND FOG BELOW ONE HALF MILE
ACROSS THE NORTHERN RANCHLANDS AND AROUND HARLINGEN CAN NOT BE RULED
OUT. THE HOURS BETWEEN 4 AND 8 AM WILL BE THE BEST TIMES TO SEE THE
FOG.

TUESDAY AND TUESDAY NIGHT...THE MOISTURE DOES NOT PUSH TO FAR SOUTH
AND A STATIONARY FRONT REMAINS JUST SOUTH OF THE RIVER EARLY
TUESDAY. MODELS CONTINUE TO ADVERTISE A QUICK RETURN OF MOISTURE AS
THE MID LEVEL DRY AIR CONTINUES TO BE SHUNTED TO THE WEST. SURFACE
HIGH PRESSURE MOVES EAST AND EASTERLY WINDS STRENGTHEN AS A WEAK
COASTAL TROUGH DEVELOPS LATE IN THE DAY. THIS COASTAL TROUGH OR THE
STATIONARY BOUNDARY WILL ACT AS A WEAK CONVERGENCE ZONE ONCE THE
DEEPER MOISTURE THAT WILL RESIDE TO OUR SOUTH BEGINS IT TRACK BACK
NORTH. MODELS SUGGEST THAT CONVECTION TO FORM IN THE AFTERNOON WITH
HIGHEST POPS TUESDAY NIGHT OVER THE COASTAL WATERS AND COASTAL
COUNTIES. HAVE KEPT POPS BELOW MODEL CONSENSUS ESPECIALLY TUESDAY
NIGHT. AFTER ANY MORNING FOG SOME BRIEF SUNSHINE BE THE DAILY
CUMULUS CLOUDS DEVELOP WITH THE DAYTIME HEATING. TEMPERATURES TO
START OFF RATHER COMFORTABLE FOR THE LAST DAY OF SUMMER WITH LOW TO
MID 70S THEN AFTERNOON HIGH TO REACH AROUND 90 ACROSS THE BOARD WITH
MID TO UPPER 80S ALONG THE IMMEDIATE COAST LINE.

LONG TERM.../WEDNESDAY THROUGH MONDAY NIGHT/...
A SLOW MOVING UPPER TROUGH OVER THE UPPER MIDWEST WEDNESDAY DIGS
SOUTH ACROSS THE CENTRAL PLAINS WEDNESDAY INTO THURSDAY WHILE THE
CUT-OFF LOW OVER THE EASTERN SEABOARD WEAKENS. SURFACE FLOW WILL
BE DOMINATED BY A BROAD HIGH PRESSURE TOWARDS THE EAST AND WILL
KEEP AN EAST FLOW OVER THE NORTHERN GULF COAST. THIS WILL ALLOW
FOR DEEP MOISTURE OVER THE GULF WATERS TO MIGRATE WEST INTO THE
CWA. THIS WEATHER PATTERN WILL BE IN PLACE FOR MOST OF THE LONG
TERM KEEPING THE POTENTIAL FOR SHOWERS AND THUNDERSTORMS THROUGH
MONDAY NIGHT. WEAK LOW DEVELOPS OVER THE NORTHERN GULF AND IT IS
EXPECTED TO MOVE CLOSER TO THE CWA BY FRIDAY. THIS WILL ALSO HELP
ENHANCE THE SHOWER ACTIVITY FRIDAY THROUGH SATURDAY. THE OVERALL
DEEPER LAYER MOISTURE LEVELS NEVER COMPLETELY DIMINISH OVER THE
RGV THROUGHOUT THE LONGER RANGE PERIOD WITH THE RGV STAYING ON THE
NORTHERN MOST EDGE OF A LARGER AREA OF MOISTURE THAT STAYS POOLED
OVER MUCH OF MEXICO AND THE GULF OF MEXICO. THE CONV POTENTIAL MAY
ALSO BE ENHANCED BY THE PRESENCE OF A PERSISTENT COASTAL SURFACE
TROUGH NEXT THE LOWER TX COASTLINE FOR MUCH OF THIS UPCOMING WORK
WEEK. HIGH TEMPERATURES REMAIN AROUND 90S DEGREES AS THE CLOUD COVER
LIMITS DAYTIME HEATING. LOW TEMPS WILL RANGE BETWEEN LOW TO MID 70S
ACROSS THE CWA THROUGH THE END OF THE WEEK.

MARINE...NOW THROUGH TUESDAY NIGHT...MODERATE TO MODERATELY STRONG
NORTHEAST TO EAST TO PERSIST OVER THE NORTHERN GULF BETWEEN HIGH
PRESSURE OVER THE CENTRAL U.S. AND LOWER PRESSURE OVER THE SOUTHERN
GULF OF MEXICO. MAIN MARINE IMPACT WILL BE A LONG PERIOD EASTERLY
SWELL TRAIN. MARGINAL SMALL CRAFT ADVISORY CONDITIONS MAINLY FOR
SEAS FLOW BUOY 42020 CURRENTLY REPORTING EAST WINDS OF 16 KNOTS WITH
GUSTS NEAR 18 KNOTS WITH SEAS OF 5.9 FEET. THE PRESSURE GRADIENT IS
EXPECTED TO STRENGTHEN LATER TODAY INTO TONIGHT AS HIGH PRESSURE
BUILDS ACROSS THE NORTHERN GULF. EXERCISE CAUTION CONDITIONS WILL
PREVAIL OVER THE LOWER TEXAS GULF WATERS TODAY AND TONIGHT DUE TO
THE INCREASE IN WINDS AND SEAS.

WEDNESDAY THROUGH MONDAY...STRONG HIGH PRESSURE OVER THE
GULF WATERS WILL KEEP AN EAST TO NORTHEAST FLOW ACROSS THE GULF
WATERS. WINDS WILL REMAIN LIGHT TO MODERATE THROUGH THE WEEKEND
WITH SHOWERS AND THUNDERSTORMS DEVELOPING THROUGH THE WEEK. THE
ABUNDANT MOISTURE IN PLACE WILL KEEP CONVECTION DEVELOPMENT
THROUGH THE LONG TERM. SEAS WILL BUILD CLOSE TO SCA FRIDAY.
EXPECT THUNDERSTORMS TO PRODUCE ERRATIC WINDS AND SEAS.

PREV DISCUSSION... /ISSUED 318 PM CDT MON SEP 22 2014/

SHORT TERM.../NOW THROUGH TUESDAY/...BROWNSVILLE RADAR CURRENTLY
SHOWS SCATTERED SHOWERS ACROSS THE SOUTHERN TEXAS COASTAL WATERS
EXTENDING WESTWARD INTO PORTIONS OF THE MID AND LOWER RIO GRANDE
VALLEY. THE 0Z BRO SOUNDING INDICATED PRECIPITABLE WATER VALUES OF
2.22 INCHES.

THE FORECAST IS TRICKY TODAY AS FAR AS POPS GO. MID LEVEL DRIER AIR
SLOWLY BEGINS TO FILTER INTO THE REGION TODAY BUT MODELS CONTINUE TO
DIFFER ON THE TIMING AND HOW FAR SOUTH THE DRIER AIR REACHES.
MET/MAV GUIDANCE ALONG THE WITH ECMWF INDICATE HIGHER POPS THIS
MORNING WITH RAIN CHANCES QUICKLY DECREASING BY THIS AFTERNOON. THIS
IS CERTAINLY POSSIBLE BUT DUE TO MODEL INCONSISTENCIES...CAN NOT
RULE OUT SOME LINGERING SHOWERS THIS AFTERNOON. OTHERWISE...A MIX OF
CLOUDS AND SUN TODAY WITH HIGH TEMPERATURES RANGING FROM THE MID 80S
ALONG THE COAST TO THE MID 90S ACROSS THE WEST.

TONIGHT AND TUESDAY...THE SLIGHTLY DRIER AIRMASS AND MOSTLY CLEAR
SKIES WILL ALLOW OVERNIGHT LOW TEMPERATURES TO DROP AROUND 70
DEGREES ACROSS THE NORTHERN RANCHLANDS WITH TEMPERATURES REMAINING
IN THE MID TO UPPER 70S ELSEWHERE. THE TROPICAL AIRMASS RETURNS TO
THE AREA ON TUESDAY. MODEL GUIDANCE SUGGESTS THE DEVELOPMENT OF
COASTAL SHOWERS BY TUESDAY MORNING. WILL MAINTAIN THE INHERITED
FORECAST OF A SLIGHT CHANCE OF SHOWERS FOR TUESDAY. HIGH
TEMPERATURES ON TUESDAY WILL RANGE FROM THE MID 80S ALONG THE COAST
TO THE LOWER 90S ELSEWHERE UNDER PARTLY CLOUDY SKIES.

LONG TERM...WEDNESDAY THROUGH MONDAY NIGHT/...A SLOW MOVING
UPPER TROUGH OVER THE UPPER MIDWEST WEDNESDAY DIGS SOUTH ACROSS
THE CENTRAL PLAINS WEDNESDAY INTO THURSDAY WHILE THE CUT-OFF LOW
OVER THE EASTERN SEABOARD WEAKENS. SURFACE FLOW WILL BE DOMINATED
BY A BROAD HIGH PRESSURE TOWARDS THE EAST AND WILL KEEP AN EAST
FLOW OVER THE NORTHERN GULF COAST. THIS WILL ALLOW FOR DEEP
MOISTURE OVER THE GULF WATERS TO MIGRATE WEST INTO THE CWA. THIS
WEATHER PATTERN WILL BE IN PLACE FOR MOST OF THE LONG TERM KEEPING
THE POTENTIAL FOR SHOWERS AND THUNDERSTORMS THROUGH MONDAY NIGHT.
WEAK LOW DEVELOPS OVER THE NORTHERN GULF AND IT IS EXPECTED TO
MOVE CLOSER TO THE CWA BY FRIDAY. THIS WILL ALSO HELP ENHANCE THE
SHOWER ACTIVITY FRIDAY THROUGH SATURDAY. THE OVERALL DEEPER LAYER
MOISTURE LEVELS NEVER COMPLETELY DIMINISH OVER THE RGV THROUGHOUT
THE LONGER RANGE PERIOD WITH THE RGV STAYING ON THE NORTHERN MOST
EDGE OF A LARGER AREA OF MOISTURE THAT STAYS POOLED OVER MUCH OF
MEXICO AND THE GULF OF MEXICO. THE CONV POTENTIAL MAY ALSO BE
ENHANCED BY THE PRESENCE OF A PERSISTENT COASTAL SURFACE TROUGH
NEXT THE LOWER TX COASTLINE FOR MUCH OF THIS UPCOMING WORK WEEK.
HIGH TEMPERATURES REMAIN AROUND 90S DEGREES AS THE CLOUD COVER
LIMITS DAYTIME HEATING. LOW TEMPS WILL RANGE BETWEEN LOW TO MID
70S ACROSS THE CWA THROUGH THE END OF THE WEEK.

MARINE...NOW THROUGH TUESDAY...BUOY 42020 CURRENTLY REPORTING EAST
WINDS OF 16 KNOTS WITH GUSTS NEAR 18 KNOTS WITH SEAS OF 5.9 FEET.
THE PRESSURE GRADIENT IS EXPECTED TO STRENGTHEN LATER TODAY INTO
TONIGHT AS HIGH PRESSURE BUILDS ACROSS THE NORTHERN GULF. EXERCISE
CAUTION CONDITIONS WILL PREVAIL OVER THE LOWER TEXAS GULF WATERS
TODAY AND TONIGHT DUE TO THE INCREASE IN WINDS AND SEAS.

WEDNESDAY THROUGH MONDAY...STRONG HIGH PRESSURE OVER THE
GULF WATERS WILL KEEP AN EAST TO NORTHEAST FLOW ACROSS THE GULF
WATERS. WINDS WILL REMAIN LIGHT TO MODERATE THROUGH THE WEEKEND
WITH SHOWERS AND THUNDERSTORMS DEVELOPING THROUGH THE WEEK. THE
ABUNDANT MOISTURE IN PLACE WILL KEEP CONVECTION DEVELOPMENT THROUGH
THE LONG TERM. SEAS WILL BUILD CLOSE TO SCA FRIDAY. EXPECT SHOWERS
AND THUNDERSTORMS TO PRODUCE ERRATIC WINDS AND SEAS.

&&

.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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