Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 202348
AFDBRO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
648 PM CDT SAT SEP 20 2014

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

&&

.AVIATION...SHRA AND TSRA WINDING DOWN AND EXPECTED TO CONTINUE
OVER THE NEXT FEW HOURS. REMANENT BOUNDARIES ACROSS THE MIDDLE AND
LOWER VALLEY SO KEPT VCSH THROUGH THE FIRST TWO HOURS OF THE TAF.
VFR EXPECTED AFT 02Z BUT BRIEF PERIODS OF MVFR 08-12Z CANNOT BE
RULED OUT ESPECIALLY WHERE RAINFALL WAS RECEIVED. SHRA EXPECTED TO
DEVELOP INTO THE LOWER VALLEY BY DAYBREAK WITH TSRA AFFECTING ALL
TERMINALS IN THE AFTERNOON.

&&

.PREV DISCUSSION... /ISSUED 254 PM CDT SAT SEP 20 2014/

SHORT TERM /NOW THROUGH SUNDAY NIGHT/...
THE REMNANTS OF ODILE IS CIRCULATING AROUND THE PERIPHERY OF THE
HIGH PRESSURE ACROSS THE DESERT SOUTHWEST AND HAS MOVE INTO W AND
SOUTH TX TODAY. THIS WILL CONTINUE TO FAVOR CONVECTION THROUGH MOST
OF THE SHORT TERM PERIOD. THE SOUTHEAST TO EAST FLOW IS MAINTAINING
VERY FAVORABLE MOIST ENVIRONMENT OVER THE CWA WITH PRECIP WATER OF
2.3 INCHES NOTED IN THE KBRO 12Z SOUNDING AND 1000 TO 500 RH OF 80
TO 70 PERCENT ACROSS THE AREA. THIS DEEP MOISTURE WILL SUPPORT FOR
ISOLATED TO SCATTERED DOWNPOURS PRODUCING HEAVY RAIN WITH RAINFALL
ACCUMULATIONS BETWEEN 2 TO 3 INCHES. A WEAK SEA BREEZE HAS ALSO
DEVELOP ALONG THE COAST ENHANCING MORE CONVECTION ALONG THE COASTAL
COUNTIES. THE STRONGER STORMS ARE REMAINING CLOSER TO THE RIVER SO
DECIDED TO ALSO INCLUDE INLAND WILLACY TO THE FLASH FLOOD WATCH AND
TO EXTEND THE WATCH THROUGH 7 PM CDT AS THE TREND IN THE MODELS SHOW
MORE DEVELOPMENT THROUGH THIS AFTERNOON.

TONIGHT...THE EASTERLY FLOW WILL CONTINUE ACROSS THE CWA SHIFTING
THE DEEP LAYER OF MOISTURE MORE WESTWARD. STILL MOST OF THE CWA WILL
SEE ISOLATED TO SCATTERED SHOWERS OVERNIGHT BUT INCREASE TO 50
PERCENT TOWARDS THE WESTERN COUNTIES. A SMALL BREAK IS EXPECTED AFTER
MIDNIGHT WITH LOSS OF DAYTIME HEATING BUT CONVECTION WILL INITIATE
BACK IN THE EARLY MORNING HOURS ON SUNDAY.

THIS PATTERN CONTINUES THROUGH SUNDAY WITH HIGH PRESSURE ALOFT
SLIGHTLY SHIFTING WEST AND MOVING THE DEEP MOISTURE TOWARDS THE WEST.
THE CHANCES OF RAIN REMAIN FAVORING THE COUNTIES ALONG THE TX
BORDER. DRY AIR IN THE MID LEVEL MOVES INTO THE CWA WITH A MORE
NORTHEAST FLOW BY THE END OF THE SHORT TERM FORECAST. THIS WILL
ALLOW FOR THE CHANCES TO DIMINISH COMPLETELY. AT THIS TIME...THE
DRY AIR WILL BEGIN TO MAKES ITS WAY INTO THE CWA BY THE END OF THE
SHORT TERM FORECAST.

LONG TERM /MONDAY THROUGH SATURDAY/...LONG TERM FORECAST WILL BE
TRENDING WETTER WITH PLENTY OF UNCERTAINTY. DEEP TROUGH MOVING
ACROSS THE MIDWEST AND NORTHEAST COAST TO PUSH A FRONT TO THE
NORTHWEST GULF MONDAY. THE FRONT GRADUALLY PUSHES SOUTH AS BROAD
SURFACE HIGH PRESSURE BUILDS INTO THE GULF SOUTH STATES AND PULLS
UP STATIONARY SIMILAR TO LAST WEEKS FRONT. DRIER AIR PUSHES SOUTHWEST
BUT IT IS UNCERTAINTY HOW MUCH WORKS ITS WAY INTO OUR CWA. MODELS
IN SOME AGREEMENT MAINTAIN A SHARP DISCONTINUITY BETWEEN THE DRIER
AIR AND TROPICAL AIRMASS THAT IS OVER THE REGION CURRENTLY. THIS
BOUNDARY LOOKS TO CUT THE CWA IN HALF MONDAY WITH RAIN CHANCES
CONTINUING ACROSS THE RIO GRANDE VALLEY AND DRIER CONDITIONS FOR
THE NORTHERN RANCH LANDS. FORECAST REFLECTS THIS THINKING NOW
ADDING 20-30 PERCENT POPS ACROSS THE SOUTH.

THROUGH THE REMAINDER OF THE GFS...ECMWF AND WPC MAINTAIN THE IDENTITY
OF THE STATIONARY FRONT OVER THE NORTHWEST GULF WITH DEEP EASTERLY
FLOW TRAVERSING THE ENTIRE NORTHERN GULF. BROAD CYCLONIC FLOW AND
AN INCREASE OF MOISTURE THROUGH THE WEEK TO KEEP RAIN CHANCES
ALIVE FOR THE FORESEEABLE FUTURE. MODELS ARE IN GENERAL AGREEMENT
WITH THE PATTERN BUT DIFFER IN TIMING AND INTENSITY AND COVERAGE
OF RAIN CHANCES. CENTRAL PLAINS TROUGH TUESDAY AND WEDNESDAY LOOKS
TO BE PLACED TO FAR NORTH TO HAVE MUCH INFLUENCE ON OUR WEATHER AND
THE SOUTHWEST FLOW AT 850-700MB THAT WAS INDICATING IN PREVIOUS
RUNS HAS BACKED OFF AT TIME TIME. WEATHER PATTERN LOOKS MORE
TROPICAL AS THE JET STREAM RETREATS NORTHWARD AND THE GULF WILL BE
UNDER THE INFLUENCE OF DEEP EASTERLIES. BY THE END OF THE
FORECAST PERIOD A WEAK WAVE FORMS ALONG THE STATIONARY FRONT. GFS
IS SOMEWHAT SUBDUE WITH THIS WAVE WHILE THE ECMWF GOES HOG WILD
DEVELOPING A DEEP SURFACE LOW OVER THE NORTHWEST GULF. HAVE GONE
MORE CONSERVATIVE LEANING WITH THE GFS. TEMPERATURES WILL BE
DEPENDENT ON THE RAINFALL AND WILL LIKELY BE ON THE LOWER END OF
GUIDANCE WITH THE INCREASE OF MOISTURE.

MARINE...NOW THROUGH SUNDAY NIGHT...BROAD HIGH PRESSURE OVER THE
GULF WILL KEEP A LIGHT TO MODERATE EASTERLY FLOW ONSHORE THROUGH THE
SHORT TERM FORECAST. THE WINDS WILL REMAIN LIGHT KEEPING SEAS AROUND
2 TO 3 FEET OR LESS. NO SMALL CRAFT ADVISORY AT THIS TIME. THE MAIN
IMPACT WILL BE THE SHOWER ACTIVITY WHICH WILL CONTINUE THROUGH THE
PERIOD AS THERE IS ABUNDANT MOISTURE IN THE AREA. THIS ACTIVITY IS
PRODUCING VERY HEAVY DOWNPOURS AND OCCASIONAL LIGHTNING. EXPECT A
SLIGHTLY NE FLOW EARLY SUNDAY AS DRY AIR FILTERS INTO THE AREA
DIMINISHING THE CHANCE OF RAIN ACROSS THE CWA.

MONDAY THROUGH THURSDAY...MODERATE EASTERLY WINDS ARE FORECAST
MONDAY THROUGH THURSDAY. WIND SPEEDS MAY EXCEED EXERCISE CAUTION
LEVELS AT TIMES BUT A GENERAL MODERATE EAST FLOW WILL PERSIST.
SEAS WILL BECOME MODERATE WITH LONGER PERIOD SWELL DEVELOPING
FROM A LONG FETCH OF EASTERLY WINDS ACROSS THE WESTERN AND CENTRAL
GULF OF MEXICO...PERSISTING THROUGH THURSDAY SEAS MAY EVENTUALLY
BUILD HIGHER THEN CURRENT FORECAST. SHOWER AND THUNDERSTORMS
ACTIVITY IS EXPECTED EACH DAY WITH TUESDAY THROUGH THURSDAY HAVING
THE BEST CHANCES.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...FLASH FLOOD WATCH UNTIL 7 PM CDT THIS EVENING FOR TXZ248-252>255.

GM...NONE.
&&

$$

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

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