Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 230529 AAB
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
1229 AM CDT SAT MAY 23 2015

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

.AVIATION...SATELLITE IMAGES AND SURFACE OBSERVATIONS INDICATE
MOSTLY HIGH CLOUDS ACROSS THE CWA LATE TONIGHT. EXPECT VFR
CONDITIONS TO PREVAIL THE REST OF TONIGHT INTO EARLY SAT MORNING
EVEN AS LOW TO MID LEVEL MOISTURE INCREASES ACROSS NORTHEAST
MEXICO AND NORTH OF THE CWA. MVFR CONDITIONS MAY DEVELOP LATE SAT
AFTERNOON INTO SAT EVENING AS CONVECTION DEVELOPS ACROSS PORTIONS
OF THE RIO GRANDE VALLEY AND THE NORTHERN RANCHLANDS AHEAD OF A
WEAK 500MB SHORTWAVE TROUGH MOVING ACROSS NORTHEAST MEXICO SAT
AFTERNOON.
&&

.PREV DISCUSSION... /ISSUED 659 PM CDT FRI MAY 22 2015/
DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...SATELLITE IMAGERY AND SURFACE OBSERVATIONS INDICATE A
FEW PASSING LOW CLOUDS ACROSS DEEP SOUTH TEXAS THIS EVENING. LOW
CLOUDS WILL INCREASE LATER THIS EVENING AND OVERNIGHT WITH MVFR
CEILINGS DEVELOPING AFTER 06Z. SOUTHEAST WINDS AROUND 15 KNOTS THIS
EVENING WILL DIMINISH TO BETWEEN 6 TO 11 KNOTS TONIGHT. SOUTHEAST
WINDS WILL BEGIN TO INCREASE AROUND 14Z AS THE PRESSURE GRADIENT
TIGHTENS ALONG THE LOWER TEXAS COAST. DAYTIME HEATING ALONG WITH
BREEZY WINDS WILL ALLOW MVFR CEILINGS TO QUICKLY MIX OUT WITH VFR
CONDITIONS EXPECTED AT ALL TAF SITES AFTER 14Z.

PREV DISCUSSION... /ISSUED 351 PM CDT FRI MAY 22 2015/

SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/...WILL SEE A FEW
RESIDUAL SHOWERS OVER THE AREA THROUGH THIS EVENING...BUT THE REST
OF THE NIGHT SHOULD REMAIN TRANQUIL...THOUGH THUNDERSTORMS MAY  STAY
ALIVE OVER THE SIERRA MADRES TO THE WEST FOR PART OF THE NIGHT. LOW
TEMPS WILL BE IN THE MID TO UPPER 70S.

LIGHT TO MODERATE SOUTHEAST WINDS WILL CONTINUE ON SATURDAY UNDER A
MIX OF CLOUDS AND SUN...WITH HIGH TEMPS IN THE MID 80S TO NEAR 90.
MOISTURE MOVING UP THE COAST FROM THE SOUTH WILL RESULT IN SCATTERED
SHOWERS OVER THE NEARSHORE AND THE COASTAL COUNTIES. SHOULD SEE SOME
CONVECTION PERCOLATING INLAND OVER THE RIO GRANDE PLAINS AS A MID
LEVEL LOW EJECTS FROM SOUTHERN CALIFORNIA TO THE FOUR CORNERS AND
THEN THE HIGH PLAINS.

CONVECTIVE CHANCES WILL INCREASE SATURDAY NIGHT THROUGH SUNDAY.
STRONG CONVECTION WILL BE FAVORED OVER THE UPPER VALLEY SATURDAY
NIGHT AS AMPLE MOISTURE FEEDS INTO LARGE SCALE FORCING DUE TO A MID
LEVEL TROUGH AXIS APPROACHING NORTHWEST TX AND AS A LINE OF ENERGY
ALOFT MOVES OUT OF MEXICO AND OVER DEEP SOUTH TEXAS. UPSTREAM
SHOWERS AND THUNDERSTORMS COULD CONTINUE TO MOVE EAST OVER ALL OF
DEEP SOUTH TEXAS LATER SATURDAY NIGHT AND INTO SUNDAY. THE OUTLOOK
FOR SEVERE WEATHER PLACES THE CWA IN A SLIGHT RISK ON SUNDAY. STRONG
WINDS...HAIL AND AN ISOLATED TORNADO WILL BE THE MAIN THREATS. FLASH
FLOODING COULD BE A THREAT DUE TO RESIDUAL GROUND SATURATION FROM
PREVIOUS RAINS. A FLASH FLOOD WATCH MAY BE ISSUED IF CONFIDENCE IN
EXCESSIVE RAIN INCREASES.

LONG TERM /SUNDAY THROUGH FRIDAY/...A SERIES OF STRONG AND DEEP
500 MB TROUGHS WILL DIG ACROSS THE SOUTH CENTRAL PLAINS STATES ON
SUN AND MON. THE PASSAGE OF THESE 500 MB FEATURES WILL PROVIDE
PLENTY OF MID AND UPPER LEVEL SUPPORT FOR CONV ACROSS MOST OF TX.
DEEPER LAYER MOISTURE WILL POOL AHEAD OF THESE TROUGHS PROVIDING
PLENTY OF ELEVATED CAPE AND PWAT VALUES ACROSS THE STATE. THE BIG
QUESTION IS HOW FAR SOUTH THE BETTER INSTABILITY AND MOISTURE
VALUES WILL REACH. THE ECMWF SHOWS BETTER MOISTURE ADVECTION OVER
DEEP SOUTH TX VERSUS THE GFS WHICH KEEPS MOST OF THE DEEPER LAYER
MOISTURE POOLED FURTHER TO THE NORTH OVER CENTRAL AND SOUTH
CENTRAL TX. EXPECT THE MOST LIKELY SCENARIO IS THAT MORE
WIDESPREAD CONV MAY SKIRT THE THE NORTHERN COUNTIES OF THE CWA
WITH MORE SCT CONV MAKING ITS WAY INTO THE RGV ON SUN AND MON.
MUCH OF THE POTENTIAL CONV MAY LIKELY BE DRIVEN BY MESOSCALE
FEATURES WHICH MAY BE SOMEWHAT DIFFICULT TO ANTICIPATE AT THIS
TIME. SO WILL GO WITH A GENERAL MODEL BLEND OF POPS FOR SUN AND
MON. AFTER THE 500 MB TROUGHS CLEAR THE REGION MON NIGHT INTO
EARLY TUES EXPECT THE CONV POTENTIAL TO DIMINISH SOMEWHAT LATER IN
THE FORECAST PERIOD AS DRIER AND MORE STABLE AIR STARTS ADVECTING
INTO THE REGION AT THE MID AND UPPER LEVELS OF THE ATMS THROUGH
MIDWEEK. AT THIS POINT IN TIME AM NOT CONFIDENT ENOUGH THAT THE
INCREASING SUBSIDENT FLOW PATTERN WILL TOTALLY ELIMINATE THE CONV
POTENTIAL. WILL MAINTAIN SOME MENTION OF SLGT CHC POPS LATE IN THE
FORECAST PERIOD DUE MAINLY TO DIURNAL/SEA BREEZE EFFECTS.

SPC ALSO PLACES DEEP SOUTH TX IN THE SLGT RISK FOR SVR WX ON DAY
3 MAINLY DUE TO THE CLOSER PROXIMITY OF THE 500 MB TROUGHS TO OUR
NORTH AND THE PRESENCE OF GOOD TROPICAL MOISTURE/INSTABILITY OVER
THE REGION.

OVERALL FORECAST TEMP TRENDS WILL BE LINKED PRETTY CLOSELY TO THE
FORECAST POPS. THE ECMWF TEMPS ARE A LITTLE COOLER IN THE LONGER
RANGE PERIOD VERSUS THE GFS MEX NUMBERS. WILL LEAN A LITTLE MORE
TOWARDS THE COOLER ECMWF TEMPS SINCE WE ARE GOING A BIT HIGHER FOR
POPS MAINLY FOR SAT AND SUN. LATER IN THE LONGER RANGE PERIOD WILL
GO CLOSER TO A 50/50 MODEL BLEND OF THE ECMWF/GFS NUMBERS.

THE GFS AND ECMWF MODELS ARE IN BETTER AGREEMENT TODAY IN THE
OVERALL PLACEMENT AND AMPLITUDE OF THE 500 MB FEATURES THROUGH
DAY 7. THE BIGGEST DIFFERENCES BETWEEN THE MODELS THROUGH DAY 7 SHOW
UP IN THE OVERALL MOISTURE FIELDS MENTIONED EARLIER IN THE LONGER
RANGE DISCUSSION. THIS FACTOR WILL HOLD MY FORECAST CONFIDENCE
LEVEL DOWN TO AVERAGE FOR THIS PERIOD FOR MAINLY FOR POPS.

MARINE /TONIGHT THROUGH SATURDAY NIGHT/...SMALL CRAFT EXERCISE
CAUTION TO LOW END SMALL CRAFT ADVISORY CONDITIONS WILL DEVELOP ON
THE GULF THIS WEEKEND AS THE GRADIENT TIGHTENS BETWEEN GULF HIGH
PRESSURE AND LOWER PRESSURE OVER THE SOUTHERN HIGH PLAINS AND WEST
TEXAS.

SUNDAY THROUGH WEDNESDAY...THE COMBINATION OF SURFACE RIDGING OVER
THE GULF OF MEX AND THE SURFACE LOW PRESSURE SYSTEM EXPECTED TO
SPIN UP OVER THE CENTRAL PLAINS STATES LATER THIS WEEKEND INTO
EARLY NEXT WEEK WILL TIGHTEN UP THE PGF. THIS WILL LIKELY KEEP THE
BAY AND GULF CONDITIONS CLOSE TO SCA LEVELS THROUGH AT LEAST THE
MEMORIAL DAY HOLIDAY. THE PGF WILL THEN WEAKEN LATER NEXT WEEK
WHICH WILL ALLOW FOR A LITTLE WEAKER SURFACE FLOW AND SLIGHTLY
LOWER SEAS.

HYDROLOGY...RECENT WATER RELEASES FROM THE EL CUCHILLO AND MARTE
R. GOMEZ RESERVOIRS ON THE MEXICAN SIDE OF THE RIO GRANDE WILL
RESULT IN HIGHER THAN NORMAL FLOWS ON THE SOUTHERN END OF THE RIO
GRANDE. CURRENTLY THE RIVER STAGE AT THE SAN BENITO GAUGE ON THE
RIO GRANDE IS EXPECTED TO RISE STEADILY OVER THE NEXT SEVERAL
DAYS. THE SAN BENITO GAUGE IS EXPECTED TO CREST NEAR 46.9 FEET ON
MONDAY. FLOOD STAGE AT THE SAN BENITO GAUGE IS 55.0 FEET. NO
FLOODING IS EXPECTED. THE LATEST RIVER STAGE AND FORECAST
INFORMATION CAN BE FOUND ON OUR OFFICE WEB PAGE AT
WWW.WEATHER.GOV/RGV ON THE RIVERS/LAKES SECTION.
&&

.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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