Area Forecast Discussion
Issued by NWS Brownsville, TX

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS64 KBRO 200620 AAB
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
120 AM CDT MON APR 20 2015

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

&&

.AVIATION...LATEST SURFACE OBSERVATIONS AND SATELLITE IMAGES
INDICATE PATCHY FOG AND LOW CLOUDS. VISIBILITIES RANGE FROM 3/4SM
AT BRO TO 5SM AT MFE. CEILINGS WERE 200 FEET AT BRO AND PIL TO
AROUND 500 FEET AT HRL/MFE AND EBG. A MIX OF LIFR/IFR CONDITIONS
NOW THROUGH 12Z...WITH VLIFR CONDITIONS POSSIBLE AROUND SUNRISE
BEFORE THE ARRIVAL OF A COLD FRONT. VISIBILITIES EXPECTED TO
IMPROVE AFTER 12Z AS NORTH WINDS INCREASE BEHIND THE FRONT.
LOW CLOUDS WITH IFR TO MVFR CONDITIONS EXPECTED ACROSS VALLEY TAF
SITES THROUGH MUCH OF TODAY...EXCEPT VFR CEILINGS POSSIBLE IN THE
AFTERNOON AT MFE. ISOLATED TO SCATTERED CONVECTION ALSO IS
ANTICIPATED TO DEVELOP ALONG AND BEHIND THE FRONT. WILL MAINTAIN
THE PREVIOUS MENTION OF VCTS LATER THIS MORNING AND ADD VCSH FOR
THE AFTERNOON HOURS.

&&

.PREV DISCUSSION... /ISSUED 627 PM CDT SUN APR 19 2015/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...NO ADJUSTMENTS NEEDED TO THE PREVIOUS SET OF TAFS
EXCEPT TO INITIAL CONDITIONS. PREVIOUS AVIATION DISCUSSION
FOLLOWS:

EXTENSIVE CUMULUS FIELD IS SHOWING SIGNS OF BREAKING UP. THIS
SHOULD ACCELERATE THROUGH THE AFTERNOON AS DAYTIME HEATING
INCREASING THE MIXING OF DRIER AIR TO THE SURFACE. ANY MVFR CIGS
BETWEEN 18-21Z SHOULD BECOME VFR AS SKIES GO SCATTERED. LOW LEVEL
INVERSION STRENGTHENS TONIGHT AND WINDS GO LIGHT AS A COLD FRONT
MOVES INTO SOUTH TEXAS. MVFR TO IFR CEILINGS TO DEVELOP SHORTLY
AFTER SUNSET AND PERSIST THROUGH THE NIGHT. SOME MVFR FOG IS
ANTICIPATED BUT CONFIDENCE IS LOW ON IF FOG LOWERS TO IFR BEFORE
THE FRONT MOVES THROUGH MONDAY MORNING AROUND SUNRISE. LOW CLOUDS
WITH IFR TO MVFR CONDITIONS ARE EXPECTED BEHIND THE FRONT AND
SHOULD PERSIST MUCH OF THE DAY MONDAY. ISOLATED TO SCATTERED
CONVECTION ALSO IS ANTICIPATED TO DEVELOP ALONG AND BEHIND THE
FRONT IMPACTING ANY FLIGHTS IN THE MORNING AND INTO THE AFTERNOON.

PREV DISCUSSION... /ISSUED 251 PM CDT SUN APR 19 2015/

SHORT TERM.../NOW THROUGH MONDAY NIGHT/...
.COOLER AND WETTER MONDAY...

UPDATED FORECAST FOR THIS AFTERNOON HAS ELIMINATED THE MENTION ANY
RAIN/CONVECTION FOR THE AFTERNOON AS THE DRIER SOUTHWEST TO WEST
FLOW BETWEEN 850-700MB IS WARMING UP THIS LAYER PLACING A SLIGHT CAP
OVER THE REGION. AFTERNOON HEATING IS NOT EXPECTED TO BE SUFFICIENT
TO BREAK THE CAP WITH AN INCREASE OF HIGH CLOUDINESS AND A SLOW
EROSION OF THE CU FIELD.

LOOKING AHEAD FOR LATE TONIGHT AND MONDAY...CLOSED LOW OVER THE
CENTRAL PLAINS MERGES WITH A SHARP SHORTWAVE DROPPING OUT OF CANADA
PRODUCING A BROAD LARGE COLD TROUGH OVER MUCH OF THE MIDWEST DIPPING
INTO THE DEEP SOUTH. A COLD FRONT ACROSS NORTH CENTRAL TEXAS GETS A
LITTLE SHOVE AS HIGH PRESSURE BUILDS IN BEHIND THE DEVELOPING
TROUGH. ALL MODELS ARE IN GOOD AGREEMENT PUSHING THE FRONT THROUGH
DEEP SOUTH TEXAS OVERNIGHT AND OFF THE LOWER COAST AROUND OR SHORTLY
AFTER SUNRISE. COOLER AIR AND A MOIST EASTERLY FLOW TO MAKE FOR A
CHALLENGING FORECAST. GFS REMAINS THE COOLEST OF THE 12Z MODEL SUITE
AND THE FORECAST REMAINS ON THE COOLER SIDE OF GUIDANCE WITH
TEMPERATURES REMAINING IN THE 70S.  RAIN CHANCES ALSO GO MUCH HIGHER
WITH BOTH THE GFS AND ECMWF IN THE SAME RANGE OF OF 50 TO 80 PERCENT
BY MONDAY AFTERNOON INTO MON EVENING. SURFACE CONVERGENCE
STRENGTHENS WITH A COASTAL TROUGH DEVELOPING AND SPEED DIVERGENCE
INCREASES THE WITH A 100+ KNOTS 250MB JET STREAMING OVERHEAD. AS FOR
THUNDERSTORMS BEST ELEVATED INSTABILITY IS IN THE MORNING WITHIN THE
FRONTAL BOUNDARY AND THE FRONT WILL ACT AS THE BEST FORCING
MECHANISM OF OUR LOW LEVEL MOISTURE OVER THE LAST SEVERAL DAYS. CAPE
VALUES ARE RATHER HIGH BUT ELEVATED IN THE MORNING AND WEAKEN
CONSIDERABLY THROUGH THE AFTERNOON. GFS KEEPS AT LEAST 50 PERCENT
CHANCE OF THUNDER IN FOR THE DAY THE FORECAST WE WILL MENTION
ISOLATED. THE FRONT PRESSES UP AGAINST THE LEE SIDE OF THE SIERRA
MADRE AND UPSLOPE CONDITIONS TO ENHANCE THE RAINFALL NEAR THE RIO
GRANDE. POPS HAVE BEEN INCREASED ACROSS THE RGV AND THE RIVER
COUNTIES TO LIKELY OR 60 PERCENT BY THE AFTERNOON. QPF VALUES ARE A
MAJOR QUESTION WITH THE GFS INDICATING UPWARDS OF 2 INCHES IN SOME
LOCATIONS. EARLIER WPC COORDINATION HAS PLACE THE HEAVIEST RAINFALL
JUST SOUTH OF THE RIVER BUT IT WONT TAKE MUCH TO HAVE THE FRONTAL
BOUNDARY BACK UP ALONG OR NORTH OF THE RIVER KEEPING THE BEST FOCUS
IN OUR REGION.  THIS WOULD BRING INTO PLAY SOME LOCALIZED FLOODING
BUT HAVE HELD BACK OFF ON THE MENTION OF LOCALLY HEAVY RAINFALL AT
THIS TIME. WILL CONTINUE TO MONITOR FOR ANY SUBTLE CHANGES. PLENTY
OF RAIN IN MARCH AND EARLY APRIL HAS KEPT THE GROUND NEAR SATURATION
AND IT WONT TAKE MUCH OF SOME AREAS TO SEE FLOODING.

LONG TERM.../TUESDAY THROUGH SUNDAY NIGHT/...
AS THE LARGE SCALE TROUGH MOVES FURTHER EAST AT THE BEGINNING OF THE
LONG TERM...RIDGING BEGINS TO BUILD FROM THE WEST AND RETROGRADE THE
FRONTAL BOUNDARY TUESDAY. THE NORTH TO NORTHEAST WINDS SHIFT TOWARDS
THE EAST LIFTING WITH IT A POCKET OF DEEP LAYER MOISTURE. 12Z GFS/NAM
MODEL SOUNDING SHOWS PRECIPITABLE WATER VALUES RISING BETWEEN 1.8 TO
1.9 INCHES INTO TUESDAY. A WEAK COASTAL TROUGH DEVELOPS OVER THE GULF
WATERS ASSOCIATED WITH THIS BOUNDARY INCREASING LOW LEVEL CONVERGENCE
AND A WEAK OVERRUNNING RAIN PATTERN. THE UPPER LEVEL JET ASIDE TO THE
FRONTAL BOUNDARY WILL BE RIGHT OVERHEAD ENHANCING ISOLATED THUNDER.
AS THE COOLER SURFACE AIR SETTLES IN THE INSTABILITY QUICKLY WEAKENS.
THE SOUNDING SHOW VERY SATURATED THROUGH THE COLUMN WHICH DEPICTS A
VERY HEAVY RAIN FORECAST. THE LATEST 12Z ECMWF MODEL SHOWS THIS BROAD
AREA OF QPF MOVING ACROSS THE MID AND LOWER VALLEY ESPECIALLY FAVORING
THE NORTHEAST SECTION OF THE CWA. THE MAIN CONCERNED WITH THIS PATTERN
WILL BE THE POTENTIAL FOR FLOODING IN POOR DRAINAGE AREAS. ASIDE TO THE
FACT THAT MOST OF THE SOIL IN THE CWA IS ALREADY WELL SATURATED CREATING
MORE RUNOFF ISSUES.

TUESDAY NIGHT INTO WEDNESDAY DEEP LAYER MOISTURE WILL BE IN THE PERIPHERY
OF THE BROAD HIGH PRESSURE ACROSS THE SOUTHEAST PLAINS AND LIFT NORTH AND
OUT OF THE AREA DURING THE DAY WEDNESDAY. DUE TO COOLING FROM THE RAINS
THE TEMPERATURES WILL BE BELOW NORMAL. THURSDAY AND THE REMAINDER OF THE
WEEK WILL BE UNDER UPPER LEVEL RIDGE OVERHEAD WHILE ANOTHER LOW PRESSURE
SYSTEM DEVELOPS OVER THE CA COAST. THIS SYSTEM BEGINS TO LIFT NORTHEAST AS
AN OPEN WAVE INCREASING THE SOUTHWESTERLY FLOW ALOFT OF SOUTH TEXAS. AREA
OF DRY AIR ROTATING UNDERNEATH THIS LOW WILL FILTER INTO THE AREA WHILE A
VERY SHALLOW LOW LEVEL MOISTURE PREVAILS SURGING NORTHEAST WITH THE SE GULF
LOW LEVEL FLOW. THE MOISTURE CONTENT WILL BE VERY LIMITED AND SW FLOW WILL
KEEP US UNDER CAP LIMITING THE POTENTIAL FOR ANY RAINFALL. DUE TO ABUNDANCE
SUNSHINE TEMPERATURES WILL BE NEAR NORMAL ACROSS THE CWA. A FEW PERTURBATIONS
WITHIN THE UPPER FLOW WILL MOVE IN THE PERIPHERY OF THE RIDGE AND ENHANCE
AN ISOLATED SHOWER OR THUNDERSTORM WHICH CAN NOT BE RULED OUT AS MOIST
AIR REMAINS TRAP NEAR THE SIERRA MADRE. THIS CONVECTION COULD LINGER
ITS WAY INTO THE WESTERN COUNTY OF THE CWA LATE AFTERNOON AND EVENING
WHICH IS INDICATED WITH LOW POPS IN THE FORECAST THROUGH FRIDAY.

NEXT WEEKEND...AS THE UPPER TROUGH LIFTS NORTHEAST IT BEGINS TO WEAKEN
APPROACHING THE CENTRAL PLAINS. SOME CUT OFF ENERGY REMAINS OVER THE
PACIFIC COAST KEEPING THE SOUTHWESTERLY FLOW ACROSS SOUTH TEXAS. AS
THE FIRST SHORTWAVE MOVES EAST IT PUSHES A FRONT INTO THE AREA. THE
PLUME OF MOISTURE SHIFTS OVER THE CWA INCREASING THE POTENTIAL FOR
A SLIGHT CHANCE OF SHOWERS DEVELOPING. THIS DRY BOUNDARY MOVES
QUICKLY ACROSS THE AREA ALLOWING FOR THE CONVECTION TO DIMINISH
QUICKLY AND CLEARING OUT SUNDAY. TEMPERATURES WILL RANGE BETWEEN
THE MID TO UPPER 80S TOWARDS THE EAST AND CENTRAL WHILE NEAR 90S
TOWARDS THE WESTERN COUNTIES.

MARINE...NOW THROUGH MONDAY...COLD FRONT HAS STRENGTHENED AND WILL
BE MOVING OFFSHORE THE LOWER COAST AROUND OR SHORTLY AFTER SUNRISE
MONDAY. PRESSURE GRADIENT STRENGTHENS THROUGH THE DAY AND NORTHEAST
WINDS TO APPROACH 20 KNOTS OFFSHORE. LOOKING FOR A POSSIBLE SMALL
CRAFT ADVISORY FOR LATE MONDAY MORNING INTO THE AFTERNOON. SEAS TO
RESPOND BUT WILL SLOWER TO RISE WITH PEAK SEAS BY MONDAY SUNSET.
EXERCISE CAUTION IS LIKELY FOR THE LAGUNA AS THE NORTHEAST WINDS
WILL BE JUST SHY OF 20 KNOTS HOWEVER SOME GUSTS OVER 20 KNOTS ARE
NOT OUT OF THE QUESTION. RAIN CHANCES INCREASE BEHIND THE FRONT
ALONG WITH SOME THUNDERSTORMS.

TUESDAY THROUGH SUNDAY/...EASTERLY FLOW WILL BE IN PLACE EARLY IN
THE LONG TERM PERIOD WITH AN AREA OF DEEP LOW LEVEL MOISTURE
POOLED OVER THE GULF AND SOUTH TEXAS THIS WILL ENHANCE HEAVY RAIN
WITH THIS STORMS WITH POTENTIAL FOR LIGHTNING. THEN INTO TUESDAY
EVENING LOW PRESSURE INTERACTING WITH HIGH PRESSURE OVER THE GULF
WATERS WILL INCREASE THE SOUTHEAST WINDS ACROSS THE GULF WATERS BY
WEDNESDAY. SCEC IS POSSIBLE IN THE AFTERNOON BUT QUICKLY DIMINISH
BY THE EVENING. THE WINDS BEGIN TO SHIFT MORE SOUTHERLY INTO
THURSDAY WITH DRIER CONDITIONS EXPECTED. THE GRADIENT STRENGTHEN
ONCE AGAIN BUT WILL BE MORE SOUTHERLY AND IT HAS A POTENTIAL FOR
SCEC ONCE AGAIN IN THE AFTERNOON. THE SAME TREND CONTINUES THROUGH
FRIDAY RELAXING THE GRADIENT INTO SAT AS A FRONT MOVES THROUGH THE
GULF WATERS. A FEW ISOLATED SHOWERS WILL BE POSSIBLE THROUGH THE
PERIOD.

&&

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

$$

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

63


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.