Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 180534
AFDBRO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
1234 AM CDT SAT APR 18 2015

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

&&

.AVIATION...DEEP CONVECTION HAS WOUND DOWN AND NO SIGNIFICANT NEW
ACTIVITY IS ANTICIPATED OVERNIGHT WITH THE AIRMASS STABILIZING. A
FEW SHOWERS AND AREAS OF STRATIFORM PRECIP ARE LIKELY BUT
SIGNIFICANT OPERATIONAL IMPACTS APPEAR UNLIKELY. AN MVFR CIG WILL
IS EXPECTED TO DETERIORATE TO AROUND IFR THROUGH THE NIGHT
TONIGHT. CONVECTION WILL BE POSSIBLE AGAIN TOMORROW ESPECIALLY IN
THE LATE AFTERNOON...MAINLY EAST OF HIGHWAY 281. /68-JGG/

&&

.PREV DISCUSSION... /ISSUED 932 PM CDT FRI APR 17 2015/

DISCUSSION...TORNADO WATCH 70...PREVIOUSLY IN EFFECT FOR ZAPATA
AND JIM HOGG COUNTIES...IS NOW ALSO IN EFFECT FOR BROOKS...STARR
..AND HIDALGO COUNTIES PER DISCUSSION WITH STORM PREDICTION
CENTER AND ONGOING EVOLUTION OF SEVERE THUNDERSTORMS OVER ZAPATA
AND STARR COUNTIES. SHORT TERM PRODUCTS UPDATED.

PREV DISCUSSION... /ISSUED 716 PM CDT FRI APR 17 2015/

DISCUSSION...STORM PREDICTION CENTER HAS DROPPED A TORNADO WATCH
ON ZAPATA AND JIM HOGG COUNTIES OF DEEP SOUTH TEXAS UNTIL 2 AM CDT
SATURDAY MORNING. CURRENT RADAR IMAGERY SHOWS BIG THUNDERSTORMS
FIRING UP OVER NUEVO LEON STATE IN MEXICO AND HEADING TOWARDS
ZAPATA COUNTY AND WFO CRP/S WEBB COUNTY. SHORT TERM PRODUCTS
UPDATED.

PREV DISCUSSION... /ISSUED 651 PM CDT FRI APR 17 2015/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...MID TO HIGH LEVEL CLOUDINESS CONTINUES TO STREAM
OVERHEAD COURTESY OF SOUTHWEST FLOW ALOFT. IN ADDITION...
SOUTHEAST FLOW AT THE SURFACE IS FEEDING LOW TO MID LEVEL
MOISTURE SUPPORTING LOW LEVEL CLOUDS WITH MVFR TO LOW END VFR
CEILINGS ACROSS DEEP SOUTH TEXAS THIS EVENING. MID LEVEL ENERGY
ALONG WITH OUT FLOW BOUNDARIES WILL INCREASE THE POTENTIAL FOR
CONVECTION LATER THIS EVENING ACROSS THE NORTHERN RANCHLANDS.
THERE IS STILL A POTENTIAL FOR THESE STORMS TO DRIFT SOUTH AND
EAST INTO THE RIO GRANDE VALLEY TONIGHT AND PRODUCE STRONG GUSTY
WINDS...FREQUENT LIGHTNING AND HEAVY RAIN. CEILINGS WILL GRADUALLY
LOWER FROM MVFR LATE THIS EVENING TO IFR CLOSER IN THE EARLY
MORNING HOURS WITH THE POTENTIAL OF VCTS/TSRA LATER TONIGHT.
CEILINGS WILL GRADUALLY BEGIN TO INCREASE SATURDAY MORNING WITH
VCSH POSSIBLE THROUGH LATE MORNING.

PREV DISCUSSION... /ISSUED 308 PM CDT FRI APR 17 2015/

SHORT TERM....SHORT TERM /NOW THROUGH SATURDAY NIGHT/...LATEST
SATELLITE AND WATER VAPOR IMAGERY SHOWS THE UPPER LEVEL LOW
SPINNING OVER NM AND SOUTHERN CO AS IT MOVES EAST. MEANWHILE
SUBTROPICAL JET UNDERNEATH THIS SYSTEM IS MOVING ACROSS MX INTO
SOUTH CENTRAL TEXAS THIS AFTERNOON KEEPING THE AREA UNDER
FAVORABLE DIFFLUENT FLOW ALOFT. RICH LOW LEVEL MOISTURE IS IN
PLACE OVER DEEP SOUTH TEXAS WITH LATEST KBRO 12Z SOUNDING SHOWING
PRECIPITABLE VALUES OF 1.94 INCHES WITH A VERY MOIST SOUNDING.
SCATTERED SHOWERS AND THUNDERSTORMS ARE ALREADY DEVELOPING ALONG
THE WEST PORTION OF THIS MOIST AIR MASS. THE LATEST 18Z KBRO
SPECIAL SOUNDING IS SHOWING A CAP WITH THAT SW FLOW ALOFT WITH
STILL SFC BASED CAPE AROUND 3200 J/KG AND PWATS OF 1.88 INCHES.
THIS WILL LIMIT SOME WHAT THE THUNDERSTORMS DEVELOPMENT BUT AS FEW
ISOLATED SHOWERS AND THUNDERSTORMS COULD POSSIBLY BECOME STRONG AS
THE WINDS ALOFT INCREASE PROMOTING THE RISK OF ROTATION IN SOME OF
THE STORMS. THE POTENTIAL IS STILL POSSIBLE FOR HAIL AND STRONG
DAMAGING WINDS. THE HIGHEST POTENTIAL TO SEE SOME STRONG STORMS
REMAIN IN THE EDGE OF THE CWA EXTENDING FROM NORTHERN ZAPATA...JIM
HOGG AND BROOKS. FURTHER SOUTHEAST INTO STARR...HIDALGO...WILLACY
AND CAMERON...THE RISK IS LESS WITH ONE ISOLATED CASE POSSIBLE BUT
NOT AS HIGH OF A POTENTIAL. THE PRECIPITATION AMOUNTS ARE EXPECTED
IN THE HALF TO ONE INCH TOTAL IN THE NEXT 24 HOURS AND AN
ADDITIONAL INCH POSSIBLE WITH THE HEAVIEST STORMS. TIMING FOR THE
NORTHERN COUNTIES WILL BE BETWEEN BETWEEN 4 TO 7 PM AND EVEN LATER
IN THE NIGHT FOR THE RGV. DUE TO THE CLOUD COVER AND EXPECTED
PRECIPITATION TEMPERATURES WILL REMAIN STEADY IN THE MID 70S
ACROSS THE CWA.

TONIGHT AND SATURDAY...THE UPPER LEVEL LOW OVER NM KEEPS ITS
EASTWARD TRAJECTORY WITH THE SUBTROPICAL JET SLIGHTLY WEAKENING.
CONVECTION OVER THE NORTH WILL PROPAGATE SOUTHEAST INTO THE LOWER
VALLEY AS THE NIGHT PROGRESSES. ABUNDANT LOW LEVEL MOISTURE IS
STILL IN PLACE WHICH WILL ALLOW FOR SHOWERS AND THUNDERSTORMS TO
CONTINUE OVERNIGHT. LOW TEMPERATURES WILL BE IN THE LOW 70S.
SECOND ROUND OF CONVECTION DEVELOPS OVER CRP AND MOVES SOUTHEAST
ACROSS THE AREA ESPECIALLY EARLY IN THE MORNING AND EARLY
AFTERNOON. GFS/ECMWF 12Z MODEL RUN ARE SHOWING AN AREA OF DRY AIR
WRAP AROUND THE SWESTERLY FLOW MOVING INTO THE AREA AS DRY LINE IS
PUSH EAST WITH THE UPPER LOW. THIS WILL PROVIDE A BREAK OF
CONVECTION ESPECIALLY LATE AFTERNOON HOURS SATURDAY. AS THE DRY
AIR MOVES INLAND...THERE WILL BE MORE BREAK IN THE CLOUDS IN THE
AFTERNOON WITH TEMPERATURES REACHING THE MID TO LOW 80S ACROSS THE
CWA. BY SATURDAY NIGHT...DRY AIR OVER THE AREA AND THE UPPER LEVEL
LOW FURTHER EAST FROM THE AREA...THE POTENTIAL FOR CONVECTION
DIMINISHES LOWERING FOR THE REMAINDER OF THE NIGHT TO AROUND 20
PERCENT.

LONG TERM.../SUNDAY THROUGH FRIDAY/...ACTIVE WEATHER PATTERN
CONTINUES INTO TUESDAY BEFORE POSSIBLE LIMITED DRIER WEATHER
PATTERN SETS IN MID TO LATE IN THE WORK WEEK. BIGGER THEN EXPECTED
CHANGES FOR SUNDAY THROUGH TUESDAY ARE IN THE OFFERING WITH THE
APPROACH AND PASSAGE OF A MODERATELY STRONG APRIL COLD FRONT.

BIG PICTURE INDICATES THE UPPER LOW OPENING UP AND BECOMING
ABSORBED INTO A LARGER TROUGH MOVING OUT OF CANADA SUNDAY. THIS
SENDS AND COLD FRONT SOUTH INTO OUR REGION SUNDAY NIGHT INTO MONDAY.
MODEL SOUNDINGS INDICATES A SUBSTANTIAL CAP SUNDAY MORNING AND
ERODING THROUGH THE DAY AS A HEAT SPIKE DEVELOPS AS SOUTHWEST WINDS
DOWNSLOPE OFF THE MEXICAN PLATEAU. RAIN CHANCES INITIALLY ARE LIKELY
TO BE LOW THAN INCREASE AS THE FORCING OF THE FRONT INCREASES. GFS
TIMING FOR CONVECTION INITIATION SUNDAY EVENING AND OVERNIGHT WITH
ECMWF LATE SUNDAY AFTERNOON AND EVENING THROUGH THE OVERNIGHT HOURS.
FORECAST INDICATES A CUT BACK ON POPS AND INCREASE TEMPERATURES FOR
THE DAYTIME AND THEN INCREASE THE RAIN CHANCES SUNDAY NIGHT.

GFS/NAM AND ECMWF HAVE THE FRONT PUSHING SOUTH OF REGION WITH A
COOLER AND MOIST NORTHEAST TO EAST FLOW MONDAY. GFS GUIDANCE IS AT
LEAST 15 TO 20 DEGREES COOLER ON MONDAY WITH SLIGHT RECOVERY ON
TUESDAY. THE EASTERLY UPSLOPE CONVERGENT FLOW AND PERSISTENT UPPER
JET ENHANCING LIFT SHOULD KEEP A DECENT CHANCE OF SHOWERS AND
THUNDERSTORMS IN THE PICTURE. THUNDERSTORMS ARE NOT ANTICIPATED TO
BE SEVERE BUT AN ISOLATED STRONG STORM CAN NOT BE RULED OUT WITH
SOME ELEVATED BUT MUCH WEAKER CAPE.

AS WE HEAD INTO TUESDAY AND THE REST OF THE WEEK...THE OLD FRONT
BEGINS TO HEAD NORTH OR DISSIPATE BUT MIGHT TAKE MUCH OF THE DAY.
RAIN CHANCES REMAIN MODERATELY HIGH AS AN UPPER TROUGH APPROACHES O
NW MEXICO. MODEL DIFFERENCES CONTINUE WITH THE EVOLUTION,
PALCEMENT AND MOVEMENT OF THE UPPER TROUGH. GFS IS STRONGER AND
MOVES THE TROUGH INTO THE DESERT SOUTHWEST WHICH WILL STRENGTHEN
OUR SOUTHERLY FLOW AND KEEPS US RELATIVELY DRIER. THE ECMWF KEEP
THE TROUGH AXIS OVER THE PACIFIC COAST WITH A SLOWER TREND OF A
STRONGER SOUTHERLY FLOW. THIS COULD KEEP THE RAIN CHANCES HIGHER.
A BLEND OF THE TWO KEEPS SOME MENTION OF RAIN IN FORECAST BUT THE
TREND IS LOWER. AS FOR TEMPERATURES WITH LOWER RAIN CHANCES
TEMPERATURES SHOULD BE ON THE INCREASE.

MARINE...NOW THROUGH SATURDAY NIGHT...SOUTHEAST WINDS AND
SEAS WILL REMAIN BETWEEN2 TO 4 FEET OR LESS BUT NO SIGNIFICANT
THREAT. HOWEVER...THE MAIN THREAT WILL BE THE POTENTIAL FOR
SHOWERS AND THUNDERSTORMS IN THE EVENING AND OVERNIGHT. STORMS
THAT DO BECOME STRONG CAN PRODUCE HEAVY RAIN...DAMAGING
WINDS...HAIL AND FREQUENT CLOUD TO GROUND LIGHTNING. STAY TUNED
FOR ANY UPCOMING CHANGES WITH THE CONVECTION.

SUNDAY THROUGH WEDNESDAY...MODERATE SOUTHEAST FLOW TO BE
INTERRUPTED MONDAY AND TUESDAY BY A LATE SEASON COLD FRONT. THE
FRONT MOVES THROUGH THE COASTAL WATERS EARLY MONDAY WITH NORTHEAST
FLOW INCREASING. WINDS TO APPROACH SMALL CRAFT ADVISORY CONDITIONS
WITH BUILDING SEAS INTO TUESDAY AS THE PRESSURE GRADIENT REMAINS
MODERATELY STRONG WITH HIGH PRESSURE BUILDING EXPANDING ACROSS THE
NORTHERN GULF. THE RIDGE MOVES EAST MIDDLE OF THE WEEK WITH THE
MODERATE SOUTHEAST FLOW RETURNING. SHOWERS AND THUNDERSTORMS TAKE
A BRIEF REPRIEVE SUNDAY WITH AN INCREASE SUNDAY NIGHT THROUGH
TUESDAY AS THE FRONT MOVES INTO THE REGION.

&&

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

$$

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