Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 240520 AAA
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
1220 AM CDT FRI APR 24 2015

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

.AVIATION...LARGE CLUSTERS OF SHOWERS AND THUNDERSTORMS CONTINUE
TO FIRE OVER NEIGHBORING MEXICO. RECENT TRACKS OF THE CONVECTION
SUGGEST THAT IT WILL MISS THE BRO/HRL AERODROMES...BUT MAY IMPACT
MFE WITHIN THE NEXT COUPLE OF HOURS. OTHERWISE...THE PREVIOUS
ISSUANCE OF TAFS WAS LARGELY RETAINED. TAFS WILL BE CLOSELY
MONITORED THROUGH THE NEXT FEW HOURS DUE TO THE CONVECTION NEARBY.
&&

.PREV DISCUSSION... /ISSUED 1012 PM CDT THU APR 23 2015/

DISCUSSION...WATCHING AN AREA OF SHOWERS AND THUNDERSTORMS ACROSS
THE UPPER VALLEY INTO ZAPATA COUNTY AS WELL AS ISOLATED SHOWERS
POPPING UP ACROSS THE MIDDLE VALLEY AND NORTHERN RANCHLANDS.
ANOTHER COMPLEX IS WELL SOUTH OF THIS AREA IN NEUVO LEON MOVING
NORTHEAST. AREAS OF SHOWERS AND THUNDERSTORMS ARE AIDED BY A UPPER
SPEED MAX AND MUCAPE OF 3500 J/KG AS SAMPLED BY 00Z BRO SOUNDING.

UPDATED THE GRIDS THROUGH 12Z...RAISING POPS ACROSS THE BOARD
WITH 30S IN THE LOWER VALLEY TO 70S OUT WEST WHERE CONVECTION IS
ONGOING. ALSO ADDED PATCHY FOG ALONG THE COAST AND COASTAL WATERS
AS 4-5 STATUTE MILE VISIBILITIES ARE BEING REPORTED IN THE COASTAL
WATERS AND ALSO THROUGH BEACH WEBCAMS. ONLY SLIGHT MASSAGING TO
TEMPERATURE AND WIND GRIDS NEEDED. UPDATE SENT.

PREV DISCUSSION... /ISSUED 636 PM CDT THU APR 23 2015/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...CIGS AND THE THREAT FOR TSRA THE MAIN CHALLENGES THIS
TAF PERIOD.

TAKING A PEAK AT THE 00Z BRO SOUNDING SHOWS LESS MOISTURE BELOW
THE SUBSIDENCE INVERSION AND IS PROBABLY WHY NOT MUCH IN THE WAY
OF MVFR STRATOCU CLOUDS AROUND CURRENTLY AS COMPARED TO THIS TIME
YESTERDAY. THEREFORE WILL DELAY ONSET OF MVFR CIGS AT OUR TAF
SITES TILL 02Z. IFR CIGS ARE LIKELY PER SHORT TERM MODELS AND SREF
PROBABILITIES SO WILL BRING IFR CIGS AT 04Z. IFR CIGS TO LAST
THROUGH MID MORNING THEN LIFT AND SCATTER INTO STRATOCU.

LOW PRESSURE SLOWLY DEEPENS TO OUR WEST WHICH WILL HELP STRENGTHEN
LOW LEVEL WINDS TONIGHT AND LEAD TO GUSTY WINDS FOR FRIDAY.
DIRECTIONS WILL BE PREDOMINATELY FROM THE SOUTHEAST WITH GUSTS TO
20 KNOTS.

LOOKING ON THE RADAR...SCATTERED TO NUMEROUS TSRA HAS DEVELOPED
OVER NORTHERN MEXICO NOW WITH MORE EXPECTED OVERNIGHT AS
DIFFLUENCE INCREASES AND WEAK PERTURBATIONS MOVE THROUGH THE
SOUTHWEST MID/UPPER FLOW. SHORT RANGE MODELS ALSO DEVELOP MORE
CONVECTION LATER THIS EVENING WHICH SWEEPS THROUGH DEEP SOUTH
TEXAS. THE SUBSIDENCE INVERSION AND DRY LOW LEVEL AIR WILL REMAIN
SO CONFIDENCE ISNT GREAT OF REACHING AND IMPACTING THE VALLEY
TERMINALS. IF IT DOES...POSSIBLY BEGINS AFT 03Z UP VALLEY AND
PERHAPS IMPACTING MFE THEN 06-10Z SWEEPING FROM UP VALLEY TO THE
COAST IMPACTING ALL TERMINALS. WILL METWATCH AND AMEND TAFS AS
NEEDED.

PREV DISCUSSION... /ISSUED 252 PM CDT THU APR 23 2015/

SHORT TERM /NOW THROUGH FRIDAY NIGHT/...RADAR IMAGERY BEGINNING TO
SHOW THE FORMING STAGES OF THUNDERSTORMS WELL TO THE SOUTHWEST ON
THE MOUNTAINS IN MEXICO. THIS IS DUE TO THE DAYTIME PEAK HEATING
CONVECTION BEING ENHANCED BY GOOD DIVERGENCE ALOFT AND THE ARRIVAL
OF A SMALL SHORTWAVE. STORM MOTION STILL CURRENTLY AIMING TO THE
NE...WHILE NICE CAPE VALUES BEGINNING TO INCREASE...ESPECIALLY OUT
WEST. STILL CONCERNED ABOUT THE CAPPING INVERSION...WITH H8 TEMPS
STILL 20 TO 22C. THERE WAS SOME CONVECTION LATE LAST NIGHT ACROSS
THE AREA...SO THUNDERSTORM ACTIVITY WILL STILL BE A THREAT EVEN WITH
THE CAP. ANY THUNDERSTORMS THAT DO DEVELOP WILL QUICKLY BECOME
STRONG...POSSIBLY SEVERE. WILL ALSO NEED TO WATCH THE SEABREEZE
MOVING INLAND...AS THIS COULD PROVIDE A SFC BOUNDARY FOR DEVELOPMENT
AND LOCALLY INCREASE SHEAR OF ANY STORMS THAT TRY TO CROSS IT. ANY
STORMS THAT DO DEVELOP WILL HAVE DEEP MOISTURE TO WORK WITH...SO
HEAVY DOWNPOURS WILL BE AN ISSUE.

CONDITIONS WILL RELAX SOME FRIDAY MORNING AS THE MIDLEVEL TROUGH
SWEEPS AWAY FROM TEXAS...WITH LOWERED MIDLEVEL INSTABILITY. DAYTIME
HEATING WILL STILL BRING THE POSSIBILITY OF THUNDERSTORMS ON THE
MOUNTAINS IN MEXICO...BUT WITH A CONTINUED CAPPING INVERSION AND NO
UPPER SUPPORT...THEY WILL HAVE A MUCH HARDER TIME CROSSING THE
RIVER. TEMPERATURES FRIDAY WILL REACH RIGHT AROUND 90 DEGREES.

LONG TERM /SATURDAY THROUGH WEDNESDAY/...THE CWA IS CURRENTLY IN
SPC`S MARGINAL RISK FOR SEVERE TSTM AREA FOR SATURDAY. CONTINUED
SOUTHWEST FLOW ALOFT WILL PROVIDE A MECHANISM FOR MID LEVEL ENERGY
TO DESTABILIZE THE ATMOSPHERE...WHILE ELEVATED SURFACE DEW POINTS
REPRESENTS THE LOW LEVEL FUEL FOR CONVECTIVE DEVELOPMENT. THE MAIN
THREAT WILL LIKLEY BE CONVECTION MOVING IN FROM THE WEST...HAVING
DEVELOPED OVER THE FRONT RANGE OF THE MEXICAN SIERRAS.

WITH ONE SHORTWAVE TROUGH EXITING OVER THE MIDWEST...AND ANOTHER
DIGGING SOUTH ALONG THE WEST COAST...CONDITIONS WILL IMPROVE
SOMEWHAT AS A WEAK INDUCED RIDGE SETS UP OVER THE NORTHWEST GULF. TO
BE SURE...WITH SOUTHWEST FLOW ALOFT STILL PRESENT...THERE WILL
CONTINUE TO BE A LOW END POTENTIAL FOR SOME CONVECTION FROM THE
WEST...BUT AFTER SATURDAY NO MENTION WILL BE CARRIED IN THE FORECAST
GOING INTO SUNDAY. THAT SAID...THE NEXT TROUGH WILL MOVE OVER THE
FOUR CORNERS SATURDAY NIGHT INTO SUNDAY...THOUGH ITS HIGHER LATITUDE
TRAJECTORY WILLCAUSE MORE TROUBLE FOR NORTH CENTRAL AND EAST TEXAS
SUNDAY NIGHT. STILL...WARM SECTOR CONVECTION COULD BECOME STRONG
OVER THE COASTAL BEND AND RIO GRANDE PLAINS SUNDAY NIGHT INTO
MONDAY...WITH SOME ACTIVITY POSSIBLE FOR THE RANCHLANDS AND BRUSH
COUNTRY. LOCALLY...AN INITIAL WIND SHIFT TO NORTHWEST ALONG WITH
DRIER AIR COULD OCCUR AS EARLY AS LATE MONDAY...WHICH WOULD PROVIDE
SOME CLEARING...AND BOTH THE GFS AND ECMWF ARE SIMILAR WITH THE
GENERAL EVOLUTION OF THE SCENARIO...BUT BOTH ALSO BRING THE TRUE
FRONT IN TUESDAY MORNING AS THE UPPER LOW LIFTS NORTHEAST OUT OF
TEXAS.

THUS...ON TUESDAY...WINDS ALOFT SHOULD BE MORE OUT OF THE NORTHWEST
AND CONDITIONS WILL IMPROVE WITH CLEAR SKIES AND MILDER TEMPS. TEMPS
WILL BE NEAR OR EVEN SLIGHTLY BELOW NORMAL TUESDAY THROUGH THURSDAY
AS NEAR CHAMBER OF COMMERCE WEATHER IS EXPECTED.

MARINE...
NOW THROUGH FRIDAY NIGHT...CONSISTENT CONDITIONS WILL CONTINUE AS
SOUTHEAST WINDS REMAIN AROUND 10KTS. THIS WILL CONTINUE TO PRODUCE
GENERALLY 2 TO 4 FOOT SEAS THROUGH FRIDAY NIGHT.

SATURDAY THROUGH MONDAY...A MODERATE PRESSURE GRADIENT OVER THE WEST
GULF WILL GENERATE LIGHT TO MODERATE SOUTHEAST TO SOUTH WINDS AND
LOW TO MODERATE SEAS WITH A SWELL COMPONENT DUE TO THE PERSISTENT
SOUTHEAST FETCH. ISOLATED SHOWERS AND THUNDERSTORMS MAY CONTINUE
FROM THE SHORT TERM INTO SATURDAY...BUT WILL THEN END. AN UPPER LOW
WILL TRACK ACROSS THE SOUTHWEST U.S. FROM WEST TO EAST OVER THE
WEEKEND SETTING UP THE NEXT SYSTEM TO AFFECT DEEP SOUTH TEXAS AND
THE LOWER TEXAS COAST EARLY IN THE WEEK. THE GFS IS FORECASTING AN
INITIAL SHIFT TO MODERATE NORTH WINDS MONDAY AFTN AS A PREFRONTAL
TROUGH MOVES THROUGH THE AREA...WITH THE MAIN FRONT ARRIVING TUESDAY
MORNING. THE ECMWF IS LESS SUCCESSFUL IN SHIFTING WINDS MONDAY...
KEEPING THEM LIGHT ONSHORE...BUT DOES BRING SHOWER AND THUNDERSTORM
CHANCES BACK INTO THE PICTURE...WITH A FRONT ON TUESDAY AS PER THE
GFS. STRONGER NORTHWEST TO NORTH WINDS BEHIND THE FRONT WILL RESULT
IN SMALL CRAFT ADVISORY CONDITIONS ON TUESDAY.
&&

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

$$

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