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 250601
AFDBRO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
101 AM CDT SAT APR 25 2015

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

&&

.AVIATION...STRONG TO SEVERE CONVECTION HAS MOVED NORTHEAST INTO
THE GULF WATERS AT THIS TIME. THERE IS AN AREA OF SCATTERED
SHOWERS AND THUNDERSTORMS DEVELOPING FROM HARLINGEN DOWN TO
BROWNSVILLE. THE CONVECTION WILL REMAIN FOR THE NEXT FEW HOURS
REDUCING VIS WITH THE HEAVY RAIN. DUE TO THE ABUNDANCE OF MOISTURE
CEILINGS WILL LOWER TO IFR IN THE EARLY MORNING HOURS. THE
CEILINGS WILL BEGIN TO IMPROVE BY MID DAY WITH HZ STILL LINGER
THROUGH THE DAY AS THE AGRICULTURAL BURNING IN MEXICO CONTINUES
WITH A MODERATE AIR QUALITY THROUGH THE DAY.

&&

.PREV DISCUSSION... /ISSUED 936 PM CDT FRI APR 24 2015/

DISCUSSION...SUPERCELL/MULTICELL CLUSTER ABOUT 40 MILES SOUTH OF
THE RIVER CONTINUES TO MOVE SLOWLY NORTHEASTWARD IN THE GENERAL
DIRECTION OF HIDALGO COUNTY. BROWNSVILLE SOUNDING SHOWS A STRONG
CAP BUT INCREASING SPEED DIVERGENCE APPEARS TO BE HOLDING THE
AIRMASS IN PLACE. WITH THE COMPLEX ADVECTION/PROPAGATION ISSUES OF
THIS COMPLEX AND THE INCREASINGLY STABLE AIRMASS IT WILL ENCOUNTER
AS IT MOVES EAST STILL NOT ENTIRELY CERTAIN IT WILL HOLD
TOGETHER...BUT TRENDS HAVE HELD WELL ENOUGH TO INCLUDE HIDALGO
COUNTY IN THE SEVERE THUNDERSTORM WATCH UNTIL 2 AM. LARGE
HAIL/DAMAGING WIND/FLASH FLOODING WILL ALL BE A RISK IF THE
CLUSTER HOLDS TOGETHER IN ITS CURRENT FORM AS IT CROSSES THE
RIVER. /68-JGG/

PREV DISCUSSION... /ISSUED 819 PM CDT FRI APR 24 2015/

DISCUSSION...INITIAL STORM CLUSTER THAT HAS PUSHED INTO ZAPATA
COUNTY APPEARS TO NOT QUITE BE UTILIZING THE FULL INSTABILITY THAT
IS PRESENT THROUGH THE COLUMN AND HAS CONTINUED TO STRUGGLE AS IT
CROSSES THE RIVER. THE LOW CONVERGENCE INVOF THE CELL WILL BE A
FOCUS FOR CONTINUED DEVELOPMENT BUT MAY STRUGGLE AGAINST CAPPING
THAT APPEARS TO INCREASE AS YOU MOVE FROM WEST TO EAST IN THE CWA.

IN HOUSE LAPS/RAP13 SEEM TO HAVE A GOOD HANDLE ON OUR CURRENT
THERMODYNAMIC ENVIRONMENT WHEN COUPLED WITH THE 00Z BROWNSVILLE
SOUNDING. VERY STRONG CAPPING IS EVIDENT ON THE SOUNDING THAT GETS
A LITTLE LESS AS YOU MOVE WESTWARD. THE CAPPING IS BELOW
PARTICULARLY STEEP MID LEVEL LAPSE RATES OF AROUND 8 DEGREES C/KM
SO IF AN UPDRAFT CAN GET INTO THAT LAYER IT COULD BE QUITE
INTENSE.

WATER VAPOR/GFS UPPER AIR ANALYSIS SUGGEST AN INCREASE IN UPPER
DIVERGENCE OVER THE NEXT 3 TO 4 HOURS WHICH WILL INCREASE LOW
LEVEL CONVERGENCE AND WORK ON THE CAP A BIT. RAP13 SUGGESTS IT
WILL BE COMPLETELY LIFTED OUT ALTHOUGH THAT SEEMS UNLIKELY GIVEN
THE SOMEWHAT MODEST AMOUNT OF LIFT THAT WILL BE PRODUCED.

SATELLITE/RADAR TRENDS DO HOWEVER SHOW A LITTLE STRONGER LINE OF
CONVECTION ABOUT 120 MILES WEST OF BROWNSVILLE WITH INCREASED
LIGHTNING ACTIVITY OVER THE LAST 15 TO 30 MINUTES. IF THAT AREA WERE
TO HOLD TOGETHER WOULD BE COLLOCATED WITH IMPROVED LARGE SCALE
ASCENT UPON ARRIVAL AND WOULD LIKELY STILL HAVE A VERY UNSTABLE
BOUNDARY LAYER TO WORK WITH SO WILL KEEP THE GUARD UP FOR THE NEXT
FEW HOURS. /68-JGG/

PREV DISCUSSION... /ISSUED 701 PM CDT FRI APR 24 2015/

DISCUSSION...ALL PRODUCTS UPDATED FOR SVR WATCH 104. CURRENTLY
WATCHING THE LONE SUPERCELL CANDIDATE ABOUT 40 MILES SOUTHWEST OF
FALCON LAKE WITH LESS INTENSE CONVECTION BEHIND IT. ATMOSPHERE
REMAINS ESPECIALLY UNSTABLE WITH GOOD SHEAR SO LIKELY THAT
CELL...PERHAPS WITH A FEW ADJACENT STRONG/SEVERE CELLS WILL BEGIN
TO MARCH INTO THE AREA BY ABOUT 8 PM. LOW LAYER SHEAR IS NOT
ESPECIALLY FAVORABLE FOR STRONG/LONG TRACK TORNADOES BUT THE
SUPERCELLULAR NATURE OF THE CONVECTION MAKES A TORNADO OR TWO AT
LEAST A POSSIBILITY THROUGH THE EARLY EVENING. /68-JGG/

PREV DISCUSSION... /ISSUED 641 PM CDT FRI APR 24 2015/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...CONDITIONAL CONVECTIVE THREAT WILL BE THE HEADLINE IN
THE NEXT FEW HOURS. STRONG TO SEVERE CONVECTION IS ATTEMPTING TO
FIRE OVER MEXICO AND THE ENVIRONMENT IS FAVORABLE FOR STRONG TO
SEVERE STORMS IF THEY ARE ABLE TO INITIATE AND SUSTAIN AND MAY
UPSCALE INTO A RELATIVELY LARGE COMPLEX IN THE VERY HUMID/UNSTABLE
ENVIRONMENT. OTHERWISE PREVAILING MVFR IS EXPECTED TO DETERIORATE
TO IFR BY A LITTLE BEFORE SUNRISE. /68-JGG/

PREV DISCUSSION... /ISSUED 529 PM CDT FRI APR 24 2015/

DISCUSSION...CONTINUING TO MONITOR SVR WX THREAT CLOSELY THIS
EVENING. 22Z MODIFIED LAPS/RAP SOUNDINGS YIELD EXTREME INSTABILITY
WITH EVEN 100MB MLCAPE VALUES OF 3000 TO 3500 J/KG WITH SURFACE
DEWPOINTS IN THE UPPER 70S. DEEP LAYER SHEAR IS ALSO FAVORABLE WITH
LOW LAYER SHEAR THAT IS WEAK...BUT VEERS WITH HEIGHT. A STURDY CAP
REMAINS IN PLACE OVER THE AREA...REINFORCED BY STRONG SOUTHWESTERLY
WINDS ALOFT...BUT SHOULD BE THIN ENOUGH TO ALLOW FOR CONVECTION IF
SOME MID LEVEL ASCENT CAN GET GOING. AN AREA OF FAVORABLE SPEED
SHEAR IS APPROACHING FROM MEXICO AT THE SOUTH END OF A BROADER JET
MAX THAT IS FOCUSED OVER TEXAS...AND THAT MAY BE SUFFICIENT TO
INITIATE MORE CONVECTION IN THE IMMEDIATE LEE OF THE SIERRA MADRE
MOUNTAINS THIS AFTERNOON. HRRR/RAP/NAM SUPPORT SCATTERED CELLS
UPSCALING INTO AN MCS/LEWP OVER THE NEXT FEW HOURS AND MOVING ACROSS
THE AREA. THE END OF DAYTIME HEATING SHOULD LIMIT THE SEVERE WEATHER
RISK EASTWARD SOMEWHAT BUT IT IS DIFFICULT TO ESTIMATE IF IT WILL BE
QUICK ENOUGH TO EXCLUDE SOME OR ALL OF THE RGV METRO AREAS IF
CONVECTION INITIATES. IR/RADAR/LIGHTNING TRENDS IN THE AREA ARE
UP...BUT YET TO BE EXPLOSIVE. SPC SWOMCD PROVIDES FURTHER DETAIL ON
OUR NEAR TERM CONVECTIVE SITUATION.

UPDATED GRIDS TO INCLUDE SEVERE WORDING OVER A LARGER PORTION OF
THE AREA AND WILL BE BEEFING UP THE HWO SLIGHTLY IN THE NEXT FEW
MINUTES. /68-JGG/

PREV DISCUSSION... /ISSUED 255 PM CDT FRI APR 24 2015/

SHORT TERM /NOW THROUGH SATURDAY NIGHT/...H5 TROUGH PROGRESSING
NEWD THROUGH NM CURRENTLY...WITH STRONG MIDLEVEL FLOW WRAPPING
AROUND IT OVERHEAD. INSTABILITY ALOFT IS PEAKING THIS EVENING...
WITH DECENT CAPE VALUES STILL FORECAST ESPECIALLY OUT WEST.
MRNG BRO SOUNDING STILL SHOWED SIGNIFICANT CAPPING INVERSION...
BUT MORE REPRESENTATIVE INLAND SOUNDING FROM DRT SHOWED MINIMAL
CAP AND LOWER CONVECTIVE TEMPERATURE. GOOD CU BUBBLING NOTED TO
THE SOUTHWEST IN MAIN THREAT AREA...SO GOOD CHANCES FOR TSTMS
STILL REMAINS IN THE FORECAST FOR THIS EVENING...ESPECIALLY WEST
OF US281. MOST MODELS LOOK TO BE STARTING THE CONVECTION AS
CELLULAR BEFORE MORPHING INTO A BROKEN SQUALL LINE AS IT CROSSES
SOUTH TEXAS. MOST MODELS DO HAVE EVERYTHING THROUGH THE VALLEY BY
JUST AFTER MIDNIGHT...SO HAVE FOCUSED BIGGEST THREATS DURING THE
SUNSET TO MIDNIGHT. SATURDAY WILL BE THE BRIEF STABILIZATION
BEHIND THE OVERNIGHT THUNDERSTORMS...SO DAYTIME CONVECTION WILL BE
LOWER. TEMPERATURES WILL BE SIMILAR TO TODAY...WITH HIGHS A FEW
DEGREES EITHER SIDE OF 90 AND TD VALUES AROUND 75. THIS EQUATES TO
HEAT INDEX VALUES OF 100 TO 105 IN THE AFTERNOON. THUNDERSTORM
CHANCES SATURDAY WILL HINGE ON THE ABILITY OF THE DRYLINE TO PUSH
EASTWARD INTO THE WESTERN VALLEY IN THE EVENING. THIS SCENARIO
LOOKING MORE UNLIKELY WITH STEERING FLOW STILL FROM THE SW...SO
RAIN CHANCES REMAIN LOW SATURDAY INTO SATURDAY NIGHT.

LONG TERM /SUNDAY THROUGH THURSDAY/...A FLAT PRESSURE FIELD WITH
LIGHT SOUTH WINDS AND CONTINUED MOIST LOW LEVEL AIR WILL GREET
RESIDENTS SUNDAY MORNING. THERE MAY BE A FEW LINGERING SHOWERS FROM
SATURDAY NIGHT STILL MOVING INTO OR OVER THE MID AND UPPER VALLEY. A
MID LEVEL SHORT WAVE WILL BE OVER THE FOUR CORNERS AND MOVING EAST
TOWARD NORTH TEXAS. SUNDAY HIGH TEMPS WILL HIT THE LOWER 90S ACROSS
MUCH OF THE AREA EXCEPT FOR THE IMMEDIATE COAST. A PUSH OF DRIER AIR
WILL ENTER THE UPPER VALLEY BY AFTERNOON BUT WILL MOST LIKELY NOT
MAKE IT TO THE COAST...WHICH WILL REMAIN ENSCONCED WITH HIGHER DEW
POINT AIR. A FEW SHOWERS OR THUNDERSTORMS MAY POP UP ALONG THE
BOUNDARY OVER THE HILL COUNTRY AND EXTEND SOUTH THROUGH THE COASTAL
BEND AND RIO GRANDE PLAINS...AS CYCLOGENESIS OCCURS OVER NORTH
CENTRAL TEXAS...AND ESPECIALLY AS MID LEVEL ENERGY MAY BE PRESENT...
WITH CONVECTION TOUCHING THE NORTH AND NORTHEAST PARTS OF THE CWA
LATER ON SUNDAY. LOW TEMPS WILL BE IN THE 70S ONCE MORE SUNDAY NIGHT
AS SOME CONVECTION HANGS ON TO THE NORTH.

AT THIS POINT...MONDAY THROUGH MID WEEK...THE FORECAST BECOMES A
LITTLE MORE COMPLEX...WITH DETAILS MORE DIFFICULT TO SUSS OUT. AT
FIRST LOOK...THE LONG RANGE MODELS ARE NOT TOO DIFFERENT AND A
CONSENSUS SHOULD BE ACCEPTABLE. A WEAK INITIAL FRONT WILL PUSH INTO
THE RIO GRANDE PLAINS AND EVEN THE UPPER VALLEY EARLY MON MORNING.
HIGH TEMPS WILL BE MILDER...IN THE MID 80S. SOME CONVECTION MAY
CONTINUE ACROSS THE NORTH AND THEN NORTHEAST THROUGH THE DAY AS THE
FRONT PULLS TO THE NORTHEAST. SOME CLEARING AND DRIER AIR MONDAY
NIGHT WILL LEAD TO OVERNIGHT LOWS IN THE 60S AND 70S.

THE MAIN SECONDARY FRONT WILL ARRIVE TUESDAY MORNING...BUT THE
EXTREME LOWER VALLEY MAY NOT CLEAR COMPLETELY UNTIL LATER IN THE
DAY. NORTH WINDS WILL INCREASE TO MODERATE OR BREEZY DURING THE DAY
WITH HIGHS AROUND 80. DID LEAN MORE TOWARD THE ECMWF ON WINDS FOR
THE DAY AS IT WAS A LITTLE STRONGER THAN THE GFS AND DIDN`T WANT TO
COME UP SHORT AT THIS POINT. THE H5 PATTERN WILL SLOWLY VEER AS THE
UPPER TROUGH EJECT  OVER OKLAHOMA AND UPSTREAM RIDGING BEGINS TO
PLAY A BIGGER ROLE. NIGHT TIME LOWS WILL DECREASE FURTHER TO THE
UPPER 50S AND LOWER 60S.

HIGH PRESSURE WILL SETTLE OVER NORTH TEXAS ON WEDNESDAY WITH FINE
WEATHER CONDITIONS. MILDER TEMPS AND SUNNIER SKIES WILL PREVAIL
THROUGH THURSDAY.

MARINE...
NOW THROUGH SATURDAY NIGHT...WINDS HAVE VARIED CONSIDERABLY
ACROSS THE GULF WATERS...WITH 15G20KTS ALONG TEH COAST...WHILE
BEYOND 30NM WINDS ARE ONLY AROUND 5KTS. WINDS SHOULD EVEN OUT
OVERNIGHT...AROUND 10KTS ALL LOCATIONS. SEAS WILL REMAIN RIGHT
AROUND 3 FT TONIGHT...WITH A SLIGHT INCREASE TO NEAR 4 FEET LATE
TOMORROW. NOT EXPECTING ANY AADVISORIES THROUGH THE NEXT 36
HOURS. A SQUALL LINE IS EXPECTED TO REACH THE GULF WATERS LATER
TONIGHT... WHICH WOULD BRING DOWNPOURS...VARIABLY GUSTY WINDS AND
FREQUENT LIGHTNING AS IT PASSES.

SUNDAY THROUGH TUESDAY...A WEAK PRESSURE GRADIENT OVER THE NORTHWEST
GULF WILL RESULT IN LIGHT SOUTHEAST WINDS AND LOW SEAS INITIALLY.
WINDS WILL INCREASE TO MODERATE SUNDAY AS A SURFACE TROUGH DEVELOPS
NEAR THE BIG BEND...TIGHTENING THE GRADIENT. AS THE TROUGH SHIFTS
TOWARD THE COAST SUNDAY NIGHT...WINDS WILL AGAIN DECREASE. LIGHT
WINDS WILL BECOME VARIABLE AS HIGH PRESSURE APPROACHES FROM UPSTREAM
MONDAY AND MONDAY NIGHT. NORTH WINDS WILL INCREASE AFTER A FRONTAL
PASSAGE TUESDAY MORNING...BECOMING MODERATE AND THEN STRONG BY TUE
AFTERNOON...WHEN SMALL CRAFT ADVISORY CONDITIONS WILL DEVELOP. A FEW
SHOWERS WILL BE POSSIBLE TUE DURING THE DAY. WAVE HEIGHTS WILL THEN
BUILD TOWARD SEVEN FT TUESDAY NIGHT. CONDITIONS WILL SLOWLY IMPROVE
ON WEDNESDAY AS HIGH PRESSURE BEHIND THE FRONT SPREADS OVER THE
AREA.

&&

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

$$

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

66/67


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