Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 261748
AFDBRO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
1248 PM CDT THU MAR 26 2015

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

&&

.AVIATION...FRONT WILL MOVE ACROSS THE AREA IN THE NEXT TWO
HOURS INCREASING NORTHERLY WINDS WITH GUSTS AND THE POTENTIAL
FOR ISOLATED THUNDERSTORMS TO DEVELOP. SOME OF THESE STORMS COULD
BE STRONG PRODUCING GUSTS UP TO 45 TO 50 KNOTS WITH FREQUENT
LIGHTNING ACTIVITY. BY THE EVENING HOURS NORTH WINDS WILL GUSTS
OVERNIGHT BUT BEGIN TO LOWER EARLY IN THE MORNING. CONDITIONS
IMPROVE FRIDAY WITH DRY AIR MOVING INTO THE AREA.

&&

.PREV DISCUSSION... /ISSUED 1201 PM CDT THU MAR 26 2015/

DISCUSSION...THE FRONT HAS A SLOWER PROGRESSION SOUTH TODAY
WITH A FEW ISOLATED THUNDERSTORMS BEGIN TO DEVELOP ALONG THE
EDGE OF THE FRONT. AT THIS TIME...CHANGES WERE MADE TO THE
FRONTAL ARRIVAL AND LOWER TEMPERATURES. THE REMAINDER OF THE
FORECAST REMAINS THE SAME.

PREV DISCUSSION... /ISSUED 628 AM CDT THU MAR 26 2015/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...FOG AND LOW CIG ARE LEADING TO PREVAILING LIFR/IFR
CONDITIONS THIS HOUR AND THAT WILL LIKELY CONTINUE FOR AT LEAST
ANOTHER TWO HOURS BEFORE SUNSHINE BEGINS TO GET SOME MIXING GOING.
AN IMPROVEMENT TO MVFR IS THEN EXPECTED FOR A FEW HOURS BEFORE A
FRONT SWEEPS INTO THE AREA. THE FRONT WILL LIKELY SPARK SHOWERS
AND A FEW THUNDERSTORMS. HAIL/WIND AND PRODIGIOUS LIGHTNING WILL
BE THREATS WITH AND INVOF CONVECTION ALTHOUGH THE SPEED OF THE
FRONT MAY LIMIT TOTAL TSTORM COVERAGE. TEMPO GROUPS MARK THE MOST
LIKELY WINDOW OF ACTIVITY. DEEPER DRY AIR MOVES IN A FEW HOURS
BEHIND THE FRONT LEADING TO AN IMPROVEMENT IN FLIGHT CONDITIONS
WITH VFR LIKELY BY SUNSET TONIGHT PERSISTING THROUGH THE
OVERNIGHT. /68-JGG/

PREV DISCUSSION... /ISSUED 410 AM CDT THU MAR 26 2015/

SHORT TERM /NOW THROUGH FRIDAY/...

RELEVANT FEATURES...RICH BOUNDARY LAYER MOISTURE IS SPREAD ACROSS
DEEP SOUTH TEXAS THIS MORNING WITH DEWPOINTS IN THE LOWER 70S. A
BROAD UPPER LEVEL TROUGH IS AMPLIFYING OVER NORTHWESTERN MEXICO
AND WEST SOUTHWESTERLY FLOW ROUNDING THE BASE OF THIS TROUGH HAS A
COUPLE OF VERY SHORT WAVE RIPPLES EMBEDDED WITHIN IT WHICH ARE
ASSOCIATED WITH SOME MODEST CONVECTION. THERE IS A SHARP TERRAIN
INDUCED CAP PRESENT AT 750MB LOCALLY...BUT ABOVE THAT LAYER
IMPRESSIVELY STEEP LAPSE RATES EXIST...WHICH RENDERS AROUND 2600
J/KG OF MUCAPE ON THE PREVIOUS EVENINGS OBSERVED SOUNDINGS WHICH
HAS LIKELY HELD OR IMPROVED SLIGHTLY THROUGH THE NIGHT. A SHARP
COLD FRONT...BEING PUSHED BY INCREASED UPPER CONVERGENCE BEHIND
THE AMPLIFYING TROUGH IS SLICING THROUGH NORTH CENTRAL TEXAS
TONIGHT APPEARING TO BE ABOUT 50 MILES NORTH OF SAN ANTONIO AT 3
AM.

TODAY...
IMPACTS...CONDITIONAL RISK FOR SEVERE THUNDERSTORMS WITH 50 TO 60
MPH WINDS AND HAIL TO THE SIZE OF QUARTERS ALONG AND SOUTH OF A
LINE FROM MCALLEN TO PORT MANSFIELD AND MOST OF THE LOWER TEXAS
COASTAL WATERS.

THE SURFACE FRONT IS EXPECTED TO ARRIVE BY ABOUT 9 TO 11 AM
SWEEPING THROUGH THE AREA IN RELATIVELY QUICK ORDER. AT THE TIME
OF THE FRONTS ARRIVAL THERE WILL BE A RELATIVELY FAVORABLE
ENVIRONMENT FOR STRONG TO SEVERE THUNDERSTORMS WITH ABOUT 2800
J/KG OF MIXED LAYER CAPE FOR PREFRONTAL BOUNDARY LAYER PARCELS AND
AROUND 3000 J/KG OF MOST UNSTABLE CAPE ABOVE THE FRONTAL SLOPE AS
IT SLICES THROUGH THE AREA. 0-6KM BULK SHEAR VALUES AROUND 35 TO
45 KNOTS SHOULD BE SUFFICIENT TO AID IN STORM ORGANIZATION AND
ENHANCED HAIL POTENTIAL. FREEZING LEVELS ARE FAIRLY HIGH...AT
AROUND 11500 FT BUT LARGE CAPE AND SHEAR IN THE HAIL GROWTH REGION
SUGGESTS THAT IF UPDRAFTS CAN GET GOING LARGE HAIL WOULD BE
POSSIBLE. ONE OF THE AFOREMENTIONED RIPPLES LOOKS TO ARRIVE ABOUT
THAT TIME AS WELL PUTTING THE REGION IN A DIFFLUENT/DIVERGENT FLOW
ALOFT AIDING IN GOOD MID LEVEL ASCENT...FURTHER STEEPENING LAPSE
RATES AND HELPING TO LIFT OUT THE EXISTING CAPPING INVERSION.
PRIMARY CONCERN WITH SVR POTENTIAL THOUGH IS TOTAL CONVECTIVE
COVERAGE AND THE SLOPE/SPEED OF THE FRONTAL PASSAGE. THE NAM12
BEGINS TO SHOW SOME FAIRLY SIGNIFICANT FRONTOLYSIS AS IT
APPROACHES WHICH MARKEDLY REDUCES LOW LAYER CONVERGENCE. HOWEVER
THAT MODEL AND OTHERS ALSO SHOW GOOD 850MB SUPPORT BEHIND THE
FRONT. THE FRONT CURRENTLY LOOKS PRETTY STOUT AND TEND TO SUPPORT
THE GLOBAL MODELS AND SREF ASSERTION THAT THERE WILL BE SUFFICIENT
LOW LAYER CONVERGENCE FOR PRETTY HEALTHY CONVECTIVE COVERAGE. SO
WITH THAT...NUDGED POPS UP A BIT AND ADDED A MENTION OF SVR WITH
HAIL/WIND THE MAIN THREAT ALONG A LINE FROM MCALLEN TO PORT
MANSFIELD...AND THEN INCLUDED ALL OF THE COASTAL WATERS WHERE LOW
LEVEL INSTABILITY SHOULD HOLD ON LONGER THROUGH THE DAY. FAST
FRONTAL MOVEMENT MAY UNDERCUT THE BEST UPDRAFTS BEFORE THEY GET
FULLY DEVELOPED SO THE RISK REMAINS CONDITIONAL.

TONIGHT...COOLER AND DRIER WEATHER EXPECTED TONIGHT WITH
TEMPERATURES MADE A LITTLE MORE MILD WITH PERSISTENT NORTH WINDS.
A SLIGHT CHANCE OF SHOWERS PERSISTS EARLY THIS EVENING OVER THE
GULF BEFORE CLEARING OUT COMPLETELY ALTHOUGH RELATIVELY STRONG
NORTH WINDS WILL LIKELY PERSIST MOST OF THE NIGHT.

FRIDAY...WIND SPEEDS DROP OFF AS THE WIND SHIFTS TO THE EAST. SUNNY
SKIES SHOULD ALLOW TEMPERATURES TO WARM INTO THE UPPER 70S AREA WIDE
WITH PLEASANT HUMIDITY LEVELS. /68-JGG/

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...AN AMPLIFIED AND
SLOWLY PROGRESSIVE H5 PATTERN WILL BE IN PLAY FRIDAY NIGHT. RIDGING
OVER THE ENTIRE WEST WITH TROUGHING OVER THE ENTIRE EAST WILL BE THE
NAME OF THE GAME. SURFACE HIGH PRESSURE OVER DEEP SOUTH TEXAS AND
DRY AIR UNDER NORTHWEST MID LEVEL FLOW WILL PROVIDE CHAMBER OF
COMMERCE WEATHER SATURDAY...WITH MOSTLY SUNNY SKIES...LIGHT WINDS
AND HIGH TEMPERATURES IN THE LOWER 80S EXCEPT UPPER 70S NEAR THE
COAST. THOSE TEMPS WILL BE JUST A HAIR ABOVE NORMAL. A CLEAR NIGHT
SATURDAY WITH LOWS FROM THE MID 50S TO MID 60S WILL LEAD TO ANOTHER
NICE DAY SUNDAY...SIMILAR TO SATURDAY BUT MAYBE A DEGREE OR TWO
WARMER. MONDAY WILL SEE A FEW MORE CLOUDS AND ANOTHER COUPLE OF
DEGREES ADDED ONTO THE MERCURY...PUSHING VALUES ABOVE NORMAL.

STARTING SATURDAY...A MID LEVEL WEAKNESS WILL MOVE EAST FROM THE
EASTERN PACIFIC TOWARD SOUTHERN CALIFORNIA...ESSENTIALLY UNDER
CUTTING THE MEAN RIDGE...FROM WHENCE IT WILL CONTINUE EAST AND
ASHORE THROUGH THE WEEKEND. BY MONDAY IT WILL RESIDE OVER THE
GADSDEN PURCHASE...DESTABILIZING DOWNSTREAM CONDITIONS TO WHERE...
WHEN COMBINED WITH A MODERATE SOUTHEAST WIND...WE COULD SEE SOME
COASTAL SHOWER ACTIVITY...AKIN TO A SEA BREEZE...DEVELOP. THE MID
LEVEL FEATURE WILL FURTHER OPEN UP MONDAY NIGHT INTO TUESDAY AS IT
MOVES ACROSS NORTH AND CENTRAL TEXAS...AND SOME SHOWER AND EVEN
TSTM ACTIVITY WILL BE POSSIBLE OVER DEEP SOUTH TEXAS FROM LATE
MONDAY THROUGH TUESDAY NIGHT. THE ECMWF MODEL GUIDANCE IS MORE
ROBUST WITH THE RAIN SCENARIO THAN THE GFS MODEL...WHICH IS QUITE
MODEST. BY LATE TUESDAY THE TROUGH WILL BE DOWNSTREAM AND DRY AIR
WILL BE BACK IN THE PICTURE...WITH A MID LEVEL FLOW OUT OF THE
WEST NORTHWEST KEEPING THINGS ON THE STABLE AND DRY SIDE. BY
WEDNESDAY A MORE ZONAL PATTERN WILL HAVE EVOLVED OVER THE SOUTHERN
PART OF THE COUNTRY WITH A MORE WAVY PATTERN RESEMBLING CLASSICAL
POLAR FRONT THEORY ACROSS THE NORTHERN TIER STATES.

TO SUMMARIZE...FAIR WEATHER EXCEPT FOR A BRIEF PERIOD OF UNSETTLED
CONDITIONS NEXT MONDAY NIGHT THROUGH TUESDAY.

MARINE...
NOW THROUGH FRIDAY...SCATTERED TO NUMEROUS SHOWERS AND
THUNDERSTORMS ARE EXPECTED TO DEVELOP ALONG AND BEHIND A COLD
FRONT AS IT SWEEPS ACROSS THE COAST...SOME OF THESE STORMS MAY
PRODUCE LARGE HAIL AND STRONG WINDS. A SMALL CRAFT ADVISORY HAS
ALSO BEEN ISSUED FOR STRONG NORTH WINDS AND ROUGHENING SEAS BEHIND
THE FRONT FOR ALL WATERS THROUGH LATE THIS EVENING. IMPROVED
CONDITIONS AND MODERATING SEAS ARE FORECAST FOR FRIDAY AMID LIGHT
NORTHEAST WINDS.

FRIDAY NIGHT THROUGH MONDAY...HIGH PRESSURE WILL BE CENTERED OVER
THE NORTHWEST GULF FRIDAY NIGHT...WITH LOW SEAS AND LIGHT WINDS
ACROSS THE LOWER TEXAS COAST AND MARINE AREAS. MODERATE SOUTHEAST
TO SOUTH WINDS WILL DEVELOP SATURDAY AND SATURDAY NIGHT AS THE
HIGH PRESSURE AREA WEAKENS AND LOWER PRESSURE DEVELOPS UPSTREAM
OVER THE TEXAS PANHANDLE. THE MODERATE SOUTH SOUTHEAST WINDS WILL
CONTINUE THROUGH MONDAY AND WILL ALSO SUPPORT MODERATE SEAS.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...HIGH RIP CURRENT RISK THROUGH LATE TONIGHT FOR TXZ251-256-257.

GM...SMALL CRAFT ADVISORY UNTIL 1 AM CDT FRIDAY FOR GMZ130-132-135-
     150-155-170-175.

&&

$$

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