Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 230718 AAC
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
118 AM CST SUN NOV 23 2014

.DISCUSSION...SQUALL LINE QUICKLY MOVING OFFSHORE AND SKIES ARE
CLEARING WITH A VERY LIGHT SOUTHWEST FLOW DEVELOPING. COOLER
TEMPERATURES AND THE WET SOIL FROM THE RAIN THAT MOVED THROUGH THE
REGION IS RESULTING FOG FORMATION OVER UPPER AND MIDDLE RIO GRANDE VALLEY.
AS THE UPPER TROUGH CONTINUES TO MOVE EAST SKIES WILL CONTINUE TO
CLEAR WITH THE FOG TO SPREAD EAST TOWARDS THE COAST. WILL HOLD OFF
ON ISSUANCE OF DENSE FOG ADVISORY WITH JUST ENOUGH WEST TO
SOUTHWEST WIND TO KEEP FOG FROM SOCKING US IN. HOWEVER DENSE
PATCHY FOG WILL BE MENTIONED IN THE OVERNIGHT AND EARLY MORNING
FORECAST WITH NOWCAST COVERING THE FOG OVERNIGHT. WILL CONTINUE
TO MONITOR FOR THE CHANCE OF WIDESPREAD DENSE FOG.

&&

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

&&

.AVIATION...THUNDERSTORMS HAVE MOVED WELL EAST INTO THE GULF AND
SKIES ARE CLEARING. HOWEVER FOG IS FORMING AND WILL IMPACT THE
TAFS SITES THROUGH AT LEAST MID MORNING SUNDAY. VISIBILITY TO
LOWER TO LIFR AND POSSIBLY VLIFR FOR A FEW HOURS. ONCE THE FOG
DISSIPATES BY OR BEFORE 15Z VFR WITH CLEAR SKIES TO PREVAIL.


&&

.PREV DISCUSSION... /ISSUED 1116 PM CST SAT NOV 22 2014/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...LINE OF THUNDERSTORMS IS CURRENTLY MOVING ACROSS MFE
AT THIS TIME AND MOVE EAST IN THE NEXT 30 MINUTES. THIS ACTIVITY
IS PRODUCING HEAVY DOWNPOURS...GUSTY WINDS...AND FREQUENT LIGHTNING.
IT SHOULD PASS THROUGH HRL AND BRO AROUND 05 TO 07Z. THE CONVECTION
WILL MOVE EAST INTO THE COASTAL WATERS AS WESTERLY FLOW COMES IN
BEHIND THIS TROUGH. MVFR CIGS WILL PREVAIL OVERNIGHT AND BEGIN TO
IMPROVE CLOSER TO SUNRISE. SUNDAY THE SOUTHWESTERLY WINDS WILL
PREVAIL BUT WILL REMAIN LIGHT THROUGH THE DAY THEN SOUTHEAST FLOW
RETURNS BY THE EVENING.

PREV DISCUSSION... /ISSUED 922 PM CST SAT NOV 22 2014/

DISCUSSION...STILL MONITORING CONVECTION OVER THE AREA. THE
STRONGEST ACTIVITY...IN THE FORM OF A SEVERE SQUALL...IS
OVER THE GULF WATERS. ADDITIONAL CELL CLUSTERS ARE DEVELOPING
OVER HIDALGO COUNTY AND FURTHER SOUTHWEST INTO TAMAULIPAS AND
NUEVO LEON. RAIN APPEARS TO HAVE COOLED THE SURFACE SUFFICIENTLY
IN HIDALGO COUNTY AND POINTS FURTHER WEST TO ELIMINATE ANY
REMAINING SURFACE BASED INSTABILITY. THIS WILL RESULT IN A
REDUCTION IN THE WIND DAMAGE THREAT WITH ANY ADDITIONAL CELLS THAT
GET GOING. MUCAPES AROUND 500 TO 800 J/KG APPEAR TO ALSO ELIMINATE
ANY HAIL THREAT AS WELL WHICH GIVES US CONFIDENCE THE SEVERE
THUNDERSTORM WATCH CAN EXPIRE AT 10 PM.

THE ONLY EXCEPTION FOR NOW IS CAMERON COUNTY WHERE SURFACE
DEWPOINTS REMAIN IN THE LOW 70S. IT APPEARS THE SURFACE HAS STILL
COOLED SUFFICIENTLY ENOUGH TO ELIMINATE SURFACE BASED INSTABILITY
BUT THE ADDITIONAL UPSTREAM CONVECTION TO THE WEST AT LEAST BEARS
MONITORING AS FAVORABLE DEEP AND LOW LAYER SHEAR PROFILES PERSIST
OVER THE AREA AND ARE EXPECTED TO FOR ANOTHER FEW HOURS. AT LEAST
SOME ADDITIONAL MID LEVEL ASCENT MAY HELP KEEP THIS REGION AT
LEAST MARGINALLY UNSTABLE THROUGH THE MIDNIGHT HOUR BUT THE THREAT
IS LIKELY TOO MARGINAL TO NECESSITATE A CONTINUATION OF THE SEVERE
THUNDERSTORM WATCH BEYOND 10 PM. /68-JGG/

PREV DISCUSSION... /ISSUED 535 PM CST SAT NOV 22 2014/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...STRONG THUNDERSTORMS ARE BEGINNING TO DEVELOP OVER
WESTERN ZAPATA COUNTY AT THIS TIME AND CONTINUE MOVING NE AT
AROUND 45 TO 50 MPH. THE STRONG CONVECTION IS EXPECTED TO REACH
THE TERMINALS AFTER 02Z AND PRODUCE STRONG GUST WINDS...DANGEROUS
LIGHTNING...MODERATE TO HEAVY DOWNPOURS WHICH WILL LOWER VISIBILITY
QUICKLY. THIS ACTIVITY WILL MOVE EAST AND INTO THE COAST AFTER 05Z.
AS THE TROUGH AXIS MOVES FURTHER EAST AND EXIST THE AREA...GOOD
VFR CONDITIONS WILL PREVAIL IN THE EARLY MORNING HOURS WITH A
SOUTHWEST FLOW THROUGH THE DAY.

PREV DISCUSSION... /ISSUED 317 PM CST SAT NOV 22 2014/

DISCUSSION...UPDATED ALL THE PRODUCTS FOR SEVERE THUNDERSTORM
WATCH 557. /68-JGG/

PREV DISCUSSION... /ISSUED 226 PM CST SAT NOV 22 2014/

SHORT TERM /NOW THROUGH SUNDAY NIGHT/...

IMPACTS...POTENTIAL FOR SEVERE THUNDERSTORMS CAPABLE OF DAMAGING
WINDS AND LARGE HAIL...WITH AN ISOLATED TORNADO POSSIBLE.

RELEVANT FEATURES...
UPPER LEVEL LOW CENTER IS OVER CHIHUAHUA STATE MEXICO...ABOUT ON
SCHEDULE WITH ITS PROGRESS SLOWED BY A BROAD SOUTHWESTERLY 70 TO
90 KT JET MAXIMUM OVER SOUTH TEXAS AND NORTHEASTERN MEXICO. A
STRONGER SOUTHEASTERLY JET IS MARCHING ACROSS THE DESERT SOUTHWEST
WITH WIND SPEEDS AROUND 110 TO 120 KTS. THIS WILL REACH THE UPPER
CLOSED LOW OVER THE NEXT FEW HOURS AND TILT THE TROUGH NEGATIVELY
AND RESULT IN A LARGE AMOUNT OF DIFFLUENCE/DIVERGENCE OVER SOUTH
TEXAS AND NORTHERN MEXICO. LEE TROUGHING AND RESPONSE TO THIS
UPPER LEVEL FEATURE IS ALREADY UNDERWAY WITH STRONG SOUTHEAST
WINDS OCCURRING ACROSS MOST OF THE REGION WITH GUSTS PUSHING 30 TO
35 MPH UNDER A THIN LAYER OF OVERCAST GENERATED BY WEAK WARM AIR
ADVECTION. 1800 UTC SPECIAL RELEASE SHOWS A MODEST CAP AROUND
800MB TO SURFACE BASED PARCELS BUT RELATIVELY STRONG MID LEVEL
LAPSE RATES AND STRONG LOW LAYER AND DEEP LAYER WIND SHEAR. THE
1200 UTC SOUNDING FROM MONTERREY MEXICO SHOWED A MUCH SHARPER
TERRAIN INDUCED INVERSION AND THE TRAJECTORY OF WINDS OVER
NORTHEASTERN TAMAULIPAS AND THE ABSENCE OF ANY CONVECTION
CURRENTLY SUGGESTS AT LEAST SOME OF THIS ELEVATED MIXED LAYER IS
SPREADING OVER SOUTH TEXAS...WHICH IS COMMON IN SUCH REGIMES.

LATE THIS AFTERNOON/TONIGHT...
THE PRESENCE OF THE AFOREMENTIONED CAP WILL LIKELY KEEP CONVECTION
AT BAY IN THE LATE AFTERNOON WHICH WILL PREVENT STORMS FROM
TAPPING THE FAVORABLE SHEAR PROFILES CURRENTLY PRESENT. HOWEVER
THE ARRIVAL OF THE UPPER LEVEL LOW WILL RESULT IN VERY STRONG
LARGE SCALE ASCENT WHICH SHOULD EASILY OVERCOME ANY RESIDUAL
CAPPING. THE ARRIVAL OF THIS EXTRA UPPER LEVEL IMPULSE ALSO
STRENGTHENS 925/850MB WINDS ALONG THE COAST IN NAM/RAP GUIDANCE.

THERE IS GOOD GUIDANCE CONSENSUS ON CONVECTION INITIATING IN A FEW
HOURS OVER THE SIERRA MADRE MOUNTAINS. THIS CONCEPT IS SUPPORTED
BY VISIBLE SATELLITE SHOWING CUMULUS BEGINNING TO BUBBLE IN THE
MOUNTAINS AND PLATEAU AHEAD OF THE UPPER TROUGH. THESE TSTMS ARE
THEN EXPECTED TO MOVE NORTHEAST INTO DEEP SOUTH TEXAS BY AROUND 6
TO 7 PM TONIGHT. SHEAR PROFILES ARE EXPECTED TO BE SUPPORTIVE OF
SUPER CELLS WHICH WILL EVENTUALLY LIKELY UPSCALE INTO A SQUALL
LINE/MCS BEFORE PUSHING INTO THE GULF OF MEXICO.

STORMS THAT DEVELOP EARLY IN THE EVENING WILL HAVE BETTER SURFACE
HEATING TO WORK WITH AND LARGER MIXED LAYER CAPE VALUES. THE NWS
STORM PREDICTION CENTER HAS HIGHLIGHTED OUR WESTERN COUNTIES WITH AN
ENHANCED POTENTIAL FOR VERY LARGE HAIL...GREATER THAN TWO INCHES IN
DIAMETER...WHICH SEEMS REASONABLE GIVEN THE LARGER CAPES THAT WILL
BE AVAILABLE AT THAT TIME FRAME AMID FAVORABLE SHEAR PROFILES.

THE LARGE SCALE LIFT IN THE MID AND UPPER LEVELS IS EXPECTED TO
BE SUFFICIENT HOWEVER TO KEEP AROUND 1000 TO 1500 J/KG OF MLCAPE
AVAILABLE AS THE STORMS/CLUSTERS MOVE EAST AMID STRONG DEEP LAYER
SHEAR. 0-3 KM CAPE VALUES WILL BE AROUND 500 TO 800 J/KG WITH LOW
LCL HEIGHTS. ADDITIONALLY INCREASES IN THE 850/925MB WIND FIELDS
AS THE UPPER LOW STRENGTHENS LOW PRESSURE TO OUR NORTHWEST RESULTS
IN 0-1KM SHEAR VALUES OF 20 TO 25 KTS CREATING ABOUT 150 M2/S2 OF
STORM RELATIVE HELICITY EAST OF THE 281 CORRIDOR THIS EVENING.
THIS WOULD SUPPORT A POTENTIAL FOR TORNADOES IN EITHER DISCRETE
SUPER CELLS OR QUASI LINEAR CONVECTIVE STRUCTURES AS THE SYSTEM
MOVES EASTWARD IN ADDITION TO A MORE WIDESPREAD THREAT OF DAMAGING
WINDS. STORM MOTION WILL ALSO LIKELY BE QUICK...AT 40 MPH OR
MORE...ESPECIALLY IN LINEAR STRUCTURES. STORM MOTION SHOULD BE TOO
FAST FOR SIGNIFICANT FLOODING CONCERNS ALTHOUGH DEEP MOISTURE WILL
SUPPORT BRIEF HEAVY RAINFALL AND POSSIBLY SOME LOCALIZED FLOODING.

A SURGE OF DEEP DRIER AIR MOVING IN FROM 850-700MB MOVES IN BEHIND
THE FRONT TONIGHT...ENDING RAINFALL/STORM CHANCES.

SUNDAY...MODERATE WESTERLY WINDS KEEP PUSHING IN DRIER AIR THROUGH
THE DAY SUNDAY LEADING TO A MUCH MORE TRANQUIL AND DRY WEATHER
PATTERN. TEMPERATURES WILL STILL BE FAIRLY WARM...INTO THE LOW 80S
BUT HUMIDITY VALUES WILL BE SIGNIFICANTLY LOWER.

SUNDAY NIGHT...A PUSH OF HIGH PRESSURE FROM THE NORTH WILL ARRIVE
LATE SUNDAY NIGHT BUT LIKELY NOT QUICKLY ENOUGH TO SIGNIFICANTLY
ALTER OVERNIGHT TEMPS. LOWS WILL BE IN THE MID TO UPPER 50S. /68-JGG/

LONG TERM /MONDAY THROUGH SATURDAY/...A MILD WEATHER WEEK WILL
PREVAIL DURING THE LONG TERM.

A WARM TO HOT SUNDAY WITH HIGH TEMPERATURES IN THE MID 80S WILL
TRANSITION INTO MORE SEASONAL WEATHER MONDAY THROUGH THE WEEK AS
MODIFIED MARITIME POLAR AIR FROM THE EAST PACIFIC ARRIVES FROM THE
WEST. THE PACIFIC AIR WILL ARRIVE IN TWO PULSES...ONE MONDAY AND
ANOTHER TUESDAY...USHERED ACROSS BY MID LEVEL SHORT WAVE TROUGHS
DIGGING SOUTHEAST DOWN THE SIDE OF A LARGE SCALE RIDGE WEST OF THE
ROCKIES. THE TWO PULSES WILL BE ACCOMPANIED BY DRY SURFACE AIR...
THOUGH A FEW CLOUDS MAY MATERIALIZE NEAR THE COAST MON AND TUE
DURING THE DAY BEFORE DRIER AIR SIMPLY OVERWHELMS THE AREA. HIGH
TEMPS WILL BE IN THE 70S EACH DAY...WITH LOWS IN THE 40S MONDAY
AND TUESDAY NIGHT AND THE 50S WED AND THU NIGHT. NORTH WINDS
THROUGH TUESDAY WILL BECOME LIGHT ON WED AND THEN TRANSITION TO
LIGHT SOUTHEAST BY THURSDAY...WHICH WILL SIGNAL THAT SFC HIGH
PRESSURE IS SHIFTING EAST OF THE AREA WHILE THE UPSTREAM RIDGE
BREAKS DOWN...AND THE BEGINNING OF MOISTURE RETURN AND SLIGHTLY
WARMER TEMPERATURES TOWARD THE END OF THE WEEK. OVERALL THROUGH...
A MILD AUTUMN WEEK IS AHEAD WITH LOTS OF SUN...AND NEAR NORMAL
TEMPS EXCEPT FOR A LITTLE COLDER THAN NORMAL TUE AND WED NIGHT.

MARINE...
TODAY THROUGH SUNDAY NIGHT....SMALL CRAFT ADVISORY REMAINS IN
EFFECT FOR ALL OF THE LOWER TEXAS COAST TODAY...AND FOR THE GULF
OF MEXICO WATERS TONIGHT DUE TO STRONG WINDS AND ROUGH SEAS.
IMPROVING CONDITIONS ARE FORECAST THROUGH SUNDAY WITH MORE
MODERATE SEAS AND LIGHT TO MODERATE WESTERLY WINDS. FAVORABLE
CONDITIONS ARE FORECAST SUNDAY NIGHT BEFORE ANOTHER SURGE OF HIGH
PRESSURE INCREASES NORTHERLY WINDS EARLY MONDAY MORNING.

MONDAY THROUGH THURSDAY...MODERATE NORTH WINDS MONDAY WILL REACH
CAUTION LEVELS ON THE GULF BY AFTERNOON...15 TO 20 KNOTS WITH
SEAS BUILDING TOWARD 6 FEET IN THE WAKE OF A PACIFIC COOL FRONT.
REINFORCING HIGH PRESSURE TUESDAY WILL RESULT IN STRONGER GUSTY
NORTH WINDS TUESDAY AFTERNOON THROUGH EARLY EVENING...POSSIBLY
REACHING 20 KNOTS AND LOW END SMALL CRAFT ADVISORY CONDITIONS WITH
SEAS BUILDING TOWARD 7 FEET IN A FEW SPOTS.

WIND CONDITIONS WILL IMPROVE TUESDAY NIGHT AND WEDNESDAY THOUGH
SEAS WILL REMAIN MODERATE. A LIGHT TO MODERATE SOUTHEAST WIND WILL
SET UP ON THURSDAY.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  59  73  55  70 /   0   0   0  10
BROWNSVILLE          59  74  54  71 /   0   0   0  10
HARLINGEN            58  73  51  70 /   0   0   0  10
MCALLEN              58  74  51  70 /   0   0   0   0
RIO GRANDE CITY      57  73  48  70 /   0   0   0   0
SOUTH PADRE ISLAND   64  73  61  70 /   0   0   0  10

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT ADVISORY UNTIL 6 AM CST EARLY THIS MORNING FOR
     GMZ150-155-170-175.

&&

$$

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

59...AVIATION/SHORT TERM




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