Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 141730 AAC
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
1230 PM CDT SUN SEP 14 2014

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

&&

.AVIATION...CHALLENGING AVIATION FORECAST NEXT 6 HOURS.
OVERRUNNING NEAR A VERY LOW FRONTAL INVERSION AT 500 TO 1000 FT
HAS KEPT THE MIDDLE VALLEY SOCKED IN LIFR/IFR CONDITIONS. A
PUSH OF NORTHEASTERLY WINDS IS MOVING IN AND SHOULD START TO MIX
AND BREAK THAT CLOUD LAYER UP AND SHOWERS AND STORMS SHOULD BEGIN
TO DEVELOP ON THE DIFFERENTIAL HEATING BOUNDARY SET UP NEAR THE
COAST FROM THE GRADIENT OF CLOUDY AND SUNNY AREAS THIS MORNING.
THOSE SHOWERS AND STORMS WILL MOVE WESTWARD THROUGH THE AFTERNOON
BUT MAY NOT MAKE IT AS FAR INLAND AS HIGHWAY 281. CONFIDENCE ON
MFE IMPROVING TO MVFR/VFR IS LOW BUT THAT DOES STILL APPEAR TO BE
THE MOST LIKELY OUTCOME. FURTHER EAST WARMING TEMPERATURES AT
HRL/BRO MAKE IMPROVEMENT THERE APPEAR A LITTLE MORE LIKELY.

TONIGHT ABUNDANT LOW LEVEL MOISTURE WILL LIKELY AID IN REFORMING
CLOUD COVER IN THE LOW MVFR/HIGH IFR CATEGORY BUT THE FRONTAL
INVERSION WILL LIKELY BE SHIFTED BY THESE INCOMING NORTHEASTERLY
WINDS AND THE EXACT PLACEMENT IS CHALLENGING. ANOTHER TROPICAL
WAVE ARRIVES MONDAY WITH A FAIR COVERAGE OF SHOWERS AND
STORMS...PREVAILING WX COULD BE SHRA BY 16 TO 18Z WITH EMBEDDED
TS. NORTHWESTERLY WINDS INLAND SHOULD GIVE WAY TO NORTHEASTERLY
WINDS EVERYWHERE IN A FEW HOURS. /68-JGG/

&&

.PREV DISCUSSION... /ISSUED 851 AM CDT SUN SEP 14 2014/

DISCUSSION...WITH THE CORE OF YESTERDAYS TROPICAL WAVE INLAND MID
LEVEL WINDS HAVE SHIFTED MORE SOUTHEASTERLY IN RESPONSE TO WEAK
RIDGING OVER THE NORTH CENTRAL GULF OF MEXICO. MOISTURE CONTENT IS
STILL QUITE HIGH...BUT A LITTLE LESS THAN YESTERDAY. NAM/GFS BOTH
SHOW AN INCREASE IN 850/700MB RELATIVE HUMIDITY THIS AFTERNOON AS
WINDS IN THAT LAYER SHIFT TO THE NORTHEAST. THIS IS SUPPORTED BY
CURRENT CONVECTIVE ACTIVITY THERE AND GOES DERIVED SOUNDINGS IN
THE AREA.

WILL BE SIGNIFICANTLY LESS AVAILABLE CONVERGENCE AND FOCUSING BUT
THE ONGOING SCATTERED SHOWERS SHOULD HAVE MOIRE MOISTURE TO WORK
WITH IN THE AFTERNOON HEATING...WITH VISIBLE SATELLITE SHOWING
BREAKS STARTING TO FORM UP IN THE CLOUD COVER...AND SCATTERED TO
LOCALLY NUMEROUS SHOWERS AND STORMS SHOULD GET GOING AGAIN WITH A
SLOWER STORM MOTION THAN YESTERDAY AND PRECIPITABLE WATER VALUES
AROUND 2.2 INCHES. WIDESPREAD HEAVY RAIN AND FLOODING IS NOT
FORECAST TODAY BUT GIVEN THE SATURATED GROUND CONDITIONS LOCALIZED
URBAN/SMALL STREAM FLOODING AND IN AN OUTLIER CASE FLASH FLOODING
STILL LOOKS POSSIBLE AS MENTIONED EARLIER THIS MORNING.

FORECAST LOOKS GOOD ONLY TWEAKED PM POPS A BIT TO INCREASE AROUND
RAYMONDVILLE AND PORT MANSFIELD. /68-JGG/

PREV DISCUSSION... /ISSUED 646 AM CDT SUN SEP 14 2014/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...LATEST SATELLITE LOOP INDICATES LIFR CIGS WORKING
NORTHWARD ACROSS THE RIO GRANDE RIVER. THE LOWER CEILING WILL BE
SLOW IN LIFTING WITH ABUNDANT MOISTURE RIDING OVER A STATIONARY
BOUNDARY ALONG THE RIO GRANDE RIVER. THE LIFR CONDITIONS ARE
ENTRENCHED AT KMFE AND ARE APPROACHING KHRL AND KBRO. CONFIDENCE
IS LOW TO MEDIUM IF THE LOWER CIGS WORK THEIR WAY FAR ENOUGH
NORTHEAST TO IMPOSE IMPACTS THROUGH THE MORNING. MIXING INCREASES
BY NOON ALLOW FOR CIGS TO RISE BUT INCREASING INSTABILITY WILL
ALLOW FOR SCATTERED SHOWERS AND THUNDERSTORMS TO INCREASE IN AREAL
COVERAGE.

PREV DISCUSSION... /ISSUED 356 AM CDT SUN SEP 14 2014/

SHORT TERM /NOW THROUGH MONDAY/...UNSETTLED WEATHER TO CONTINUE
THROUGH THE SHORT TERM WITH A STATIONARY BOUNDARY JUST SOUTH OF
THE RIO GRANDE RIVER AND ANOTHER TROPICAL WAVE AND TROPICAL UPPER
LOW TO APPROACH THE LOWER TEXAS COAST MONDAY.

TODAY...WEAK OVERRUNNING CONDITIONS EXPECTED WITH A STATIONARY FRONT
EXTENDING ALONG AND JUST SOUTH OF THE RIO GRANDE RIVER. EAST TO
SOUTHEAST WINDS AT 925-700MB KEEPING A TAP OF GULF MOISTURE RIDING
OVER A SLIGHTLY COOLER N-NE WIND. CURRENT RADAR SHOWS SCATTERED
SHOWERS AND ISOLATED THUNDER DEVELOPING AND MOVING WSW OVER THE
COASTAL WATERS AND APPROACHING CAMERON AND WILLACY COUNTIES. FARTHER
SOUTH DEEPER SOUTHEAST FLOW CONTINUE TO FEED CONVECTION WHERE
YESTERDAYS TROPICAL LOW MOVED IN. MODELS SUGGEST THAT THE MEAN RH
VALUES TO REMAIN IN THE 80 PERCENT RANGE TO 700MB AND FORECAST
SOUNDING SHOW SOME MODEST INSTABILITY WITH CAPES BETWEEN 1200-2000
J/KG. WEAK UPPER SUPPORT TO COMBINE WITH THE SURFACE ELEMENTS KEEP A
CHANCE OF RAIN ACROSS THE RIO GRANDE VALLEY. THE NORTHERN RANCH
LANDS ARE A BIT MORE REMOVED FROM THE FRONT LOWER THE CHANCE OF RAIN
THERE. PWATS REMAIN AROUND 2 INCHES SO SOME PASSING SHOWERS OR
STORMS WILL BE CAPABLE OF PRODUCING BRIEF HEAVY RAIN. ANOTHER ONE
HALF TO 1+ INCHES IN SOME LOCALIZED SPOTS CAN NOT BE RULED OUT.
AS FOR TEMPERATURES COOLER AIR BEHIND THE FRONT COUPLED WITH MOSTLY
CLOUDY TO CLOUDY SKIES TODAY AND THE WET GROUND WILL KEEP
TEMPERATURES BELOW NORMAL. WENT SLIGHTLY BELOW A MODEL BLEND.

TONIGHT AND MONDAY...WITH DAYTIME HEATING WANING ANY SHOWERS LEFT OVER
FROM THE AFTERNOON WILL BE WEAKENING DURING THE EVENING HOURS.
WILL MAINTAIN CHC TO SLIGHT CHC POPS ALONG THE RIVER COUNTIES
WHERE THE BOUNDARY AND DEEPER MOISTURE RESIDES. ALL EYES WILL THAN
BE FOCUSED ON THE TROPICAL WAVE MOVING ACROSS THE GULF OF MEXICO
AND ITS WEAK LOW PRESSURE AREA OVER SOUTHEAST OF NEW ORLEANS. THE
HURRICANE CENTER DOES NOT EXPECT ANY ORGANIZED DEVELOPMENT FROM
THIS SYSTEM WITH STRONG WINDS ALOFT ASSOCIATED WITH AN UPPER LEVEL
LOW THAT IS ALSO TRACKING WESTWARD. AS THESE SYSTEMS TRACK
WESTWARD WE WILL EXPECT SHOWERS AND STORMS TO DEVELOP OVERNIGHT
DURING A TYPICAL DIURNAL NIGHTTIME MAXIMUM. TIMING WILL BE
DIFFICULT WITH THE LOW TO APPROACH THE COAST SOMETIME MONDAY. POPS
HAVE BEEN INCREASED WITH MOST OF THE MODELS TRENDING UPWARD. THE
CONVECTION TO BLOSSOM OVER THE GULF WATERS AND TRACK WESTWARD. DO
NOT BELIEVE THE FRONT WILL PLAY A FACTOR ON MONDAY WITH THE
BOUNDARY LOSING MUCH OF ITS IDENTITY. AS THE WAVE APPROACHES
COASTAL TROUGHING DEVELOPS WHICH WILL FOCUS BETTER CONVERGENCE
ACROSS THE EASTERN ZONES EARLY AND AS THE UPPER LOW TRACKS FARTHER
WEST UPPER DIVERGENT FLOW INCREASES. A GOOD CHANCE OF RAIN IS IN
THE OFFERING ON MONDAY AND WENT SLIGHTLY HIGHER THEN THE MODEL
CONSENSUS. AGAIN MOISTURE CONTENT WILL BE INCREASING AND PWATS
INCHING ABOVE THE 2 INCH MARK. HEAVY RAIN CAN BE EXPECTED WITH
AMOUNTS OF 1-2 INCHES IN SPOTS. MONDAY`S TEMPERATURES WILL BE MORE
DIFFICULT TO GAUGE BUT THEY WILL LIKELY BE BELOW NORMAL.

LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...WEAK SURFACE LOW /
TROPICAL WAVE MOVING ACROSS THE GULF OF MEXICO WILL MOVE TOWARDS
OUR COAST AND COASTAL WATERS MONDAY NIGHT THEN INTO DEEP SOUTH
TEXAS TUESDAY THEN WEAKEN AS IT CONTINUES WESTWARD HEADED INTO
WEDNESDAY. MID LEVEL HIGH PRESSURE DRAPED ACROSS THE SOUTHEAST
CONUS WILL WEAKEN AND RETROGRADE TOWARDS THE DESERT SOUTHWEST AS A
SHORTWAVE TROUGH MOVES ACROSS THE EASTERN PACIFIC AND INTO THE
PACIFIC NORTHWEST WEDNESDAY INTO THURSDAY. A MINOR SHORTWAVE WILL
MOVE ACROSS THE ARKLATEX INTO THE SOUTHEAST CONUS TUESDAY AND
WEDNESDAY SUPPORTING A SFC LOW PRESSURE SYSTEM BEING PUSHED
SOUTHEASTWARD BY 1023MB SFC HIGH PRESSURE INTO THE MIDWEST. COLD
FRONT WILL MAKE IT TO THE NORTHERN GULF COAST AND INTO THE
NORTHEAST GULF THURSDAY AND FRIDAY BUT WILL HAVE LITTLE EFFECT ON
OUR WEATHER. INTO THE NEXT WEEKEND THE PACIFIC NORTHWEST TROUGH
MOVES ACROSS MUCH OF THE COUNTRY WHICH WILL SUPPORT ANOTHER COLD
FRONT INTO NORTHERN TEXAS. DETAILS AT THIS POINT ARE SKETCHY AT
BEST WITH BIG DIFFERENCES BETWEEN THE GFS AND ECMWF.

TROPICAL WAVE/TROUGHING/CONVERGENCE WILL KEEP SHOWERS AND
THUNDERSTORMS IN THE FORECAST TUESDAY WITH PWATS AOA 2.1 INCHES AND
WEDNESDAY AS WELL AS PWATS BEGIN TO SLOWLY LOWER TO 1.9 INCHES. WILL
MAINTAIN AND EXPAND 50 POPS ACROSS THE AREA TUESDAY AS THE TROPICAL
WAVE MOVES ASHORE. WEDNESDAY WILL KEEP HIGHEST POPS ACROSS THE
COASTAL WATERS WHERE COASTAL TROUGHING WILL PERSIST /50 POPS/ BUT
WILL LOWER POPS TO 40 PERCENT INLAND AS PWATS SLOWLY DECREASE AND
UPSTREAM HIGH PRESSURE NUDGES INTO THE AREA. MID LEVEL DRY AIR
INCREASES WITH TIME THURSDAY AND INTO THE WEEKEND AND SFC TROUGHING
WEAKENS AND LARGE SCALE SUBSIDENCE INCREASES. WILL MAINLY KEEP
SLIGHT CHANCE POPS OFFSHORE INTO THE WEEKEND BUT NOT SURPRISED IF A FEW
ISOLATED SHOWERS DEVELOP IN THE COASTAL COUNTIES.

MARINE...NOW THROUGH MONDAY...BROAD SURFACE HIGH PRESSURE OVER
THE SOUTHERN STATES EXTENDING INTO TEXAS IS MAINTAINING A
PERSISTENT NORTHEAST FLOW OVER THE COASTAL WATERS. HIGHER SWELLS
ASSOCIATED WITH THE LONG NORTHEAST ARE KEEPING A HIGH SEA OVER THE
FAR OFFSHORE COASTAL WATERS THIS MORNING. WILL BE EXTENDING THE
SMALL CRAFT ADVISORY FOR THE 20-60NM WATERS THROUGH THE MORNING.
THE GRADIENT WEAKENS SLIGHTLY AS THE SURFACE RIDGE MOVES EAST. THE
MODERATE NORTHEAST GRADIENT TO PERSIST AS A TROPICAL WAVE AND LOW
PRESSURE TROUGH TRACK ACROSS THE GULF APPROACHING THE LOWER TEXAS
MONDAY. SCATTERED SHOWERS AND THUNDERSTORMS TO CONTINUE TODAY
THROUGH MONDAY.

MONDAY NIGHT THROUGH THURSDAY...TROPICAL WAVE OR WEAK
SURFACE LOW WILL BE MOVING ACROSS THE COASTAL WATERS MONDAY NIGHT
AND INTO THE LAND AREAS TUESDAY. WINDS WILL BE AT THEIR HIGHEST
MONDAY NIGHT INTO EARLY TUESDAY /12 TO 15 KNOTS FROM THE EAST/ THEN
DECREASE THROUGH THURSDAY. GENERALLY SPEAKING LIGHT TO MODERATE
SOUTHEAST WINDS WILL PREVAIL TUESDAY THROUGH THURSDAY WITH SEAS 2-3
FEET. SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE THIS PERIOD SO
LOCALLY ADVERSE CONDITIONS COULD BE ENCOUNTERED UNDER HEAVY SHOWERS
OR THUNDERSTORMS.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT ADVISORY UNTIL 7 PM CDT THIS EVENING FOR GMZ170-175.

&&

$$

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