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000
FXUS64 KBRO 121111 AAA
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
511 AM CST THU DEC 12 2013

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

&&

.AVIATION...MVFR CONDITIONS PREVAIL THIS MORNING UNDER OVERCAST
SKIES AND LIGHT TO MODERATE NORTH WINDS. SPOTTY LIGHT RAIN IS
OBSERVED AT TIMES. MOISTURE WILL GET PUSHED TO THE SOUTH BY HIGH
PRESSURE FILTERING IN...BUT AN INVERSION WILL REMAIN AS WILL OVC
HIGH MVFR CEILINGS. WINDS WILL DECREASE TO VERY LIGHT TONIGHT
BEFORE SETTING UP FROM THE SOUTHEAST TO SOUTH ON FRIDAY.

&&

.PREV DISCUSSION... /ISSUED 337 AM CST THU DEC 12 2013/

SHORT TERM /TODAY THROUGH FRIDAY/...REINFORCING HIGH PRESSURE WILL
FILTER INTO THE CWA FROM THE NORTH TODAY...WITH LITTLE OVERALL
CHANGE FROM YESTERDAY. TEMPERATURES WILL BE MAINLY IN THE 50S UNDER
CLOUDY SKIES WITH LIGHT NORTH WINDS. MODIFICATION WILL OCCUR AS HIGH
PRESSURE TO THE NORTH SHIFTS EAST AND WINDS BEGIN TO VEER TONIGHT.
OVERNIGHT LOW TEMPS WILL DROP ONLY A FEW DEGREES INTO THE UPPER 40S
TO MID 50S WITH LIGHT WINDS. ON FRIDAY...SOUTHEAST WINDS WILL BECOME
ESTABLISHED WITH HIGH TEMPS SHOOTING UP INTO THE 60S AND 70S. CLOUDS
WILL LIFT HIGHER ON MODERATE SOUTHEAST WINDS...BUT IT WILL LIKELY
STILL REMAIN OVERCAST UNDER A LINGERING ELEVATED INVERSION. A SLIGHT
CHANCE OF RAIN WILL REMAIN IN THE FORECAST FOR FRIDAY AS A MID LEVEL
TROUGH THAT ORIGINATED NEAR SOUTHERN CALIFORNIA MOVES EAST ACROSS
NORTH TEXAS. MOST OF THE ENERGY FROM THE TROUGH WILL BE FOCUSED
NORTH OF THE RGV.

LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
LOW LEVEL SOUTHEASTERLIES WILL BEGIN TO DIMINISH THROUGH THE
OVERNIGHT FRIDAY AS A COLD FRONT PUSHES THROUGH CENTRAL TEXAS. WITH
MOISTURE POOLING AHEAD OF THE FRONT AND WINDS SLACKENING INTRODUCED
AREAS OF FOG MAINLY EAST OF A LINE FROM RIO GRANDE CITY TO
HEBBRONVILLE. TEMPERATURES SHOULD BE FAIRLY MILD WITH INCREASED
MOISTURE...RAIN CHANCES SEEM PRETTY SLIM WITH THE MAIN MID AND UPPER
LEVEL FORCING WELL TO THE NORTHEAST OF THE AREA.

NAM12 GUIDANCE IS A LITTLE FASTER THAN THE GFS/ECMWF WITH THE COLD
FRONT ON SATURDAY BUT NOT BY A LOT CALLING FOR A 18Z FROPA IN THE
MIDDLE AND LOWER VALLEY. WITH THE SHALLOW CENTRAL PLAINS HIGH
PRESSURE FORCED AIR MASS WILL WORK TO STAY OUT FRONT OF THE MODELS
AND SHIFTED THE FROPA ABOUT 4 HOURS FASTER IN THE NEW FORECAST
BRINGING THE INITIAL WIND SHIFT THROUGH ABOUT 14-15Z/8-9 AM. THE
850MB FRONT MORE CLOSELY ASSOCIATED WITH THE DIGGING LONG WAVE TROUGH
DIVING INTO THE BIG BEND REGION DOES NOT CLEAR UNTIL AROUND 00Z.
THAT PASSAGE IS SIGNALED AT THE SURFACE BY A PRONOUNCED INCREASE IN
SURFACE WIND SPEEDS AND NUDGED THAT UP IN THE GRIDS TO AROUND
21Z/3PM. RAINFALL CHANCES LOOK THE BEST BETWEEN THE SURFACE FROPA
AND THE 850MB FRONT...WHICH SUBSTANTIALLY CLEARS THE LOWER
TROPOSPHERE OF MOISTURE AND SIGNALS THE END OF ISENTROPIC LIFT.
NAM/GFS FORECAST SOUNDINGS SHOW WEAKER LOW LEVEL INSTABILITY THAN
PREVIOUS RUNS...WITH THE BEST MID LEVEL LIFT TRENDING TOWARDS
CENTRAL TEXAS SO REMOVED THUNDER MENTION FROM LAND AREAS FAVORING
SCATTERED SHOWERS AND PERIOD OF OVERRUNNING PRECIP. DAYTIME MAXIMUMS
ON SATURDAY SHOULD BE HELD IN CHECK BY THE EARLY FRONTAL PASSAGE AND
KEPT HIGHS TO AROUND 70 ALONG THE BORDER AND IN THE MID 60S FURTHER
NORTH...TEMPS WILL PROBABLY BEGIN TO TRAIL OFF BY 2 TO 3 PM.

WINDS WILL ALSO BE A FRONT SEAT CONCERN...ESPECIALLY OVER MARINE
AREAS. THE PLAINS SFC RIDGE IS 1032MB...TRENDING UPWARD...IN 00Z
GUIDANCE WITH STRONG MID AND UPPER LEVEL CONVERGENCE BEHIND THE
FRONT WITH GOOD MID AND LOWER LEVEL SUPPORT BACKING THE FRONT. SREF
GUIDANCE SHOWS CATEGORICAL PROBABILITY OF SUSTAINED WINDS AT 25KTS
OVER THE MARINE ZONES WITH NAM/GFS/ECWMF DETERMINISTIC GUIDANCE ALSO
SUGGESTIVE OF A 28G37KT TYPE MARINE EVENT. WHICH GIVEN THE SYNOPTIC
PATTERN SEEMS REASONABLE. THE ONLY CAVEAT WOULD BE THE COLD WATER
TEMPERATURES...ABOUT 55 DEGREE WITHIN 5 MILES OF THE COAST...WHICH
COULD LIMIT MECHANICAL MIXING...BUT FREQUENT GALE FORCE GUSTS LOOK
LIKE A GOOD POSSIBILITY...ESPECIALLY OFFSHORE WITH THIS EVENT.

SOME LINGERING MID LEVEL SHOWERS MAY CONTINUE TO SQUEAK OUT THROUGH
EARLY SUNDAY WITH THE UPPER LEVEL TROUGH NOT CLEARING UNTIL AROUND
MIDDAY. THAT TROUGH SHOULD KEEP CLOUD COVER AND PERSISTENT COLD AIR
ADVECTION IN PLACE THROUGH THE DAY. TRENDED LOWS DOWN A LITTLE
SUNDAY NIGHT AS WELL BUT DID NOT GO TOO BONKERS WITH TEMPS AS THE
SOURCE AIR MASS FOR THIS SYSTEM IS THE FRONT RANGE OF THE ROCKIES IN
COLORADO AND NOT THE DEEP ICEBOX OF EASTERN ALASKA AND THE NORTHWEST
TERRITORIES OF CANADA.

MONDAY...SURFACE HIGH PRESSURE BEGINS TO ESTABLISH FROM SOUTHWEST TO
NORTHEAST ACROSS THE WESTERN GULF COAST. WITH CONVERGENCE OVERHEAD
AND BUILDING LOW LEVEL HIGH PRESSURE EXPECT TO SEE MORE SUN THAN WE
HAVE BEEN ACCUSTOMED TOO LATELY WITH TEMPERATURES REBOUNDING TO MORE
SEASONABLE LEVELS. THAT SAME TREND IS EXPECTED TO BUILD THROUGH
TUESDAY AND WEDNESDAY WITH SURFACE HIGH PRESSURE SHIFTING EASTWARD
DRIVING SOUTHEASTERLY LOW LEVEL RETURN FLOW THROUGH THE END OF
THE FORECAST PERIOD. THE 00Z GFS BUILDS A RIDGE OVER THE CENTRAL
PLAINS WEDNESDAY INTO THURSDAY FORCING A COLD FRONT INTO THE AREA...BUT
AMONGST GFS ENSEMBLE MEMBERS AND THE ECMWF IT IS AN OUTLIER. THE GFS
IS MUCH MORE AMPLIFIED WITH A UPPER MISSISSIPPI VALLEY TROUGH THAT
GETS PINCHED IN BETWEEN AN EAST COAST AND WEST COAST TROUGH AND
PREFER THE ECMWFS MORE ZONAL APPROACH AND REFLECTED THAT IN THE
FORECAST.

MARINE...
FRIDAY NIGHT THROUGH MONDAY... FAVORABLE MARINE CONDITIONS ARE
EXPECTED MOST OF THE NIGHT ON FRIDAY WITH SLACKENING SOUTHEASTERLY
WINDS BECOMING EASTERLY. AREAS OF FOG WILL HOWEVER BE POSSIBLE. A
COLD FRONT IS EXPECTED TO MOVE ACROSS THE LOWER TEXAS COAST
SATURDAY MORNING WITH A REINFORCING SURGE OF NORTHERLY WINDS BY
SATURDAY AFTERNOON. STRONG NORTH WINDS ARE EXPECTED OVER ALL OF
THE LOWER TEXAS COAST SATURDAY INTO SATURDAY NIGHT AND SUNDAY
MORNING. CONDITIONS WILL BE AT LEAST SMALL CRAFT ADVISORY LEVELS
WITH FREQUENT GALE FORCE GUSTS POSSIBLE. A GALE WATCH MAY BE
ISSUED LATER TODAY OR FRIDAY MORNING. SEAS WILL ALSO BE VERY ROUGH
THROUGH SUNDAY BEFORE CONDITIONS BEGIN TO IMPROVE SUNDAY NIGHT
INTO MONDAY MORNING. MUCH MORE FAVORABLE CONDITIONS ARE EXPECTED
ON MONDAY WITH NORTHEAST WINDS BECOMING SOUTHEASTERLY LATE IN THE
DAY.

TODAY THROUGH FRIDAY...STRONG HIGH PRESSURE STRETCHING FROM TEXAS TO
THE OHIO VALLEY WILL SHIFT EAST UNDER AN ADVANCING MID LEVEL RIDGE.
MEANWHILE...PRESSURE WILL DECREASE OVER THE SOUTHERN PLAINS AS A MID
LEVEL LOW OVER SOUTHERN CALIFORNIA OPENS UP AND BEGINS TO MOVE EAST.
THE RESULT WILL BE A SLOW DECREASE IN NORTHEAST WINDS TODAY...WITH
MODERATE SEAS AND SMALL CRAFT EXERCISE CAUTION CONDITIONS EARLY ON
TODAY. WINDS WILL DECREASE TO LIGHT TONIGHT AS THEY START VEERING TO
EAST...AND THEN SOUTHEAST ON FRIDAY...WHEN THEY WILL ALSO INCREASE
TO MODERATE STRENGTH AGAIN.

&&

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

$$

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

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