Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 141007
AFDBRO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
407 AM CST SUN DEC 14 2014

.SHORT TERM /NOW THROUGH MONDAY/...
MODEL IN GOOD AGREEMENT THAT THE APPROACHING MIDLEVEL TROUGH WILL
EJECT NEWD ACROSS THE CENTRAL US...DRAWING THE ASSOCIATED SFC LOW
PRESSURE FROM THE TEXAS PANHANDLE INTO SOUTHERN IOWA. THIS WILL KEEP
THE MIDLEVEL STEERING FLOW FROM DUE WEST...PUSHING AGAINST THE
ADVANCEMENT OF THE NEXT COLD FRONT. MODELS PICKED UP THE LLVL JET AT
H9 RACING NORTHWARD ACROSS THE WESTERN VALLEY ATTM...AND ARE
TRANSLATING THIS FEATURE TO THE EAST...SETTLING JUST OFFSHORE THIS
AFTERNOON. DECENT LLVL MIXING EXPECTED WILL HELP TO DRAW THE BREEZY
CONDITIONS TO THE SFC THIS AFTERNOON...WITH WINDS APPROACHING 20
KNOTS ALONG THE COAST. TONIGHT WINDS JUST OFF THE SFC TURN MORE
SWLY...DRAWING IN DRIER AIR. WINDS FROM THE SOUTH AT THE SFC WILL
KEEP GULF MOISTURE IN PLACE RIGHT AT THE SFC...SO HAVE SOME CONCERN
THAT FOG FORMATION WILL BE GREATER OVER A WIDER AREA. WITH THAT
SAID...SFC WINDS ARE NOT FORECAST TO DROP BELOW 5KTS...SO FOG SHOULD
NOT HAVE THE OPPORTUNITY TO BECOME OVERLY DENSE. ON MONDAY...THE
FRONT APPROACHES FROM THE NORTH...WITH MODELS DRAWING A PREFRONTAL
TROUGH INTO THE AREA EARLY IN THE DAY. THAT WILL KEEP WINDS LOWER
THAN TODAY. A FEW SHOWERS ARE BRIEFLY POSSIBLE DURING PEAK HEATING
TIMES MONDAY AFTERNOON ACROSS THE KING RANCH AREAS...BUT OVERALL
STILL TOO LITTLE INSTABILITY AND DRY AIR ALOFT FOR MORE WIDESPREAD
RAINFALL.

.LONG TERM /MONDAY NIGHT - SATURDAY/...GENERAL WEST-SOUTHWEST FLOW
ALOFT WITH PERIODIC FEEDS OF PACIFIC MOISTURE AND EMBEDDED
SYSTEMS...THE FIRST A DISSIPATING SURFACE FRONT LEFT BEHIND BY THE
WELL-TRAVELED AND IMPACTFUL PACIFIC COAST STORM WHICH MOVES INTO THE
UPPER MISSISSIPPI VALLEY MONDAY EVENING AS FLAT 500 MB RIDGE
REBUILDS OVER S. TEXAS AND NORTHERN MEXICO...AND THE SECOND A MORE
PROGRESSIVE AND HIGHER AMPLITUDE TROUGH THAT FLATTENS THE RIDGE AND
RACES ACROSS NORTH TEXAS THURSDAY NIGHT AND FRIDAY WHICH (CROSS
FINGERS) BRINGS LOW AND MID LEVEL DRY AIR AND PULLS TEMPERATURES
DOWN TO SEASONAL LEVELS FOR THE LAST SHOPPING WEEKEND PRIOR TO
CHRISTMAS.

AS ALWAYS WITH FAST FLOW PATTERNS THE DEVIL IS IN THE DETAILS...AND
CONFIDENCE IN EXACTLY HOW THE WEATHER WILL PLAY OUT IS ONLY MEDIUM
AT THIS POINT ESPECIALLY IF/WHEN/WHERE RAIN FALLS BEFORE THE MORE
SERIOUS DRY AIR ARRIVES BY THE END OF THE WORK WEEK.

FOR THE SENSIBLE WEATHER: MONDAY NIGHT...THE SURFACE FRONT OOZES
TOWARD THE NORTHERN RANCHLANDS BY DAYBREAK WITH AN EVENTUAL WIND
SHIFT TO THE NORTHEAST.  ECMWF IS MOST AGGRESSIVE WHILE THE NAM
LEAST AGRESSIVE AT FIRST AND THE GFS SITS IN THE MIDDLE. THE
GFS...WHICH HAS DONE FAIRLY WELL WITH THE GIST OF THE CURRENT
SUBTROPICAL FLOW PATTERN...MAY HAVE THE BEST HANDLE ON MONDAY
NIGHT`S THROUGH TUESDAY NIGHT`S WEATHER. AS THE FLAT RIDGE BUILDS
BROADLY IN THE 700-500 MB LAYER...THE FRONT SIDE /UPPER CONVERGENT/
OF THE RIDGE FAVORS THE INCREASING SURFACE PRESSURES...AS HIGH AS
1027 MB OVER N. TEXAS TUESDAY MORNING...WHICH SHOULD PUSH THE COOLER
AIR INTO THE NORTHERN RANCHLANDS EARLY IN THE DAY.

HOW FAR SOUTH THE COOLER AIR GETS REMAINS IN QUESTION...AND MAXIMUM
TEMPERATURES TUESDAY MAY BE HIGHLY DEPENDENT ON HEIGHT OF CLOUD
BASES AND STRENGTH OF NORTHEAST WIND. THE NAM-12...WHICH HAS DONE
QUITE WELL THIS SEASON WITH BOTH THE NOVEMBER ARCTIC OUTBREAK AND A
MORE TRICKY BUT STILL NOTABLE COOLING TEN DAYS AGO...HOLDS THE
COOLER AIR UP BEFORE REACHING THE POPULATION CENTERS OF THE VALLEY
WITH A FAIRLY SHARP DIFFERENCE IN AFTERNOON TEMPERATURES BETWEEN
MCALLEN (80+) AND FALFURRIAS (MID 60S). HAVE A HARD TIME THINKING
THAT THERE WON`T BE A FEW DEGREES SHAVED OFF TUESDAY`S HIGHS
COMPARED WITH TODAY AND MONDAY...AND GFS SEEMS TO PRESENT THE HAPPY
MEDIUM. AS FOR PRECIPITATION...SOUTHERLY FLOW BETWEEN 925 AND 700
SHOULD BRING ENOUGH MOISTURE AND THE FRONT JUST ENOUGH LIFT TO HOLD
ONTO THE CHANCE RANGE (30 PERCENT) ALONG AND JUST NORTH OF THE
BOUNDARY WITH SLIGHLY LOWER CHANCES ACROSS THE VALLEY...SO NO
CHANGES HERE.

THE SURFACE RIDGE SCOOTS INTO THE MISSISSIPPI VALLEY BY EARLY
WEDNESDAY AND SOUTHEAST FLOW RETURNS TO THE ENTIRE REGION OVERNIGHT
TUESDAY WHICH WILL KEEP TEMPERATURES FROM FALLING MUCH ACROSS THE
RANCHLANDS AND KEEP ABOVE AVERAGE READINGS...60S...ACROSS THE VALLEY
WITH PLENTY OF LOW CLOUDS TO INSULATE.

BY WEDNESDAY...THE MORE ROBUST PACIFIC TROUGH REACHES THE U.S. FOUR
CORNERS AND SHIFTS THE UPPER RIDGE AXIS TO THE CENTRAL GULF.
INCREASING SOUTHWEST FLOW ALOFT WILL AID INCREASING SOUTHERLY
BREEZES AND A MORE TROPICAL FEEL TO THE AIRMASS...AND WITH A MILD
START EXPECT UPPER 70S TO NOSE FARTHER NORTH...WITH LOWER OR EVEN
MID 70S RETURNING TO THE RANCHLANDS. WILL BE RAISING TEMPERATURES A
FEW DEGREES DESPITE THE CONSIDERABLE CLOUDS FOR MOST. WOULD NOT BE
SURPRISED TO SEE LATE NIGHT/MORNING FOG ACROSS THE RANCHLANDS WHERE
THE EVENING STARTS COOL BUT DEWPOINTS RISE TOWARD THE LOW
TEMPERATURE.  WILL LET LATER SHIFTS DECIDE WHEN/WHERE TO ADD. AS FOR
RAIN CHANCES...WILL BROAD BRUSH SLIGHT CHANCES /20 PERCENT/ FOR ALL
AREAS THOUGH CONFIDENCE IN NOTABLE RAIN IN MOST AREAS IS LOWERING
WITH FAIRLY THICK DRY AIR LAYER ABOVE BUILDING INVERSION AROUND 900
MB IN INCREASING SOUTHERLY FLOW. AS MENTIONED EARLIER...ECMWF
APPEARS TOO ROBUST WITH DEEPER MOISTURE THAT QUICKLY FADES OVER THE
RANCHES WEDNESDAY NIGHT.

THURSDAY LOOKS RELATIVELY WARM AND STICKY AS SOUTHERLY WINDS
CONTINUE. WARM LAYER SETS UP WITH INCREASING DOWNSLOPE FLOW ABOVE
THE INVERSION BASE AT 850 MB WHICH SHOULD PUT THE KIBOSH ON MOST
CONVECTION.  WILL KEEP MENTIONABLE CHANCES...BARELY (20 PERCENT) BUT
REMOVE THUNDER THROUGH THURSDAY DAYTIME. THE APPROACH OF THE
FLATTENING SYSTEM...THE FAVORED GFS SOLUTION...OVERNIGHT PROVIDES
THE BEST POSSIBILITY FOR THUNDER. BUT ATMOSPHERIC PROFILE /REALLY/
DRIES OUT ESPECIALLY ABOVE 700 MB (WITH PLENTY OF CIRRUS ABOVE) AND
CONFIDENCE IS WANING ON ANY PRECIPITATION AHEAD OF THE ACTUAL
SURFACE FRONT. BECAUSE LAPSE RATES ARE MARGINALLY FAVORABLE AND
WE`RE LOOKING AT A DAY FIVE FORECAST WILL LEAVE THE MENTION IN BUT
REDUCE CHANCES TO SLIGHT CHANCE /20 PERCENT/ FOR NOW.

THE WIND SHIFT ARRIVES FRIDAY MORNING AND LOW TO MID LEVEL DRY AIR
FINALLY ARRIVES. FILTERED SUNSHINE THROUGH CIRRUS SHOULD PUSH
EASTWARD FROM THE RIO GRANDE PLAINS/RANCHLANDS INTO THE MID/UPPER
VALLEY BY AFTERNOON...PROBABLY REACHING THE LOWER VALLEY BEFORE
SUNSET.  WITH AIRMASS STILL WARM-ISH WILL KEEP TEMPERATURES ON THE
HIGH SIDE...UPPER 70S TO NEAR 80 VALLEY AND MID TO UPPER 70S
RANCHLANDS.  THE COOLING ARRIVES FRIDAY NIGHT UNDER FILTERED
CIRRUS...AND CURRENT FORECAST TEMPERATURES AT SEASONAL VALUES
/MID-UPPER 40S RANCHES AND LOWER 50S VALLEY/ LOOK ON TRACK.

SATURDAY LOOKS TO BE THE WINNING DAY OF THE LOT IF THE DAY SEVEN
FORECAST CAN HOLD.  AIR MASS NOT ALL THAT COOL...AND WITH 850 MB
TEMPERATURES IN THE +10 TO +12 RANGE EXPECT HIGHS TO REACH THE LOWER
70S IN MANY AREAS...PERHAPS AROUND 70 BROOKS COUNTY...AND WILL RAISE
ACCORDINGLY.


&&

.MARINE...NOW THROUGH SUNDAY NIGHT...WINDS OFFSHORE ARE HOVERING IN
THE 15 TO 20 KNOT RANGE CURRENTLY...AND WILL REMAIN MODERATE THROUGH
THIS AFTERNOON INTO TONIGHT. SMALL CRAFT ARE ADVISED TO EXERCISE
CAUTION TODAY AND TONIGHT FOR ALL MARINE ZONES. SEAS WILL GRADUALLY
INCREASE TO NEAR 5 FEET BY THIS EVENING. THE APPROACH OF THE NEXT
FRONT JUST  TO THE NORTH WILL ALLOW WINDS TO RELAX DURING THE DAY
MONDAY...WITH SEAS SLOWLY FALLING DOWN TO 3 FEET DURING THE
AFTERNOON.

MONDAY NIGHT THROUGH THURSDAY:  APPROACH OF FRONT WILL SLACKEN WINDS
AND DROP SEAS MONDAY NIGHT...WITH MODERATE NORTHEAST WINDS PROBABLY
REACHING CAUTION LEVELS /15 TO 20 KNOTS/ ARRIVE ACROSS THE WATERS
NORTH OF PORT MANSFIELD BY TUESDAY MORNING.  WIND SPEEDS COULD BE
SEVERAL KNOTS LOWER EAST OF CAMERON COUNTY...SO MAY SEPARATE COASTAL
ZONES INTO A NORTH/SOUTH SPLIT TO COVER DIFFERENCES.

WINDS VEER AROUND TO THE SOUTHEAST TUESDAY NIGHT AND WEDNESDAY AND
GRADUALLY INCREASE.  WITH MARINE LAYER A BIT MORE NOTABLE WITHIN THE
NEARSHORE WATERS WILL SHADE SPEEDS DOWN WEDNESDAY THROUGH THURSDAY
HERE WITH CAUTION LEVELS EDGING INTO BOTH THE OFFSHORE AND LAGUNA
WATERS.  SEAS WILL INCH UP TO 5 FEET WITH LOCALLY HIGHER LEVELS AS
WELL BEGINNING WEDNESDAY AND CONTINUING THURSDAY.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  77  67  78  66 /  20  10  10  20
BROWNSVILLE          78  66  80  66 /  20  10  10  20
HARLINGEN            79  65  81  64 /  20  10  10  20
MCALLEN              81  65  81  64 /  10  10  10  20
RIO GRANDE CITY      81  63  80  64 /  10  10  10  20
SOUTH PADRE ISLAND   76  68  76  67 /  20  10  10  20

&&

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

$$

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

SHORT TERM...64/JS
LONG TERM...52/BSG
MARINE...64/52
GRAPHICASTS/PUBLIC SERVICE UNIT...CAMPBELL





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