000
FXUS64 KBRO 051242
AFDBRO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
642 AM CST THU DEC 5 2013

.DISCUSSION...CANCELLED THE DENSE FOG ADVISORY AS VISIBILITIES
OVER THE PAST TWO HOURS IN THE ADVISORY WERE ABOVE CRITERIA. AREAS
OF FOG CONTINUE ACROSS THE MIDDLE AND UPPER VALLEY AND HAVE
HANDLED THIS WITH A NOWCAST THROUGH 9AM. DFA REMAINS OVER THE
COASTAL AREAS. UPDATE AND GRIDS SENT.

&&

.PREV DISCUSSION... /ISSUED 532 AM CST THU DEC 5 2013/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...DENSE FOG HAS BEEN ONGOING ACROSS THE VALLEY AND DEEP
SOUTH TEXAS WITH LIFR AND IFR CONDS AT THE TAF SITES. EXPECT THIS
TO CONTINUE THROUGH MID MORNING WITH A SLOW IMPROVEMENT TO MVFR BY
LATE MORNING AND BRIEFLY TO VFR THIS AFTERNOON BEFORE DROPPING DOWN
TO IFR AND BELOW EARLY THURSDAY EVENING. WINDS WILL BE FROM THE
SOUTHEAST EARLY IN THE TAF PERIOD MORE EASTERLY LATE IN THE
AFTERNOON THEN NORTHEASTERLY OVERNIGHT. A COLD FRONT WILL MOVE
INTO THE AREA THIS AFTERNOON WILL ISOLATED SHOWERS AFTER 00Z.

PREV DISCUSSION... /ISSUED 410 AM CST THU DEC 5 2013/

SHORT TERM.../NOW THROUGH FRIDAY/...COMPLICATED WEATHER SCENARIO
FOR THE SHORT TERM PERIOD WITH A MYRIAD OF CHALLENGES INCLUDING
DENSE FOG THIS MORNING...TIMING OF THE ARCTIC COLD FRONT...AND
TEMPERATURES THROUGHOUT THE SHORT TERM.

WATER VAPOR IMAGERY THIS MORNING SHOWED A RIDGE ACROSS THE EASTERN
PACIFIC WITH A DEEPENING TROUGH OVER THE WESTERN CONUS. MID LEVEL
HIGH PRESSURE IS ALSO HANGING TOUGH ACROSS THE SOUTHERN GULF OF
MEXICO WITH RIDGING ACROSS THE EASTERN SEABOARD. A 160KT JET MAX IS
LOCATED ACROSS THE NORTHERN PLAINS DOWNSTREAM FROM THE LONGWAVE
TROUGH AXIS WITH 110KT JET MAX DIVING DOWN THE BACKSIDE OF THE
TROUGH. AT THE SURFACE...COLD FRONT IS LOCATED FROM TEXARKANA TO
NORTH OF AUSTIN TO SOUTH OF SAN ANGELO AT 08Z. FOG IS WIDESPREAD
SOUTH AND EAST OF THIS FRONT INCLUDING HERE IN DEEP SOUTH TEXAS.

EXPANDED DENSE FOG THIS MORNING TO INCLUDE CAMERON...WILLACY...JIM
HOGG...AND BROOKS COUNTIES AS SURFACE OBSERVATIONS AND AREA WEBCAMS
SHOW DENSE FOG IN THESE LOCATIONS. ALSO...EXTENDED THE EXPIRATION
TIME TO 15Z AND WILL MONITOR FOR POSSIBLE EXTENSION A LITTLE LONGER.
FOR HIDALGO...STARR...AND ZAPATA WILL USE NOWCASTS AS FOG HAS NOT
BEEN AS DENSE BUT WILL MONITOR FOR POSSIBLE INCLUSION IF CONDITIONS
WARRANT.

COLD FRONT CONTINUES TO MOVE QUICKER THAN MODELS HAVE INDICATED AND
THIS MAKES FOR A TRICKY FORECAST IN THE SHORT TERM. BASED ON THE
TRACK RECORD AND HISTORY...BELIEVE NAM HAS THE BETTER IDEA WITH RAP
MODEL LENDING CREDENCE AND HAVE LEANED TOWARD THIS MODEL IN THE SHORT TERM.
FRONT WILL ENTER THE RANCHLANDS AND BRUSH COUNTRY EARLY THIS
AFTERNOON THEN SLOW DOWN AS THE SYSTEM BUMPS AGAINST THE MID LEVEL
HIGH AND SHORTWAVE ENERGY ROUNDS THE BASE OF THE TROUGH. ONCE THE
SHORTWAVE EMERGES ACROSS NORTHERN MEXICO THIS WILL HELP PUSH THE
FRONT DOWN SOUTH OF THE AREA AND ALLOW RIDGING FROM A 1042MB HIGH
PRESSURE OVER THE NORTHERN PLAINS TO FULLY INFILTRATE THE AREA.

WITH THE EARLIER ARRIVAL OF THE FRONT INTO THE RANCHLANDS...MET AND
MAV GUIDANCE HAVE CAME IN COOLER. IN FACT...MET GUIDANCE CAME IN 12
DEGREES COOLER FOR KHBV FOR A HIGH TODAY. WENT AHEAD AND LOWERED
HIGHS UP ACROSS ZAPATA...JIM HOGG...AND BROOKS COUNTIES BUT NOT
QUITE AS LOW AS MET GUIDANCE. IF ANYTHING ELSE I AM CLOSER TO THE
MAV GUIDANCE. DOWN IN THE VALLEY WE WILL HAVE MOST OF THE DAY OF
WARMING AND DID NOT ADJUST HIGHS MUCH AT ALL FOR TODAY. TEMPERATURES
NOSE DIVE FROM NORTH TO SOUTH LATER TODAY THROUGH FRIDAY. HIGHS
FRIDAY WILL BE SOME 25-40 DEGREES COOLER THAN THURSDAY. NEEDLESS TO
SAY...ITS TIME TO GET OUT THE HEAVIER JACKETS AND BUNDLE UP THE KIDS
FOR SCHOOL.

PRECIPITATION WISE WILL KEEP GRIDS AS IS. MOST PRECIPITATION WILL
HOLD OFF TILL AFTER 00Z WITH AN ISOLATED THUNDERSTORM POSSIBLE
THURSDAY NIGHT AND FRIDAY MORNING BEFORE STRATIFORM PRECIPITATION
TAKES OVER FRIDAY AFTERNOON. UNLESS UNDER A THUNDERSTORM...RAINFALL
AMOUNTS WILL BE LIGHT.

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...EVOLUTION OF UPPER
AIR PATTERN REMAINS ON TRACK TO LOCK IN A COUPLE OF SURGES OF
ARCTIC AIR TO THE RIO GRANDE VALLEY. THE FIRST WILL ALREADY
THROUGH THE REGION FRIDAY NIGHT WITH THE NEXT SURGE ON MONDAY.
WINTER WEATHER HIGHLIGHT DURING THIS PERIOD WILL BE VERY LOW WIND
CHILLS...LIGHT FREEZE OVER THE RANCH LANDS AND A SMALL CHANCE OF
SOME SLEET MIXING IN WITH LIGHT RAIN SATURDAY ALSO ACROSS THE
RANCH LANDS.

COLD AIR ADVECTION TO PEAK SATURDAY WITH A STRENGTHENING LOW LEVEL
INVERSION. SOUTHERLY FLOW ABOVE THE INVERSION STRENGTHENS AS A
THE POSITIVELY TILTED UPPER TROUGH OVER THE ROCKIES DEEPENS. ISENTROPIC
LIFT MAXIMIZES SATURDAY WITH A CHANCE OF RAIN AND PREDOMINATE
DRIZZLE. POINT SOUNDINGS CONTINUE TO SHOW A SATURATED LAYER OF
AROUND 1500 FEET DEEP DIPPING BELOW FREEZING ACROSS THE NORTHERN
RANCHLANDS. THIS SUGGEST THAT A MIX OF SLEET WITH THE RAIN IS
POSSIBLE LATE FRIDAY NIGHT INTO SATURDAY MORNING. HAVE NOT
INDICATED THIS IN THE GRIDS JUST YET AND WILL WAIT ANOTHER PERIOD
OR TWO TO SEE HOW MUCH COLD DOES MAKE IT THIS FAR SOUTH. IN ANY
CASE SURFACE TEMPERATURES TO REMAIN ABOVE FREEZING WHICH WILL
ALLOW FOR ANY SLEET TO MELT RATHER QUICKLY ON CONTACT. OTHER WISE
WITH NO SUN AND THE LOW OVERCAST AND PRECIP TEMPERATURES WILL
STRUGGLE TO BREAK 40 DEGREES IN THE NORTH AND 45 AT THE COAST.
FINALLY WITH THE STRONG NORTH WINDS WIND CHILL ADVISORIES ARE
LOOKING MORE PROBABLE FOR FRIDAY NIGHT INTO SATURDAY MORNING.

A BRIEF REPRIEVE STILL IN ORDER SUNDAY AS THE NEXT SURGE TAKES
SHAPE OVER THE ROCKIES. SLOW IMPROVEMENT IN TEMPERATURES WITH MOST
OF DRIZZLE ENDING WITH EXCEPTION TO THE COASTAL AREAS. SECOND
FRONT TO MOVE THROUGH MONDAY LATE MORNING EARLY AFTERNOON.
PRESSURE GRADIENT TO STRENGTHEN AS 1039MB HIGH INTERACTS WITH
LOWER PRESSURE OFFSHORE. TEMPERATURES TO FALL DURING THE AFTERNOON
AS WINDS PICK UP BECOMING BLUSTERY. BOTH GFS/ECMWF INCREASE POPS
MONDAY WITH A STRONGER COASTAL LOW DEVELOPING. FORECAST HAS BEEN
ADJUSTED TO SHOW STRATIFORM RAIN DEVELOPING ALONG WITH DRIZZLE
ONCE AGAIN. SURFACE RIDGE BUILDS FAR ENOUGH SOUTH BY TUESDAY
PARTIALLY CLEARING SKIES. TEMPERATURES PLUMMET MONDAY NIGHT WITH
PROBABILITIES OF FREEZING CONDITIONS ESPECIALLY NORTH AND WEST
INCREASING. STILL A COLD DAY ON TUESDAY WITH CAA ADVECTION
CONTINUING. ANOTHER SHORTWAVE IS INDICATED TO MOVE INTO WEST TEXAS
WEDNESDAY WITH CLOUDS ONCE AGAIN INCREASING AND A SLOW RECOVERY OF
TEMPERATURES.

MARINE...NOW THROUGH FRIDAY...A COLD FRONT WILL MOVE INTO THE
COASTAL WATERS THIS AFTERNOON AND EXIT TO THE SOUTH FRIDAY
MORNING. MARINE CONDITIONS WILL BEGIN TO DETERIORATE OVERNIGHT
WITH STRONG NORTHERLY WINDS FRIDAY AND SEAS INCREASING TO AROUND
10 FEET BY FRIDAY AFTERNOON. A FEW GALE FORCE GUSTS CANNOT BE
RULED OUT WITH SOLID SMALL CRAFT ADVISORIES CONDITIONS BEGINNING
LATE THURSDAY NIGHT.

MARINE CONDITIONS FRIDAY NIGHT AND SATURDAY WILL CONTINUE TO
ADVERSE WITH SOME GALE FORCE GUSTS CONTINUING INTO SATURDAY
MORNING. A BRIEF DROP IN WINDS AND SEAS SUNDAY MAY BE ENOUGH TO
DROP ANY SCA THAT WILL BE IN EFFECT. A STRONGER NORTH SURGE
DEVELOPS MONDAY WITH A BETTER WINDOW FOR GALE CONDITIONS.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...DENSE FOG ADVISORY UNTIL 9 AM CST THIS MORNING FOR TXZ251-256-
     257.

GM...DENSE FOG ADVISORY UNTIL 9 AM CST THIS MORNING FOR GMZ130-132-
     135-150-155.

&&

$$

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HTTP://WEATHER.GOV/RGV

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