Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 151745
AFDBRO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
1145 AM CST MON DEC 15 2014

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

&&

.AVIATION...CEILINGS HAVE BEEN SLOWLY RISING THIS MORNING ACROSS
MUCH OF THE REGION WITH THE EXCEPTION OF THE FAR WESTERN BRUSH
COUNTRY WHERE IFR/LIFR CONDITIONS REMAIN. MVFR CONDITIONS ACROSS
THE MID VALLEY SHOULD BECOME VFR EARLY THIS AFTERNOON AND REMAIN
SO UNTIL LATER TONIGHT. A COLD FRONT WILL ENTER THE AREA TONIGHT
AND MAKE IT INTO THE VALLEY LATE IN THE PERIOD. CALM TO LIGHT
WINDS AHEAD OF THE FRONT WILL ALLOW FOG TO DEVELOP AFTER 06Z AT
LOCAL TERMINALS...WITH LIFR CONDITIONS BY 09Z.

&&

.PREV DISCUSSION... /ISSUED 528 AM CST MON DEC 15 2014/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...CURRENT SATELLITE AND SURFACE OBSERVATIONS SHOW
IFR/LIFR IN THE MID VALLEY AT MFE AND NORTHWARD INTO THE
RANCHLANDS AND BRUSH COUNTRY OF SOUTH TEXAS. EXPECT THIS TO
CONTINUE THROUGH MID MORNING WITH CIGS RAISING TO VFR BY 16Z.
SOUTHEAST WINDS WILL BE LIGHT TO MODERATE WITH WIND SPEEDS
DROPPING OFF AFTER SUNSET. COLD FRONT WILL ENTER OUR AREA TONIGHT
AND MAKE IT INTO THE VALLEY LATE IN THIS FORECAST. WIND SPEEDS
WILL BE LIGHT AND AFTER 6Z EXPECT FOG TO DEVELOP AT THE TAF SITES.
AM EXPECTING CONDS TO BECOME IFR BY 6Z AND LIFR BY 9Z.

PREV DISCUSSION... /ISSUED 358 AM CST MON DEC 15 2014/

SHORT TERM /NOW THROUGH TUESDAY/...NEARLY VERTICALLY STACKED LOW
PRESSURE LOCATED OVER SOUTHERN KANSAS WITH THE SURFACE COLD FRONT
ACROSS WESTERN OKLAHOMA STRETCHING SOUTHWESTWARD INTO SOUTHWESTERN
TEXAS. LOW CLOUDS AND PATCHY FOG DEVELOPING EARLY THIS MORNING
ACROSS PORTIONS OF DEEP SOUTH TEXAS WITH WINDS MAINLY OUT OF THE
SOUTHEAST AND TEMPERATURES IN THE LOWER 60S ACROSS THE RANCHLANDS
TO AROUND 70 DEGREES IN THE VALLEY. CURRENT FORECAST LOWS LOOK
REASONABLE AND NO CHANGES NEEDED.

COLD FRONT WILL MAKE ITS WAY INTO DEEP SOUTH TEXAS THIS EVENING.
AHEAD OF THIS FEATURE...WINDS WILL BE MUCH LIGHTER AS COMPARED TO
SUNDAY WITH A PREFRONTAL TROUGH KEEPING WINDS ON THE LIGHTER SIDE.
ANY FOG IN THE AREA WILL DISSIPATE BY MID MORNING LEAVING BEHIND A
PARTLY TO MOSTLY CLOUDY SKY. HIGHS TODAY WILL REACH THE UPPER 70S IN
THE RANCHLANDS TO AROUND 80 DEGREES IN THE VALLEY.

AS THE FRONT EDGES IN...WEAK SURFACE CONVERGENCE MAY BE ENOUGH WITH
MOISTURE POOLING AHEAD OF THE FRONT TO SPARK A FEW SHOWERS AS THE
FRONT MOVES SOUTHWARD TONIGHT. HOWEVER...COVERAGE SHOULD BE FEW AND
FAR BETWEEN WITH WESTERLY LOW/MID LEVEL DRY FLOW AND LITTLE UPPER
SUPPORT. RAINFALL AMOUNTS SHOULD BE LIGHT. BEST SHOT WILL BE COASTAL
COUNTIES AND COASTAL WATERS.

FOG WILL BE MORE OF A CONCERN MONDAY NIGHT AND TUESDAY MORNING SOUTH
OF THE FRONT WHERE MOISTURE WILL BE THE HIGHEST AND WINDS WILL BE
NEARLY CALM. NAM/GFS BOTH PICK THIS UP AND SEEMS REASONABLE SO HAVE
INCLUDED A HIGHER COVERAGE OF FOG 9Z-15Z ACROSS THE VALLEY AREAS. MY
ONLY CONCERNS ARE ANY RESIDUAL CLOUD COVER RESTRICTING FULL
RADIATIONAL COOLING BUT THE LIGHT WINDS TO 10K FEET ARE HARD TO
IGNORE. PLUS ANY PRECIPITATION AROUND AHEAD OF THE FRONT. WILL GO
WITH AREAS AT THIS TIME BUT DENSE FOG APPEARS TO BE A POSSIBILITY IN
THE VALLEY.

FRONT SHOULD LIE JUST SOUTH OF THE VALLEY AFTER DAYBREAK. MODELS
CONTINUE TO POINT TO ISENTROPIC LIFT AND LIGHT RAIN AND SHOWERS JUST
NORTH OF THE FRONT MAINLY IN THE VALLEY FOR TUESDAY. DEPTH OF
MOISTURE LOOKS TO INCREASE BY TUESDAY AFTERNOON SO HAVE EDGED POPS
UP SLIGHTLY AND HAVE HIGHEST POPS IN THE VALLEY AND ALONG THE RIVER
TUESDAY AFTERNOON.

LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...THE FRONTAL BOUNDARY
WILL BEGIN TO RETURN NORTHWARD AND DISSIPATE BY WEDNESDAY MORNING
AS ELONGATED SFC RIDGE SHIFTS EWD TO THE MISSISSIPPI VALLEY.
DECENT SWLY SETS UP AS THE NEXT H5 TROUGH DIVES DOWN THE WEST
COAST. THIS WILL SET UP ISENTROPIC UPGLIDE ACROSS THE
AREA...ESPECIALLY FOR THE WESTERN VALLEY. RAIN CHANCES WILL REMAIN
LOW...WITH ONLY MINIMAL ACCUMULATION EXPECTED. SOUTHEAST SFC FLOW
WILL GENERALLY COUNTERACT THE DENSER CLOUD COVER...ALLOWING TEMPS
TO RISE INTO THE 70S WEDNESDAY THROUGH FRIDAY.

FRIDAY IS A PARTICULARLY DIFFICULT FORECAST...AS MINOR DIFFERENCES
IN MODEL OUTPUT HAVE BROUGHT SIGNIFICANT DIFFERENCES IN THE
FORECAST OUTCOME. THE NEXT H5 TROUGH WILL RACE ACROSS TEXAS
FRIDAY...INDUCING LEE SFC LOW DEVELOPMENT. GFS EJECTS THE MAIN
CORE OF THE H5 LOW AND ASSOCIATED SFC LOW FURTHER NORTH INTO
OKLAHOMA...WITH SLOWER ARRIVAL OF THE NEXT FRONT AROUND THE SFC
LOW FRIDAY NIGHT AROUND MIDNIGHT. ECMWF PULLS THE H5 LOW MUCH
FARTHER SOUTHWARD INTO TEXAS AND NORTH MEXICO...WITH LEE SFC LOW
DEVELOPING ACROSS SOUTH TEXAS AND EJECTING NEWD FRIDAY MORNING.
THIS WILL BRING THE NWLY SFC FLOW INTO SOUTH TEXAS MUCH
EARLIER...ROUGHLY AROUND NOON FRIDAY. CANADIAN MODEL IS MORE IN
LINE WITH THE ECMWF SOLUTION...SO HAVE GONE WITH THE EARLIER
FRONTAL PASSAGE ON FRIDAY. DRIER AIR WILL ARRIVE FRIDAY
EVENING...WITH A DRIER DAY WITH HIGHS IN THE MID 60S. SIGNIFICANT
DIFFERENCES IN LONG RANGE MODELS AS WELL WITH THE NEXT H5 TROUGH
DIVING ACROSS THE WESTERN US...WITH GFS DRIVING THE TROUGH THROUGH
TEXAS MONDAY NIGHT...WHILE THE ECMWF HOLDS THE TROUGH BACK INTO
THE MIDDLE OF NEXT WEEK. WITH THE SLOWER PROGRESSION OF THE LARGER
TROUGH RECENTLY...WILL LEAN MORE TOWARD THE ECMWF FOR THE LATE
TERM FORECAST.

MARINE...
NOW THROUGH TUESDAY...LIGHT TO MODERATE SOUTHEAST WINDS WILL
PREVAIL TODAY AND THIS EVENING AND SEAS WILL FALL TO AROUND 3 FEET
THIS EVENING AS A COLD FRONT APPROACHES THE AREA. THE FRONT WILL
SLOWLY MOVE THROUGH THE COASTAL WATERS THIS EVENING AND OVERNIGHT
WITH WINDS BECOMING NORTHEASTERLY BY TUESDAY MORNING. WINDS WILL
INCREASE TUESDAY WITH SMALL CRAFT EXERCISE CAUTION LIKELY AND
SMALL CRAFT ADVISORIES POSSIBLE. SEAS WILL JUMP BACK UP TO NEAR 5
FEET TUESDAY AS WELL.

TUESDAY NIGHT THROUGH FRIDAY...NE WINDS WILL SHIFT BACK TO THE
SOUTHEAST ON WEDNESDAY AS THE FRONTAL BOUNDARY WEAKENS. SOUTHEAST
WINDS WEDNESDAY AND THURSDAY WILL RUN AROUND 15 KNOTS...PRODUCING
SEAS RIGHT AROUND 4 FEET. CURRENT FORECAST HAS THE NEXT FRONT
ARRIVING FRIDAY AFTERNOON...WITH NW WINDS RETURNING AT 15 TO 20
KNOTS.

&&

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

$$

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