Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 221129
AFDBRO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
529 AM CST MON DEC 22 2014

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

&&

.AVIATION...AREAS OF FOG AND LOW CEILINGS WILL CONTINUE FOR
ANOTHER FEW HOURS THIS MORNING WIHT LIFR/IFR CONDITIONS
PREVAILING. SOUTHWESTERLY WINDS WILL DEVELOP IN THE LATE MORNING
AND HELP MOVE DRIER AIR INTO THE REGION OPENING SKIES UP TO VFR
CONDITIONS BY LATE MORNING. WINDS ARE EXPECTED TO BECOME VERY
LIGHT TONIGHT AND AREAS OF FOG AND LOW CLOUDS ARE LIKELY. IFR
CIG/VISBY OR WORSE IS ANTICIPATED BY AROUND MIDNIGHT LASTING THROUGH
EARLY MORNING. /68-JGG/

&&

.PREV DISCUSSION... /ISSUED 428 AM CST MON DEC 22 2014/

SHORT TERM...
KEY IMPACTS...
PATCHY MORNING FOG...VERY WINDY TUESDAY AFTERNOON.

RELEVANT FEATURES...
LARGE BROAD TROUGH OVER THE CENTRAL UNITED STATES WITH A LEADING
SUBTROPICAL JETMAX TO THE EAST AND SOUTHEAST AND AN ADVANCING JET MAX
TO THE WEST WITH PEAK INTENSITY STARTING TO APPROACH THE PACIFIC
NORTHWEST. SLOW MOVING TROUGHING AN A FRONT IS PUSHING INTO THE
WESTERN PLAINS...THE BEGINNINGS OF WHAT WILL MOVE THROUGH HERE ON
TUESDAY. VERY LIGHT WINDS PERSIST OVER THE AREA LOCALLY AND AREAS OF
FOG AND LOW CLOUDS ARE EXPECTED TO CONTINUE THROUGH HE NIGHT.

TODAY...
WINDS WILL SHIFT TO THE SOUTHWEST MOST OF THE DAY TODAY WHICH WILL
HELP USHER IN MUCH DRIER AIR AT THE SURFACE AND ALOFT. THIS WILL
RESULT IN A MOSTLY SUNNY DAY WITH TEMPERATURES WARMING INTO THE
UPPER 70S TO LOW 80S.

TONIGHT...
IMPACT...AREAS OF FOG.
THE PACIFIC NORTHWEST SPEEDMAX WILL SEND THE LARGE TROUGH OVER THE
CENTRAL US EASTWARD DURING THE OVERNIGHT. THE COLD FRONT OVER THE
PANHANDLES REGION WILL THEN START MOVING SOUTHEAST TOWARDS THE AREA.
PRESSURE GRADIENT WILL DECREASE OVER THE AREA SLACKENING WINDS AND
WITH MOISTURE POOLED AHEAD OF THE FRONT FOG WILL BE POSSIBLE.
CONTINUED THAT MENTION IN THE FORECAST AS INHERITED.

TUESDAY...
IMPACT...FRONT PRODUCING ESPECIALLY STRONG WINDS.
THROUGH TUESDAY MORNING THE STRONG PACIFIC NORTHWEST JET MAXIMUM
WILL HAVE SHIFTED THE UPPER TROUGH WELL TO THE EAST SENDING A DEEP
AND STRONG FRONT SOUTHEASTWARD THROUGH THE AREA. THE FRONT WILL HAVE
A VERY SHARP SLOPE DRYING THE ATMOSPHERE THROUGH ABOUT 500MB WITH
850/925MB WINDS INCREASING TO 40 TO 45 KTS. TEMPERATURE CHANGE WILL
BE A LITTLE BIT MEASURED DESPITE THE STRENGTH OF THE FRONT WITH THE
SOURCE AIRMASS FOR THIS SYSTEM LOCATED IN EASTERN NEW MEXICO AND
NORTHWEST TEXAS. DIVERGENCE ON THE LEFT EXIT REGION OF A SUBTROPICAL
JET MAXIMUM FORMING AS THE MAIN TROUGH MOVES EASTWARD IS ALSO
EXPECTED TO LEAD TO SURFACE CYCLOGENESIS IN THE NORTHWESTERN GULF OF
MEXICO FURTHER LOWERING INITIAL PRESSURES ALONG THE FRONTS PRESSURE
TROUGH. THE FRONT WILL LIKELY MOVE THROUGH BY LUNCHTIME ON TUESDAY.
WITH THE VERY AMPLIFIED PATTERN IN PLACE STRONG DIVERGENCE OVER THE
MIDDLE PLAINS WILL INCREASE SURFACE HIGH PRESSURE THERE...CREATING
AN EVEN STRONGER LOW LEVEL PRESSURE GRADIENT. NAM/GFS/ECMWF AVERAGES
SHOW ABOUT 1002 MB ACROSS THE LOWER VALLEY AT AROUND NOON TO 3PM
TUESDAY...INCREASING TO AROUND 1022MB BY 7AM TUESDAY MORNING. THAT
IS AN ESPECIALLY TIGHT GRADIENT AND WILL LIKELY LEAD TO AT LEAST A
PERIOD OF WIND ADVISORY LEVEL WINDS ACROSS MOST OF THE RIO GRANDE
VALLEY AND DEEP SOUTH TEXAS TUESDAY AFTERNOON AND AT LEAST PART OF
THE NIGHT TUESDAY NIGHT. WIND GUSTS OF 45 TO UP TO 50 MPH WILL BE
POSSIBLE. WINDS WILL LIKELY BE STRONG ENOUGH TO WREAK HAVOC ON
LARGER OUTDOOR DECORATIONS AND LAWN OBJECTS AND MAY DO MINOR DAMAGE
TO AWNINGS AND OTHER LESSER CONSTRUCTED BUILDING MATERIALS. DESPITE
THE SOMEWHAT COOL WATERS THE PRESSURE GRADIENT APPEARS STRONG ENOUGH
TO PRODUCE FREQUENT GALE FORCE GUSTS ON ALL WATERS...AND THE NAM/GFS
BRING SUSTAINED WINDS TO NEAR GALE FORCE ON THE OFFSHORE WATERS
TUESDAY NIGHT AND HAVE ISSUED A GALE WATCH WITH THIS FORECAST
PACKAGE. A BRIEF WINDOW FOR SHOWERS IS POSSIBLE RIGHT ALONG THE
FRONT BUT THE QUICK DRYING BEHIND THE FRONT WILL LIKELY PREVENT MUCH
IN THE WAY OF SIGNIFICANT/MEASURABLE RAINFALL. /68-JGG/

LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...A VERY SHARP 500 MB
TROUGH AXIS WILL DIG ACROSS THE CENTRAL PORTION OF THE COUNTRY ON
TUES AND WED WHICH WILL ALLOW A VERY DRY AND COOL AIRMASS TO
PREVAIL OVER DEEP SOUTH TEXAS AT MIDWEEK. THIS TROUGH WILL BE
FOLLOWED PRETTY QUICKLY BY A SECOND 500 MB TROUGH AXIS MOVING
OVER THE REGION ON SUNDAY. THE FIRST OF THESE 500 MB TROUGH
PASSAGES WILL BE FOLLOWED BY DECENT COOLER AIRMASS BUT BECAUSE OF
THE PROGRESSIVE NATURE OF THE 500 MB PATTERN THE WAA WILL RETURN
AGAIN ON THURS. THE CAA ASSOCIATED WITH THE SECOND 500 MB TROUGH
AXIS THIS SUNDAY WILL NOT BE AS STRONG AS THE FIRST WHICH WILL
RESULT IN A LITTLE MORE SUBTLE DROP IN TEMPS TOWARDS THE END OF THE
FORECAST PERIOD.

MOISTURE ADVECTION AHEAD OF THESE TROUGH AXES WILL REMAIN PRETTY
MINIMAL WITH THE BEST POPS ONLY REACHING SLGT CHC CATEGORY NEXT
WEEKEND WITH THE APPROACH OF THE SECOND 500 MB TROUGH.

LONGER RANGE ECMWF AND GFS GUIDANCE ARE IN PRETTY GOOD AGREEMENT
THROUGH AROUND FRI FOR THE OVERALL 500 MB POSITIONS WITH THESE
FIELDS SHOWING MORE DISAGREEMENT FOR SAT AND SUN. WILL LEAN CLOSER
TO THE ECMWF GUIDANCE THROUGH DAY 7. OVERALL CONFIDENCE IS A
LITTLE ABOVE AVERAGE AT THIS TIME DUE TO THE MODEL DISAGREEMENTS.

MARINE...
NOW THROUGH TUESDAY...
LIGHT WINDS AND LOW SEAS ARE FORECAST THROUGH MONDAY NIGHT ALTHOUGH
AREAS OF FOG MAY DEVELOP EARLY TUESDAY MORNING. A PARTICULARLY
STRONG COLD FRONT IS EXPECTED TO SWEEP ACROSS THE LOWER TEXAS COAST
DURING THE DAY TUESDAY BRINGING VERY STRONG WINDS AND RAPIDLY
ROUGHENING SEAS. WIND SPEEDS WILL INCREASE QUICKLY PRODUCING
FREQUENT GALE FORCE GUSTS ON THE LAGUNA MADRE AND NEARSHORE WATERS
AND SUSTAINED WINDS NEAR GALE FORCE ON THE OFFSHORE WATERS. AN
OCCASIONAL GUST APPROACHING STORM FORCE CANNOT BE COMPLETELY RULED
OUT WITH THIS SYSTEM. SEAS WILL CLIMB OVER TEN FEET BY TUESDAY
AFTERNOON. FORECAST WINDS ARE STRONGER THAN THE NORMAL STRONG
FRONTAL PASSAGE IN THIS REGION AND A GALE WATCH HAS BEEN ISSUED.
MARINERS ARE URGED TO MONITOR THE LATEST FORECASTS AND FACTOR THIS
POTENTIALLY DANGEROUS SYSTEM INTO YOUR PLANS.

TUESDAY NIGHT THROUGH FRIDAY...THE VERY STRONG POST FRONTAL PGF
WILL PREVAIL OVER THE LOWER TX GULF WATERS WELL INTO WED LIKELY
REQUIRING SCAS THROUGH MIDWEEK. THE PGF WILL RELAX FOR JUST A BIT
ON WED NIGHT BEFORE SWINGING AROUND BACK FROM THE S-SE ON THURS
AND FRI POSSIBLY PUSHING THE MARINE CONDITIONS BACK UP CLOSE TO
SCA LEVELS THROUGH FRI.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...GALE WATCH FROM TUESDAY MORNING THROUGH LATE TUESDAY NIGHT FOR
     GMZ130-132-135-150-155-170-175.

&&

$$

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