Area Forecast Discussion
Issued by NWS Brownsville, TX

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000
FXUS64 KBRO 211147 AAA
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
547 AM CST SUN DEC 21 2014

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

&&

.AVIATION...A MIX OF CONDITIONS AT THE TAF SITES THIS MORNING
WITH MFE EXPERIENCING IFR...HRL MVFR...AND BRO VFR UNDER CLOUDY
SKIES. LIGHT NORTH WINDS WILL VEER TO NORTHEAST TODAY...THEN EAST
AND SOUTHEAST TONIGHT. GUIDANCE SHOWS A RANGE OF SOLUTIONS...SO
CONFIDENCE IS MUDDY AS TO THE OUTCOME BUT PATCHY LIGHT FOG APPEARS
TO BE FAVORED AGAIN TONIGHT WITH THE LIGHT WINDS. CLOUDY SKIES ARE
ALSO FAVORED FOR ANOTHER DAY. THE GFS SEEMS TO BE VERIFYING BETTER
THAN THE NAM...WHICH HAS BEEN MUCH MORE PESSIMISTIC WITH ITS
OUTLOOK IN GENERAL. THE CONSENSUS SEEMS TO BE THAT MVFR CEILINGS
WILL PREVAIL...THOUGH FORECAST SOUNDINGS AND TIME HEIGHT ANALYSIS
SUGGEST THAT THE SATURATED LOW LEVEL LAYER WILL THIN OUT AND BE
ERODED BY DRIER AIR IN THE MID LEVELS.

&&

.PREV DISCUSSION... /ISSUED 329 AM CST SUN DEC 21 2014/

SHORT TERM /TODAY THROUGH MONDAY...THE SOUTHERN BRANCH OF THE NOAM
POLAR JET IS BRINGING UPPER MOISTURE OVER THE CWA FROM THE SOUTHWEST
THIS MORNING...WHILE A MID LEVEL TROUGH EXTENDING ALONG THE LEE OF
THE ROCKIES SHIFTS SLOWLY EAST. RIGHT REAR QUAD JET DYNAMICS WILL
SUPPORT MARINE SHOWER POTENTIAL THIS MORNING AS WILL THE DEVELOPMENT
OF WEAK COASTAL TROUGHING IN THE CONVERGENT NORTHEAST FLOW OVR THE
NORTHWEST GULF. THIS WILL AFFECT PRIMARILY THE LOWER VALLEY THIS
MORNING...WHICH WILL SEE LOW OVC SKIES AND A CHANCE OF LIGHT RAIN.
HIGH TEMPS TODAY WILL BE IN THE MID 60S...JUST A BIT BELOW NORMAL.

WINDS WILL VEER SLOWLY TO EAST AND THEN SOUTHEAST LATER TODAY AS
PLAINS LOW PRESSURE TAKES HOLD. CONCURRENTLY...JET DYNAMICS WILL
WEAKEN...LEAVING SUNDAY NIGHT WITH LIGHT SOUTHEAST TO SOUTH WINDS...
ABV AVG OVERNIGHT LOW TEMPS OF 55 TO 60 AND LIMITED RAIN CHANCES.
LIGHT WINDS AND MINIMAL DEW POINT DEPRESSION WILL SUPPORT PATCHY FOG
ACROSS THE AREA.

MONDAY WILL SEE A FEW BREAKS IN LOW CLOUD COVER BY AFTERNOON AS
SOUTH SOUTHEAST WINDS INCREASE TO MODERATE. HIGH TEMPERATURES WILL
BE SEVERAL DEGREES ABOVE NORMAL IN THE MID TO UPPER 70S. LITTLE
CHANGE IN THE SYNOPTIC SITUATION WITH LOWER PRESSURE UPSTREAM FROM A
CENTRAL PLAINS STORM SYSTEM RESULTING IN A MODERATE SOUTH WIND.
ANOTHER MID LEVEL TROUGH WILL MOVE SOUTHEAST FROM THE SOUTHERN HIGH
PLAINS INTO WEST TEXAS...AHEAD OF A BUILDING WEST COAST RIDGE AND
THE NEXT COLD FRONT SPILLING OUT OF THE PACIFIC NORTHWEST.

LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
A STRONG FRONTAL PASSAGE STILL LOOKS LIKELY ON TUESDAY. A STRONG
PACIFIC NORTHWEST JET MAXIMUM WILL HELP AMPLIFY AND SHARPEN BROAD
SLOW MOVING TROUGHING OVER THE CENTRAL US MONDAY NIGHT. AS THE UPPER
TROUGH SHARPENS IT FORMS A SURFACE LOW OVER THE GREAT LAKES REGION
AND SENDS A STRONG AND DEEP COLD FRONT ACROSS TEXAS. CONVERGENCE
BEHIND THE ADVANCING TROUGH STRENGTHENS SURFACE HIGH PRESSURE OVER
THE PLAINS FURTHER INCREASING THE PRESSURE GRADIENT BEHIND THE
FRONT.

ECMWF/NAM INCREASE SURFACE PRESSURES FROM AROUND 1003MB TUESDAY
MORNING TO ABOUT 1020MB WEDNESDAY MORNING. WHERE THE GFS PROGS THE
INITIAL PRESSURES TO BE A LITTLE LOWER DUE TO STRONGER SURFACE
TROUGHING AND GULF OF MEXICO CYCLOGENESIS NEARBY DUE TO INCREASED
DIVERGENCE RESULTING FROM THE INTERACTION OF THE SUBTROPICAL JET
WITH THE POLAR JET TROUGH. THE STRENGTH OF THAT LOW AT 1000-1002MB IS
LOWER THAN PREVIOUS RUNS AND THE 00Z GFS SHOWS SUSTAINED GALE FORCE
WINDS OVER THE OFFSHORE GULF WATERS...WHILE THE NAM AND ECMWF DO NOT
DEVELOP PRESSURES THIS LOW AND SHOW WIND SPEEDS OVER THE GULF CLOSER
TO 26 TO 32 KNOTS. THE GFS DOES ALSO DEVELOP 850MB WINDS AROUND
47KTS OVER LAND DURING THE AFTERNOON WHERE THE NAM/ECMWF KEEP THOSE
STRONGER WINDS AT BAY UNTIL NIGHT WHEN THE CORE OF HIGH PRESSURE
MOVES CLOSER TO THE AREA. THE SOURCE AIRMASS REGION IN SOUTHEASTERN
COLORADO AND NEW MEXICO IS NOT ESPECIALLY COLD...WHICH WILL LIMIT
COLD ADVECTION AND DOWNWARD MIXING OF THOSE STRONGER GUSTS OVER THE
WATER...TO A DEGREE...BUT GULF WATER TEMPERATURES OF 74 DEGREES
OFFSHORE AND 68 DEGREES NEARSHORE WILL SUPPORT SOME MIXING WITH A
PRESSURE GRADIENT THAT STRONG. THE VERY SHARP AND DEEP FRONTAL
GRADIENT LOOKS TO KEEP MUCH IN THE WAY OF PRECIPITATION AT BAY.

GIVEN THE UPPER JET PATTERN PRESENTED BY BOTH THE GFS/ECMWF PREFER
THE GFS SOLUTION IN TERMS OF WIND SPEED AND HAVE PARTICULARLY STRONG
WINDS IN THE NEW FORECAST...WHICH IS CLOSE TO THE PREVIOUS PACKAGE.
WIND GUSTS OF 40 TO 45 MPH OVER LAND AND WIDESPREAD GALE FORCE GUSTS
OVER ALL GULF WATERS WITH GUSTS OF 38 TO 43 KTS ARE INCLUDED.
BELIEVE THE FINAL DETERMINANT ON WHETHER WE EXPERIENCE A WIDESPREAD
WIND ADVISORY/GALE WARNING DAY WILL BE TIED TO THAT GULF
CYCLOGENESIS AND OUR INITIAL SFC PRESSURE. A 20MB INCREASE IN LESS THAN
24 HOURS WILL DO IT SO YOU MIGHT WANT TO HOLD ON TO YOUR DECORATIVE
SANTAS AND SNOWMEN! STAY TUNED.

EXPECTING CHILLY HIGHS IN THE MID 60S FOR WEDNESDAY WITH A
PERSISTENT NORTHWEST BREEZE BUT OVERALL NOT NEARLY AS WINDY. WINDS
WILL SHIFT BACK TO THE SOUTH ON CHRISTMAS DAY WITH TEMPERATURES
WARMING BACK INTO THE LOW 70S AMID RELATIVELY CLEAR SKIES WITH ALL
OF THE MOISTURE SWEPT AWAY BY THE FRONT. WINDS MAY GET A BIT BREEZY
DURING THE DAY BEFORE DECREASING IN ADVANCE OF THE NEXT COLD
FRONT...WHICH ARRIVES FRIDAY NIGHT. THIS FRONT IS MORE OF THE
SHALLOW COLD AIR VARIETY WHICH SHOULD PROMOTE A LITTLE MORE
OVERRUNNING...BUT AVAILABLE MOISTURE LOOKS PRETTY LIMITED AND KEPT
RAINFALL CHANCES PRETTY LOW. THE SOURCE AIRMASS REGION FOR THIS
FRONT...WHICH IS PARTIALLY HELPED BY COLD AIR DAMMING PROCESSES IS
IN WYOMING AND NORTHEASTERN COLORADO AND SHOULD RESULT IN COLDER AIR
FILTERING IN. HIGHS BY SUNDAY LOOK TO BE CLOSER TO 58 TO 62 DEGREES.
/68-JGG/

MARINE...
TODAY THROUGH MONDAY...THE APPROACH OF A MID LEVEL TROUGH FROM THE
WEST...COUPLED WITH THE RIGHT REAR QUADRANT OF A SOUTHERN BRANCH
POLAR JET STREAK OVER THE NORTHWEST GULF WILL KEEP SHOWER POTENTIAL
ALIVE TODAY. OTHERWISE...LIGHT NORTHEAST WINDS AND LOW TO MODERATE
SEAS RESULTING FROM A WEAK GRADIENT WILL CONTINUE. PRESSURE FALLS
OVER THE HIGH PLAINS WILL HELP REORIENT WINDS TO LIGHT SOUTH TONIGHT
AND MONDAY...INCREASING TO MODERATE SOUTHEAST BY MONDAY AFTERNOON
WHILE SEAS REMAIN LOW TO MODERATE.

MONDAY NIGHT THROUGH THURSDAY...
MODERATE SOUTHEAST WINDS ARE FORECAST AMID LOW SEAS MONDAY NIGHT.
TUESDAY MORNING A STRONG COLD FRONT WILL SWEEP ACROSS THE LOWER
TEXAS COAST. FREQUENT GALE FORCE GUSTS WILL BE POSSIBLE FOR ALL
WATERS WITH SEAS BECOMING VERY ROUGH. SIGNIFICANT WAVE HEIGHTS WILL
LIKELY PEAK AROUND 11 TO 13 FEET. WINDS WILL REMAIN STRONG THROUGH
THE DAY WEDNESDAY WITH SEAS OVER 8 FEET EXPECTED THROUGH WEDNESDAY
EVENING. WIND SPEEDS WILL DECREASE EARLY THURSDAY MORNING AND SHIFT
BACK TO THE SOUTH WITH SEAS BECOMING MORE MODERATE. MARINERS ARE
ADVISED TO CLOSELY MONITOR THE LATEST FORECASTS REGARDING THE
UPCOMING FRONTAL PASSAGE AND FACTOR ITS POTENTIAL HAZARDS INTO YOUR
PLANS.

&&

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

$$

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54/68/CAMPBELL




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