569  
FXUS64 KBRO 131129 AAA  
AFDBRO  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE BROWNSVILLE TX  
529 AM CST WED DEC 13 2017  
   
DISCUSSION
 
UPDATED FOR LATEST AVIATION DISCUSSION BELOW.  

 
   
AVIATION
 
GENERALLY BACKING WINDS WILL OCCUR DURING THE TAF  
PERIOD AS SURFACE HIGH PRESSURE MOVES OFF TOWARDS THE EAST. AS THE  
MID-LEVEL FLOW OVERHEAD BECOMES MORE PROMINENT OUT OF THE WEST-  
SOUTHWEST, HIGH CLOUDINESS WILL INCREASE.  

 
   
PREV DISCUSSION
 
/ISSUED 351 AM CST WED DEC 13 2017/  
 
SHORT TERM (NOW THROUGH THURSDAY): WEAK 500 MB RIDGING OVER THE BRO  
CWFA WILL QUICKLY FADE DURING THE PERIOD AND WILL BE REPLACED BY A  
WEST-SOUTHWEST TO EAST-NORTHEAST MID-LEVEL FLOW OVERHEAD AS FILLING  
500 MB LOW PRESSURE DROPS INTO THE BAJA PENINSULA. THIS PATTERN WILL  
RESULT IN RAPIDLY INCREASING CLOUDINESS, WITH NO RAIN TO BE FOUND  
UNTIL THURSDAY AFTERNOON AS A COLD FRONT EASES INTO DEEP SOUTH TEXAS  
AND THE RIO GRANDE VALLEY. DESPITE THE INCREASED CLOUD COVER,  
TEMPERATURES WILL MODERATE TO NEAR TO ABOVE NORMAL LEVELS AS AN  
ONSHORE FLOW REDEVELOPS AND INTENSIFIES AHEAD OF THE COLD FRONT.  
 
LONG TERM (THURSDAY NIGHT THROUGH TUESDAY): 00Z RUNS OF GFS AND  
ECMWF MODELS CONTINUE THEIR TREND OF CONVERGING SOLUTIONS, AS  
FIRST NOTED IN YESTERDAY AFTERNOON'S AFD. IN FACT, THEY NOW AGREE  
RATHER WELL, AT LEAST THROUGH THE WEEKEND.  
 
THE MOST ACTIVE WEATHER IS EXPECTED TO OCCUR DURING THE FIRST 36  
HOURS OR SO OF THE LONG-TERM PERIOD. LONG-LIVED CUTOFF LOW,  
APPARENT IN WV IMAGERY SPINNING OVER THE NORTHERN SEA OF CORTEZ  
CURRENTLY, WILL BE "RE-ENERGIZED" AS ANOTHER SHORTWAVE DROPS INTO  
IT ON THURSDAY NIGHT. MID-LEVEL SUBTROPICAL MOISTURE TAP AHEAD OF  
THIS FEATURE WILL BE MAINTAINED. MEANWHILE, AT THE SURFACE, A COLD  
FRONT WILL PROGRESSING SOUTHWARD THROUGH DEEP SOUTH TEXAS THURSDAY  
EVENING, SETTING THE STAGE FOR ISENTROPIC LIFTING. THE REGION WILL  
ALSO BE IN THE RIGHT-ENTRANCE REGION OF A JET STREAK, PROVIDING  
ADDITIONAL LIFT. SO FRIDAY HAS THE MAKINGS OF A RATHER CHILLY,  
RAINY DAY. (NO, IT WON'T BE A REPEAT OF OUR SNOW EVENT FROM THE  
PREVIOUS FRIDAY.) DROPPED TEMPS AND UPPED POP'S A BIT MORE, IN  
LINE WITH LATEST GUIDANCE. WITH GFS/ECM IN MUCH BETTER AGREEMENT,  
DIDN'T SEE MUCH REASON TO FIGHT SUPERBLEND. ONE AREA WHERE THERE  
IS STILL SOME DISAGREEMENT IS WHERE THE AXIS OF HEAVIEST PRECIP  
WILL FALL. OVERALL EVENT QPF TOTALS ARE GENERALLY IN THE 0.5-1.5"  
RANGE, BUT GFS (AND NAM) FAVOR THE SOUTHERN CWA, WHILE THE ECM  
PUTS MORE RAIN ACROSS THE NORTHERN TIER COUNTIES. TEMPS WILL  
SLOWLY FALL THROUGH THE DAY ON FRIDAY, DUE TO CLOUD COVER, RAIN,  
AND COLD-AIR ADVECTION, WITH AFTERNOON READINGS IN THE UPPER 40S  
TO NEAR 50F.  
 
PRECIP CHANCES/QPF TAPER OFF FRIDAY NIGHT INTO SATURDAY AS THE  
FRONT SAGS WELL SOUTH OF THE RIO GRANDE. THE OLD UPPER LOW  
FINALLY EJECTS QUICKLY TO THE NE, REACHING CENTRAL TX SATURDAY  
NIGHT. RAISED POP'S OVER THE NW COUNTIES SATURDAY EVENING AS SOME  
OF THE UPPER ENERGY MAY CLIP THIS AREA. LOOKED AT FORECAST  
SOUNDINGS FOR ANY THUNDER POTENTIAL, BUT ATMOSPHERE APPEARS TO  
REMAIN TOO STABLE. SATURDAY'S TEMPS WILL STILL STRUGGLE TO REACH  
60F, OR ABOUT 10 DEGREES BELOW NORMAL FOR MID-DECEMBER.  
 
A DRIER SW FLOW ALOFT KICKS IN SATURDAY NIGHT, PRETTY MUCH SHUTTING  
OFF MENTIONABLE PRECIP CHANCES. TEMPS ON SUNDAY AFTERNOON SHOULD  
WARM BACK NEAR NORMAL BEFORE ANOTHER, WEAKER COLD FRONT ARRIVES  
SUNDAY NIGHT. NOT EXPECTING MUCH IMPACT FROM THIS ONE, APART FROM  
PERHAPS SOME LIGHT COASTAL SHOWERS AND TEMPS ONCE AGAIN BEING  
KNOCKED DOWN TO A FEW DEGREES BELOW NORMAL. FOR TUESDAY AND  
WEDNESDAY, FAIRLY WEAK HIGH PRESSURE AT THE SURFACE AND QUASI-  
ZONAL FLOW ALOFT SHOULD ALLOW TEMPS TO REMAIN MODERATE (AT OR JUST  
ABOVE NORMAL) WITH NIL CHANCE FOR RAIN...THOUGH THERE ARE SOME  
MODEL DIFFERENCES IN THE PATTERN ALOFT TO BE IRONED OUT YET.  
 
MARINE (NOW THROUGH THURSDAY): BUOY 42019 REPORTED NORTH WINDS  
AROUND 10 KNOTS GUSTING TO AROUND 14 KNOTS WITH SEAS OF 3 FEET WITH  
A PERIOD OF 5 SECONDS AT 02 CST/08 UTC. THE CENTER OF SURFACE HIGH  
PRESSURE WILL MOVE EAST FROM TEXAS AND ACROSS THE GULF OF MEXICO,  
WITH A COLD FRONT EASING INTO THE LOWER TEXAS COASTAL WATERS AT THE  
END OF THE FORECAST PERIOD. LIGHT TO MODERATE WINDS AND LOW TO  
MODERATE SEAS WILL PREVAIL, WITH SMALL CRAFT EXERCISE CAUTION AND  
SMALL CRAFT ADVISORY NOT LIKELY TO BE NEEDED.  
 
THURSDAY NIGHT THROUGH MONDAY: A ROBUST COLD FRONT WILL MOVE  
SOUTHWARD THROUGH THE LOWER TEXAS COASTAL WATERS ON THURSDAY  
NIGHT, WITH STRONG NNE WINDS IN ITS WAKE. SMALL CRAFT ADVISORIES  
(SCA) ARE LIKELY TO BE IN EFFECT INTO FRIDAY NIGHT AS SEAS BUILD  
TO 8-9 FT. IN THE OFFSHORE GULF WATERS. RAINY CONDITIONS ARE ALSO  
EXPECTED DURING THIS PERIOD. WINDS AND SEAS IMPROVE, BECOMING  
MORE MODERATE FOR MUCH OF THE WEEKEND. A SECOND, WEAKER COLD FRONT  
IS PROGGED TO MOVE THROUGH THE WATERS SUNDAY NIGHT, WITH SMALL  
CRAFT EXERCISE CAUTION CONDITIONS LIKELY WITH SCA POSSIBLE FOR  
MONDAY.  

 
   
BRO WATCHES/WARNINGS/ADVISORIES
 
NONE.  

 
 

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