Area Forecast Discussion
Issued by NWS Brownsville, TX

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000
FXUS64 KBRO 230527 AAA
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
1227 AM CDT MON MAR 23 2015

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

&&

.AVIATION...VERY LIGHT EASTERLY WINDS ACROSS THE AREA COUPLED WITH
CLEAR SKIES AND LOW DEWPOINT DEPRESSIONS HAVE THE REGION PRIMED
FOR FOG. VISBYS AREA ALREADY FLUCTUATING AT A FEW SITES AND WILL
LIKELY DROP QUITE A BIT MORE THROUGH 08Z. FORECASTING PREVAILING
LIFR WITH SOME VLIFR CONDITIONS POSSIBLE THROUGH DAYBREAK. DRIER
AIR JUST OFF THE SURFACE SHOULD BEGIN TO MIX DOWN BY 8 TO 9 AM AND
LEAD TO RAPIDLY IMPROVING CONDITIONS WITH VFR SKIES FORECAST UNDER
MODERATE EAST WINDS THROUGH THE REST OF THE DAY ON MONDAY. VFR
CONDITIONS ARE FORECAST AGAIN THROUGH MONDAY EVENING WITH SLIGHTLY
HIGHER WIND SPEEDS BUT AT LEAST SOME FOG FORMATION WILL BE
POSSIBLE OVERNIGHT MONDAY INTO TUESDAY AS WELL. /68-JGG/

&&

.PREV DISCUSSION... /ISSUED 749 PM CDT SUN MAR 22 2015/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...THE MAIN FORECAST ISSUE FOR THE OVERNIGHT HOURS WILL
BE THE POTENTIAL FOR MORE FOG/LOW CLOUDS FOR THE RGV AIRPORTS.
THE 00Z BRO SOUNDING SHOWS A FAIRLY NARROW SATURATED LAYER BETWEEN
THE 975-950MB LEVELS. AS THE NIGHTTIME INVERSION REFORMS OVER THE
NEXT SEVERAL HOURS EXPECT THE LOWER CEILINGS/VSBYS TO REDEVELOP AS
LIGHT SURFACE WINDS WILL PERSIST ON FOR A FAIRLY LONG TIME PERIOD
TONIGHT THROUGH SUNRISE MONDAY. EXPECT IFR/LIFR CONDITIONS TO
PREVAIL LATER TONIGHT AS THE CEILINGS/VSBYS DEGRADE. AFTER SUNRISE
TOMORROW DAYTIME HEATING AND INCREASING LOW LEVEL MIXING WILL
QUICKLY ERODE AWAY ANY LOW CLDS/FOG THAT FORMS. THIS WILL ALLOW A
RETURN OF VFR CONDITIONS FROM AROUND EARLY TO MIDMORNING AND
CONTINUING INTO THE AFTERNOON HOURS. THE MAV/MET AND GFS LAMP
GUIDANCE ALL REFLECT A PRETTY STRONG FOG SIGNAL FOR TONIGHT DUE TO
THE LIGHT SURFACE WINDS AND ELEVATED LOW LEVEL DEWPOINTS. WILL GO
WITH A GENERAL BLEND OF THESE AS INPUT INTO THE 00Z TAF ISSUANCE.

PREV DISCUSSION... /ISSUED 247 PM CDT SUN MAR 22 2015/

.AT LONG LAST: SEVERAL DAYS OF SUNSHINE AND WARMTH...

SHORT TERM /NOW THROUGH MONDAY NIGHT/...ONE MIGHT SAY WE`VE EARNED
THIS. IN A MONTH WHERE RAINFALL RECORDS HAVE EITHER FALLEN (UPPER
VALLEY/RIO GRANDE PLAINS RANCHLANDS) OR RANKED IN THE TOP TEN...AND
TEMPERATURES HAVE BEEN SUPPRESSED IN GENERAL DUE TO THE CLOUDS AND
PRECIPITATION...SUNSHINE IS *FINALLY* ON ITS WAY.
UNFORTUNATELY...THAT`S LITTLE COMFORT FOR THE SPRING BREAKERS WHO
DEALT WITH DAY OF DAY OF FOG...INTERSPERSED WITH RAIN AND GENERALLY
COOL WEATHER WITH FEW EXCEPTIONS ON THE BEACH.

THE PASSAGE OF THE UPPER LEVEL LOW THAT GAVE TEXAS MORE MUCH
WELCOMED RAIN BUT PERHAPS TOO MUCH FOR AGRICULTURAL INTERESTS HERE
IN THE VALLEY WILL BE FOLLOWED BY FLAT UPPER RIDGING THROUGH THE
SHORT TERM...ENSURING NO PRECIPITATION AND PLENTY OF DAYTIME
SUNSHINE AND EVENING STARRY SKIES.

THE PRIMARY POTENTIAL HAZARD IS DENSE FOG AFTER MIDNIGHT THROUGH THE
MONDAY MORNING COMMUTE.  ALL FACTORS ALIGN PERFECTLY FOR DENSE
RADIATION FOG...WHEN THE GROUND/SURFACE TEMPERATURE FALLS TO THE
DEWPOINT /100 PERCENT HUMIDITY/ WHILE AIR JUST ABOVE THE GROUND ALSO
REACHES 100 PERCENT HUMIDITY AT SLIGHTLY HIGHER TEMPERATURES. CLEAR
SKIES...CALM WINDS...ABUNDANT SOIL MOISTURE FROM LAST WEEK`S
WIDESPREAD RAIN...AND STARTING DEWPOINTS CLOSE TO THE AIR
TEMPERATURE JUST A FEW HOURS AFTER SUNSET SET THE STAGE.  FOG
FORMING NEAR THE GROUND BEFORE MIDNIGHT WILL BECOME DENSE AND
THICKEN VERTICALLY...PROBABLY ONLY TO 200-500 FEET...WHICH IS PLENTY
HAZARDOUS FOR DRIVING...BOATING...AND LANDING AT AREA AIRPORTS.

DENSE FOG ADVISORIES WILL LIKELY BE REQUIRED FOR ALL OR PART OF THE
REGION LATER THIS EVENING...SO STAY TUNED FOR THAT.  OTHERWISE...THE
INITIAL CLEAR SKIES AND LIGHT/CALM WINDS WILL ALLOW TEMPERATURES TO
QUICKLY FALL INTO THE 60S...AND BOTTOM OUT IN THE UPPER 50S IN MOST
AREAS AFTER 4 AM MONDAY WHICH IS A DEGREE OR TWO BELOW MODEL
FORECASTS WHICH TYPICALLY FAIL TO HANDLE LOCAL RADIATIONAL COOLING
ACROSS DEEP SOUTH TEXAS.

THAT FOG WILL BURN OFF BY 10 AM MONDAY...LEAVING PRISTINE BLUE SKIES
AND FULL SUNSHINE. WE`VE SEEN FEW INSTANCES OF THIS RECENTLY...THE
LAST STRING WAS IN LATE FEBRUARY. THE ATMOSPHERE AND SUN ANGLE HAVE
CHANGED CONSIDERABLY AND TEMPERATURES WILL HAVE NO PROBLEM REACHING
INTO THE 80S JUST ABOUT EVERYWHERE...SAVE FOR THE BEACH WHERE
ONSHORE FLOW WILL KEEP VALUES FROM GETTING MUCH HIGHER THAN 75.

THE DRY AIR HOLDS FORTH MONDAY NIGHT INTO TUESDAY MORNING...SO
EXPECT MAINLY CLEAR SKIES WITH A LIGHT SOUTH TO SOUTHEAST WIND.
WITH MODEST DRYING MONDAY DON`T EXPECT THE DENSITY AND COVERAGE OF
DENSE FOG THAT WE`LL SEE TONIGHT...BUT PATCHY TO AREAS IS QUITE
LIKELY AS IT WILL TAKE MUCH MORE THAN ONE DAY TO DRY THINGS OUT IN
THE SUB-SURFACE SOIL LAYER.  TEMPERATURES JUST A TICK ABOVE THOSE ON
MONDAY MORNING.

LONG TERM /TUESDAY THROUGH SUNDAY/...THE FORECAST PERIOD BEGINS
WITH TRANQUIL CONDITIONS ACROSS DEEP SOUTH TEXAS AND THE RIO
GRANDE VALLEY COURTESY OF WEAK 500MB RIDGING AND ZONAL FLOW. WARM
AND DRY CONDITIONS WILL PREVAIL ACROSS THE AREA TUESDAY THROUGH
WEDNESDAY. LINGERING PATCHY FOG POSSIBLE THROUGH MID MORNING
TUESDAY...OTHERWISE...ABUNDANT SUNSHINE WITH SUBSIDENCE ALOFT
WILL ALLOW HIGH TEMPERATURES TO REACH THE LOW TO MID 80S...EXCEPT
FOR 70S NEAR THE COAST...TUESDAY AND WEDNESDAY. OVERNIGHT LOW
TEMPERATURES EACH NIGHT WILL BE GENERALLY IN THE 60S UNDER MOSTLY
CLEAR SKIES.

500MB RIDGE WILL BUILD ALONG THE WEST COAST BY MID WEEK...ALLOWING
SURFACE HIGH PRESSURE TO SPILL OUT OF THE PACIFIC NORTHWEST AND INTO
THE PLAINS WEDNESDAY INTO WEDNESDAY NIGHT. THIS WILL RESULT IN A
WEAK COLD FRONT MOVING INTO DEEP SOUTH TEXAS ON THURSDAY. MOISTURE
WILL MOISTURE POOL AHEAD OF THE APPROACHING FRONT AND WILL SUPPORT
SOME CONVECTION ACROSS DEEP SOUTH TEXAS WEDNESDAY NIGHT INTO
THURSDAY NIGHT. SLIGHTLY COOLER AIR ALOFT SHOULD SUPPORT LIMITED
INSTABILITY...SO WILL MENTION ISOLATED THUNDER FOR WEDNESDAY NIGHT AND
THURSDAY. PARTIAL CLEARING SKIES EXPECTED BY LATE FRIDAY WITH A
FEW SHOWERS LINGERING NEAR THE COAST...MAINLY IN THE MORNING.
DIFFERENCES DEVELOP BETWEEN THE GFS AND ECMWF TOWARDS THE LATTER
PORTION OF THE FORECAST. WILL LEAN TOWARDS THE DRIER GFS AND
PREVIOUS FORECAST...WITH COOLER AND DRIER CONDITIONS ACROSS THE
REGION THROUGH THE WEEKEND. HIGH TEMPERATURES GENERALLY IN THE
70S AND OVERNIGHT LOW TEMPERATURES IN THE 50S TO LOWER 60S.

MARINE /NOW THROUGH MONDAY NIGHT/...GOT FISHING PLANS?  AT LONG
LAST...SEA FOG RAIN OR NUISANCE ROUGH SEAS ARE NOT IN THE CARDS FOR
THE GULF. THE LAGUNA MAY DAWN FOGGY FOR ANY FISHING MONDAY SO
BOATERS MAY WANT TO DELAY TRIPS UNTIL MID MORNING WHEN CONDITIONS
IMPROVE RAPIDLY.

OTHERWISE...SLIGHT SEAS...2 FEET OR LESS...AND LIGHT WINDS...10
KNOTS OR LESS...DOMINATE THE SHORT TERM.  THICK DRY AIR OVER THE
GULF ENSURES NO SEA FOG ISSUES THROUGH AT LEAST TUESDAY MORNING.

TUESDAY THROUGH FRIDAY...LIGHT TO MODERATE SOUTHEAST WINDS AND LOW
TO MODERATE SEAS WILL PREVAIL THROUGH MIDWEEK. MODERATE TO STRONG
NORTHEAST WINDS WILL DEVELOP THURSDAY AFTERNOON AS A WEAK COLD FRONT
MOVES THROUGH THE AREA. SMALL CRAFT EXERCISE CAUTION LIKELY AND
SMALL ADVISORY CONDITIONS POSSIBLE THURSDAY INTO FRIDAY. SHOWERS AND
ISOLATED THUNDERSTORMS WILL DEVELOP ON THURSDAY WITH THE PASSAGE
OF A FRONT.

&&

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

$$

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