Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 021126 AAA
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
526 AM CST MON MAR 2 2015

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

&&

.AVIATION...LIFR CONDITIONS WILL PERSIST AREA WIDE FOR THE NEXT
SEVERAL HOURS BEFORE SLOWLY IMPROVING TO IFR BY LATE
MORNING/AFTERNOON WITH COASTAL TROUGHING PERSISTING ALONG THE
LOWER TEXAS COAST. NORTHEASTERLY WINDS ARE EXPECTED TO SHIFT
ONSHORE TONIGHT WITH THE INCREASE IN MOISTURE AND COOLING SURFACE
TEMPS EXPECTED TO CONTRIBUTE TO LOWERING CIGS. LIFR CONDITIONS ARE
FORECAST TO RETURN A FEW HOURS AFTER SUNSET. AREAS OF FOG WILL
LIKELY DEVELOP AS WELL. THERE IS A POSSIBILITY OF DENSE FOG BUT
CONFIDENCE IS TOO LOW FOR TAFS THIS PACKAGE. /68-JGG/

&&

.PREV DISCUSSION... /ISSUED 434 AM CST MON MAR 2 2015/

SHORT TERM /NOW THROUGH TUESDAY/...

RELEVANT FEATURES...
A BROAD UPPER LEVEL TROUGH IS SITUATED OVER THE
SOUTHWESTERN CONUS...JET MAXIMUM IS WORKING DOWN THE BACKSIDE OF
THAT TROUGH GIVING IT A KICK EAST TO SOUTHEASTWARD WHICH WILL HELP
GET OUR WEATHER PATTERN MOVING A BIT. MEANWHILE SHALLOW COLD AIR IS
PILED UP ACROSS MOST OF THE CENTRAL US DOWN THE FRONT RANGE OF THE
ROCKY MOUNTAINS AND SIERRA MADRES. BROADLY DIVERGENT SOUTHWESTERLY
UPPER AND MID LEVEL FLOW IS ALSO REINFORCING COASTAL TROUGHING JUST
OFF THE SOUTH TEXAS COAST.  AREAS OF FOG AND LOW CLOUDS PERSIST AND
IT WILL TAKE SOME PRETTY STRONG SYNOPTIC SCALE FORCING TO BREAK
EVERYTHING UP.

TODAY...
AS A RESULT EXPECT WE WILL PRETTY WELL STAY CLOUDY AND
DRIZZLY THROUGH THE DAY TODAY WITH MODERATE NORTH TO NORTHEASTERLY
WINDS. TEMPERATURES WONT WARM UP MUCH...MAYBE ABOUT 5 TO 7 DEGREES
FROM DAYTIME HIGHS. THE UPPER TROUGH GETS CLOSE ENOUGH BY LATE
AFTERNOON TO POSSIBLY SHIFT OUR WINDS TO THE EAST AND OUR 850MB
WINDS TO THE SOUTHWEST...BUT IT WILL LIKELY NOT BE IN TIME TO HAVE A
SIGNIFICANT IMPACT ON SENSIBLE WEATHER.

TONIGHT...
THE UPPER TROUGH POSITIONS ITSELF IN A WAY TO GENERATE BROADLY
DIVERGENT FLOW ALOFT THROUGH THE NIGHT WHICH INCREASES LEE SURFACE
TROUGHING. THIS LEADS TO MODERATE EASTERLY WINDS ALONG THE COAST AND
LIGHT WINDS INLAND. THIS WILL RESULT IN AT LEAST SOME MOISTURE
ADVECTION AND ANOTHER NIGHT OF PATCHY FOG LOOKS LIKELY WITH DENSE
FOG POSSIBLE. IT WOULD BE PRETTY MUCH ENTIRELY AN ADVECTION FOG
EVENT HOWEVER WITH THICK CLOUD COVER LIMITING RADIATIONAL COOLING.

TUESDAY... THE UPPER TROUGH BECOMES CLOSE ENOUGH TO INCREASE
SOUTHERLY WINDS AT THE SURFACE AND SOUTHWESTERLY WINDS JUST OFF THE
SURFACE WHICH SHOULD HELP BREAK UP LOW LEVEL CLOUDS AND ALLOW FOR A
BREEZY DAY WITH WARMER TEMPERATURES. GUIDANCE TRENDS OVER THE LAST
FEW DAYS SHOW STRONGER TROUGHING OVER THE NORTHWESTERN HALF OR SO OF
THE CWA AND THEY LIMIT THE STRONGEST WINDS TO THE IMMEDIATE COASTAL
LAND/SEA INTERFACE...WHICH WE SEE FREQUENTLY IN SUCH PATTERNS.
INHERITED FORECAST SHOWS THIS AND DIDNT ALTER MUCH.  850MB
SOUTHWESTERLIES DRY AND WARM THAT LAYER AND PUT A CAP ON ANY DEEP
CONVECTION DESPITE INCREASED LOW LAYER CONVERGENCE AND MOISTURE
ADVECTION. LOW CLOUDS MAY STICK AROUND LONGER ALONG THE IMMEDIATE
COAST AND CONTINUED HIGHS IN THE LOW TO MID 70S THERE WITH HIGHS
PUSHING THE MID 80S IN THE MID AND UPPER VALLEY. /68-JGG/

LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...A LARGE AND ELONGATED
500 MB TROUGH WILL DOMINATE THE ROCKIES ON TUES WITH THE TROUGH
AXIS PUSHING EAST INTO WED. THE NORTHERN SECTION OF THE TROUGH
AXIS WILL THEN SHEAR OFF OF THE SOUTHERN END OF THE TROUGH LATER
IN THE WORK WEEK WITH THE SOUTHERN END FORMING UP A CLOSED 500 MB
LOW OVER THE DESERT SW AND NW MEXICO AROUND FRI. ANOTHER FAST
MOVING SHORT WAVE WILL THEN DIVE SE FROM THE NW STATES WHICH WILL
OPEN UP THE CLOSED LOW AND PUSH IT EAST OVER TX THIS WEEKEND. THE
MAIN IMPACT FROM THIS PROGRESSION OF TROUGHS WILL BE A MAJOR
CANADIAN COLD FRONT PASSING THROUGH THE RGV LATE WED NIGHT/EARLY
THURS MORNING. THE POST FRONTAL COLD AIRMASS WILL REMAIN
ENTRENCHED OVER THE SOUTHEASTERN U.S THROUGHOUT MUCH OF THE
LATTER FORECAST PERIODS. MSL FIELDS ALSO INDICATE A STRONG
POTENTIAL FOR WEAK TO MODERATE SURFACE TROFFING PERSISTING ALONG
THE LOWER TX COASTLINE AFTER THE FROPA INTO THE WEEKEND. THE
PERSISTENT SURFACE COASTAL TROFFING WILL LIKELY MAINTAIN STEADY
MOISTURE CONVERGENCE OVER MUCH OF THE BRO CWA WHICH WILL LIKELY
MAINTAIN PLENTY OF LOW CLDS AND RAIN CHCS THROUGH DAY 7 AFTER THE
FRONT.

FREEZING TEMPS DO NOT APPEAR TO BE LIKELY AT THIS TIME IN THE WAKE
OF THE FRONT. HOWEVER SOME POINTS OF THE NORTHERN CWA COULD FLIRT
WITH NEAR FREEZING TEMPS THURS AND FRI MORNINGS.

THE ECMWF AND GFS ARE IN PRETTY GOOD AGREEMENT IN THE HANDLING OF
THE UPCOMING EVENT. AM WARY OF BOTH MODELS WANTING TO WARM UP
TEMPS SERIOUSLY IN THE WAKE OF THE FRONT AS BOTH OF THE LONGER
RANGE MODELS HAVE BEEN A LITTLE TOO QUICK IN WARMING UP TEMPS
AFTER A FROPA WHEN THE LOWER ATMS LAYERS REMAIN SATURATED FOR
EXTENDED PERIODS OF TIME. SO WILL UNDERCUT MODEL TEMPS A BIT IN
THE LONGER TERM MAINTAINING A COOLER BIAS. OVERALL POPS WILL BE A
GENERAL 50/50 BLEND OF THE ECMWF AND GFS. THE ECMWF HAS A DRIER
BIAS WITH THE GFS MEX MOS POPS MAINTAINING CHC POPS ALL THE WAY
THROUGH DAY 7.

MARINE...
NOW THROUGH TUESDAY... COASTAL TROUGHING WILL PERSIST
THROUGH MOST OF THE DAY TODAY WITH MODERATE NORTHERLY WINDS AND
MODERATE SEAS CONTINUING THROUGH THE DAY. AREAS OF DENSE FOG WILL
CONTINUE TO BE POSSIBLE THROUGH THE MORNING...ESPECIALLY CLOSE TO
PADRE ISLAND. AN INCREASE IN SOUTHERLY WINDS IS FORECAST TONIGHT
PERSISTING THROUGH TUESDAY WITH WIND SPEEDS LIKELY APPROACHING OR
EXCEEDING EXERCISE CAUTION LEVELS AMID MODERATE SEAS.

TUESDAY NIGHT THROUGH FRIDAY...THE MARINE CONDITIONS WILL DEGRADE
VERY QUICKLY LATE WED/EARLY THURS AFTER THE FROPA. CONDITIONS WILL
BE SOLIDLY SCA BORDERING ON GALE CONDITIONS FOR BOTH THE BAY AND
GULF WATERS INTO THURS/THURS NIGHT. THE MARINE CONDITIONS WILL
IMPROVE A LITTLE ON FRI AS THE PGF WEAKENS A BIT. HOWEVER SCAS
WILL LIKELY BE NEEDED FOR THE LOWER TX GULF WATERS INTO FRI.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...DENSE FOG ADVISORY UNTIL 8 AM CST THIS MORNING FOR TXZ251-256-
     257.

GM...DENSE FOG ADVISORY UNTIL 8 AM CST THIS MORNING FOR GMZ130-132-
     135-150-155.

&&

$$

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