Area Forecast Discussion
Issued by NWS Brownsville, TX

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000
FXUS64 KBRO 250545
AFDBRO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
1145 PM CST TUE FEB 24 2015

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

&&

.AVIATION...THE 00Z BRO SOUNDING MAINTAINS A PRETTY STRONG AND
SATURATED LOW LEVEL INVERSION THIS EVENING BELOW THE 850 MB LEVEL
EXTENDING ALMOST DOWN TO GROUND LEVEL. THE NAM FORECAST SOUNDINGS
MAINTAIN THIS INVERSION THROUGH THE OVERNIGHT AND EARLY MORNING
HOURS WHICH WILL KEEP THE IFR/LIFR CEILINGS IN PLACE FOR THE REST OF
THE NIGHT FOR ALL THREE RGV AIRPORTS. AS THE 500 MB TROUGH AXIS TO
OUR NORTHWEST CLEARS THE REGION AROUND MIDDAY TOMORROW EXPECT DRIER
AIR TO START FILTERING INTO THE ATMS OVER DEEP SOUTH TX AND THE LOW
LEVEL INVERSION TO FINALLY BREAK. SO WILL INCLUDE VFR CONDITIONS
DURING THE LAST HALF OF THE 06Z TAF ISSUANCE FOR ALL OF THE VALLEY
AIRPORTS.

&&

.PREV DISCUSSION... /ISSUED 803 PM CST TUE FEB 24 2015/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...THE 00Z BRO SOUNDING SHOWS A PRETTY STRONG AND
SATURATED LOW LEVEL INVERSION THIS EVENING. NAM FORECAST SOUNDINGS
MAINTAIN THIS INVERSION THROUGH THE NIGHT WHICH WILL KEEP THE
IFR/LIFR CEILINGS IN PLACE FOR THE REST OF THE NIGHT. AS THE 500
MB TROUGH AXIS TO OUR NORTHWEST CLEARS THE REGION AROUND MIDDAY
TOMORROW EXPECT DRIER AIR TO START ENTRAINING INTO THE ATMS OVER
DEEP SOUTH TX AND THE LOW LEVEL INVERSION TO FINALLY BREAK. SO
WILL INCLUDE VFR CONDITIONS DURING THE LAST QUARTER OF THE 00Z TAF
ISSUANCE.

PREV DISCUSSION... /ISSUED 304 PM CST TUE FEB 24 2015/

SHORT TERM /NOW THROUGH WEDNESDAY NIGHT/...

RELEVANT FEATURES... A LARGE AND BROAD 90 TO 120KT 250MB SPEED MAX
IS SITUATED TO OUR NORTH WITH MORE MODERATE 50 TO 70KT FLOW
OVERHEAD. WEAK RIDGING IS APPARENT IN THE UPPER FLOW OVER TX/AR
WHICH IS BEING REINFORCED BY THE ADVANCING SPEED MAX AND HELPING
STRENGTHEN HIGH PRESSURE OVER SOUTHEAST TEXAS WHICH FOR NOW IS
CONTIUING TO ADVECT COLDER AIR IN FROM CENTRAL TEXAS VIA NORTHERLY
WINDS. A THICK LAYER OF OVERCAST SITS OVER THE AREA AND HIGHS ARE
STRUGGLING TO REACH THE MID 40S. ANOTHER UPPER LOW IS MOVING QUICKLY
SOUTH OVER ARIZONA EMBEDDED IN BROADER TROUGHING WHICH IS FORCING
SURFACE PRESSURE FALLS IN THE LEE OF THE SIERRA MADRE MOUNTAINS.

TONIGHT...
THE SOUTHEAST TEXAS RIDGE AXIS IS EXPECTED TO EXPAND SOUTHWESTWARD
TONIGHT WHICH WILL LEAD TO LIGHTER WIND SPEEDS THROUGH THE LATE
AFTERNOON AND EVENING. AS THE HIGH MOVES OFFSHORE THE UPPER LOW OVER
AZ WILL MOVE CLOSE ENOUGH TO BEGIN TO INFLUENCE OUR WEATHER ALLOWING
A LIGHT EASTERLY FLOW TO DEVELOP...ESPECIALLY OVER THE COASTAL
WATERS. THE POSITION OF 850/700MB TROUGHING WILL INCREASE WINDS OUT
OF THE SOUTH SOUTHWEST IN THAT LAYER. THE COMBINED FORCES SHOULD
INCREASE THE STRENGTH OF NEARSHORE COASTAL TROUGHING AND THERBY
SURFACE CONVERGENCE AND INDUCE A MODEST OVERRUNNING EFFECT
OVERNIGHT. THIS SHOULD INCREASE PRECIP CHANCES THE CLOSER YOU GET TO
THE COAST AND HAVE REFLECTED THAT IN THE GRIDS. ADDITIONALLY...WITH
A ONE TO TWO DEGREE F DEWPOINT DEPRESSION AT GULF OBSERVING
PLATFORMS CURRENTLY THE BRIEF DECREASE IN WIND SPEEDS OVER 68 DEGREE
WATER SHOULD KEEP FOG IN PLACE OVER THE GULF. WITH EASTERLY WINDS
FORMING LATER TONIGHT ACROSS THE EXISTING SST GRADIENT AND HIGHER
DEWPOINT AIR ABOUT 75NM OFFSHORE CONDITIONS APPEAR FAVORABLE FOR
SUSTAINED MARINE FOG THROUGH THE OVERNIGHT TONIGHT. TEMPERATURES
SHOULD ONLY COOL A FEW DEGREES OVERNIGHT UNDER THICK CLOUD COVER BUT
IT WILL STILL BE VERY CHILLY WITH LITTLE WARMING OCCURING DURING THE
DAY TODAY.

WEDNESDAY... ANOTHER REINFORCING SHOT OF NORTHWESTERLY AIR SHOULD
ARRIVE BY THE EARLY MORNING HOURS. INITIALLY THIS WILL RESULT IN
MORE COLD ADVECTION AND COUPLED WITH MORNING TEMPERATURES AROUND 30
WE WILL LIKELY BE VERY CLOSE TO WIND CHILL ADVISORY CRITERIA/30
DEGREES RGV...25 DEGREES RANCHLANDS/ BUT WILL LET THE EVENING SHIFT
TAKE A LOOK AT THIS BEFORE COMMITTING AS WIND CHILLS ARE FORECAST
RIGHT NOW TO BE ABOUT 30 TO 32 DEGREES. SHORT RANGE GUIDANCE ALSO
SHOWS A FAIRLY TIGHT TEMPERATURE GRADIENT THAT IS NUDGED WESTWARD BY
ADVANCING EASTERLIES. SOME GUIDANCE SHOWS THE LOWER VALEY AS WARM AS
50 DEGREES BY SUNRISE. HAVE DISCOUNTED THESE SOLUTIONS BUT IT
FURTHER LOWERS CONFIDENCE IN WIND CHILL ADVISORY LEVEL TEMPERATURES.
DRY NORTHWESTERLY WINDS AT THE SURFACE COUPLED WITH DRYING OF AN
ALREADY DRY LAYER ABOVE THE LOWEST 3000 TO 4000 FT OF ATMOSPHERE
SHOULD ALLOW THE SUN TO COME OUT IN FULL FORCE BY TOMORROW
AFTERNOON. THERE WILL STILL BE SOME RESIDUAL COLD ADVECTION WHICH
MAKES THE TEMPERATURE FORECAST CHALLENGING BUT WENT MID/UPPER 60S
INLAND...WHERE THE SUN WILL LIKELY COME OUT EARLIER AND UPPER
50S/LOW 60S COASTAL WHERE I BET THE COASTAL TROUGHING AND CLOUD
COVER WILL HOLD ON LONGER THAN ADVERTISED BY GUIDANCE KEEPING THAT
AREA COOLER.

WEDNESDAY NIGHT... NORTHWEST WINDS WILL WEAKEN AND SHIFT MORE
NORTHEASTERLY THROUGH THE NIGHT TUESDAY. SURFACE DEWPOINTS SHOULD BE
HIGH ENOUGH TO KEEP ESPECIALLY COLD TEMPERATURES AT BAY...BUT
REASONABLY CLEAR SKIES SHOULD COUPLE WITH EASING WIND SPEEDS TO
PRODUCE ANOTHER VERY CHILLY NIGHT. MIN TEMPS AVERAGE AROUND 41
DEGREES ACROSS THE AREA. /68-JGG/

LONG TERM...THURSDAY THROUGH TUESDAY/...EARLY IN THE LONG TERM PERIOD
A LONG WAVE TROUGH DEVELOPS EXTENDING FROM BAJA CA TOWARDS THE
NORTHEAST PLAINS WHILE AN AREA OF DRY AIR IS OVER NORTHERN MEXICO
AND SOUTH CENTRAL PORTION OF TEXAS. THE ABUNDANT SUNSHINE EXPECTED
WITH THIS DRY AIR WILL KEEP DRY CONDITIONS ACROSS THE AREA
THURSDAY WITH AN EASTERLY FLOW. LATE THURSDAY NIGHT INTO FRIDAY
THE SHOT OF COLD AIR FROM THE NEXT COLD FRONT ARRIVES AND FILTERS
INTO THE AREA WITH NE FLOW INCREASING WITH GUSTY WINDS. ANOTHER
OVERRUNNING SCENARIO DEVELOPS AS THE COASTAL TROUGH FORMS FRIDAY
AND THE SHEAR AXIS MOVES ACROSS TEXAS. SOUTHERLY 850MB WINDS
STRENGTHEN AND MOISTURE DEEPENS AS THE COLDER AIR BECOME DAMNED UP
AGAINST THE SIERRA MADRE. RAIN CHANCES INCREASE AS THE ISENTROPIC
LIFT STRENGTHENS IN RESPONSE TO THE DEVELOPING WESTERN TROUGH. THE
CHANCE OF RAIN INCREASE RIGHT ALONG THE COAST AND OVER THE
OFFSHORE WATERS. AS COLD AIR FILTERS INTO THE AREA THE TEMPS WILL
BEGIN TO LOWER INTO THE 40S OVERNIGHT. HIGH PRESSURE WILL SHIFT
EAST QUICKLY BRINGING BACK THE EAST TO SOUTHEAST FLOW THIS
WEEKEND. HIGHS WILL WARM UP INTO THE 60S AND 70S ACROSS THE CWA
SATURDAY AND SUNDAY.

INTO NEXT WEEK...ANOTHER UPPER LOW DEVELOPS OVER THE PACIFIC NORTHWEST
INCREASING THE SOUTHWESTERLY FLOW ACROSS SOUTH TEXAS. THE PRESSURE GRADIENT
WILL STRENGTHEN ACROSS THE SOUTH TX INDUCING STRONG SOUTHEAST FLOW
WITH GUSTY WINDS SUNDAY. CHANCE OF RAIN WILL BE LOW AS THE DEEPER
MOISTURE REMAINS TO THE NORTHEAST BUT THE CLOUD COVER WILL BE ON
THE INCREASE. A FEW ISOLATED SHOWERS WILL BE POSSIBLE ESPECIALLY
OVER THE COASTAL AREAS LATE IN THE LONG TERM PERIOD.

MARINE...NOW THROUGH WEDNESDAY NIGHT... NORTHWEST WIND SPEEDS WILL
DECREASE AND SLOWLY SHIFT THROUGH THE EAST AMID AREAS OF FOG THROUGH
THE NIGHT TONIGHT. STRONG NORTHWEST WINDS WILL BRING AN END TO THE
FOG BUT PRODUCE SMALL CRAFT ADVISORY CONDITIONS WITH SEAS BECOMING
ROUGH THROUGH THE REST OF THE DAY WEDNESDAY. IMPROVING CONDITIONS
ARE FORECAST THROUGH WEDNESDAY NIGHT.

THURSDAY THROUGH TUESDAY...SEAS WILL BEGIN TO BUILD IN RESPONSE TO THE
NORTHEAST FLOW INCREASING BEHIND A COLD FRONT EXPECTED LATE
THURSDAY INTO FRIDAY. THE POTENTIAL FOR SCA IS POSSIBLE
ESPECIALLY FROM THURSDAY EVENING THROUGH SUNDAY. THE HIGH PRESSURE
WILL BEGIN TO SHIFT EAST VEERING WINDS TO THE SOUTHEAST. DRY AIR
AND LIGHTER WINDS WILL RETURN FOR A SHORT PERIOD SUNDAY BUT
CONDITIONS DETERIORATE INTO MONDAY AS THE GRADIENT STRENGTHENS
ONCE AGAIN. WINDS WILL REMAIN BREEZE THROUGH TUESDAY AS ANOTHER
SYSTEM DEVELOPS OVER THE DESERT SOUTHWEST.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT ADVISORY FROM 4 AM TO 6 PM CST WEDNESDAY FOR GMZ130-
     132-135-150-155-170-175.

     DENSE FOG ADVISORY UNTIL 3 AM CST WEDNESDAY FOR GMZ150-155-170-
     175.

&&

$$

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HTTP://WEATHER.GOV/RGV

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