Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 150129 AAA
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
829 PM CDT TUE APR 14 2015

.DISCUSSION...MSAS CAPE ANALYSIS SHOWS THAT VALUES OVER THE AREA
HAVE DROPPED BELOW THE 600 J/KG MARK AS A MORE STABLE NORTHERLY
SURFACE FLOW SPREADS OVER THE REGION. SO BELIEVE THAT THE CONV
THREAT WILL BE LOW THROUGH THE REST OF THE NIGHT DUE TO THE PRETTY
STABLE ENVIRONMENT IN PLACE. SO HAVE ALLOWED THE FFA TO EXPIRE.

&&

.AVIATION...IR SATL AND SURFACE OBS SHOWS PLENTY OF LOW AND MID
LEVEL CLD COVER IN PLACE OVER THE REGION. THE 00Z BRO SOUNDING
SHOWS TWO PRETTY SATURATED DECKS OVER THE RGV WITH THE TOP LAYER
LOCATED BETWEEN 650 AND 750 MB AND THE LOWER DECK LOCATED BETWEEN
875 AND 950 MB. EXPECT THE RESIDUAL MOISTURE TO LINGER THROUGHOUT
THE NIGHT ALLOWING FOR THE BETTER POTENTIAL FOR LOWER CEILINGS
LATER TONIGHT THROUGH SUNRISE WED. THE ATMS WILL THEN START TO
DESTABILIZE ON WED INCREASING THE CONV POTENTIAL DURING THE LATE
MORNING AND AFTERNOON HOURS. WILL INCLUDE A MENTION OF SOME PROB30
GROUPS FOR CONV LATE IN THE TAF PERIOD. THE WORST CEILINGS WILL
BE CONFINED TO THE OVERNIGHT AND EARLY MORNING HOURS WITH IFR
CONDITIONS POSSIBLE. DAYTIME HEATING AFTER SUNRISE TOMORROW WILL
THEN IMPROVE THE CEILINGS BACK UP TO MVFR/VFR LEVELS LATE IN THE
00Z TAF PERIOD.

&&

.PREV DISCUSSION... /ISSUED 347 PM CDT TUE APR 14 2015/

SHORT TERM.../NOW THROUGH WEDNESDAY NIGHT/...SATELLITE AND RADAR
IMAGES INDICATE THE CONVECTION ACROSS THE NORTHEAST MEXICAN COAST
CONTINUES TO MOVE EASTWARD THIS AFTERNOON WHILE CONVECTION CONTINUES
TO DEVELOP ACROSS EASTERN PORTIONS OF THE CWA EXTENDING OFFSHORE THE
LOWER TEXAS COAST ALONG THE WEAK COLD FRONT DRAPED ACROSS THE
NORTHERN COASTAL WATERS EXTENDING SOUTHWEST ACROSS THE MIDDLE AND
UPPER PORTIONS OF THE RIO GRANDE VALLEY. WITH THAT SAID...THE THREAT
FOR HEAVY RAINFALL APPEARS TO HAVE DIMINISHED ACROSS MOST OF THE CWA
AS THE STRONGEST SHOWERS AND THUNDERSTORMS ARE ALONG THE NORTHEAST
MEXICAN COAST. UNLESS CONVECTION REDEVELOPS ACROSS NORTHEAST MEXICO
AND MOVES INTO THE SOUTHERN PORTIONS OF THE CWA THIS EVENING...AS
PROGGED BY THE HRRR...THE THREAT FOR FLASH FLOODING APPEARS TO BE
OVER. WILL CONTINUE TO MENTION THE THREAT FOR HEAVY RAINFALL WITH
THUNDERSTORMS THIS EVENING EVEN AS RAIN CHANCES DIMINISH TONIGHT
WITH THE LOSS OF DIURNAL HEATING.

LOW TO MID LEVEL MOISTURE INCREASES ACROSS THE RIO GRANDE VALLEY AND
THE NORTHERN RANCHLANDS TONIGHT INTO WEDNESDAY AS THE WEAK COLD
FRONT STALLS AND WASHES OUT ACROSS THE AREA. ISOLATED TO SCATTERED
SHOWERS AND THUNDERSTORMS WILL DEVELOP ACROSS THE COASTAL SECTIONS
OF THE CWA WED MORNING AND RAIN CHANCES WILL INCREASE INLAND WED
AFTERNOON AS THE EASTERLY FLOW INCREASES ACROSS THE AREA AND DIURNAL
HEATING INCREASES. IN ADDITION...A WEAK 500MB SHORTWAVE TROUGH WILL
MOVE ACROSS THE STATE WEDNESDAY PROVIDING SOME UPPER LEVEL SUPPORT
FOR SHOWERS AND THUNDERSTORMS TO DEVELOP WED AFTERNOON INTO WED
EVENING.

LONG TERM.../THURSDAY THROUGH TUESDAY/...HIGHER THEN NORMAL
UNCERTAINTY RESIDES WITH THE LONG TERM FORECAST WITH MODEL
DIFFERENCES CONTINUING WITH THE 12Z MODEL PACKAGE.  MAIN PLAYER THAT
IS GIVING THE FORECAST HEADACHES IS AN EXPECTED CLOSED LOW/UPPER
TROUGH OVER THE ROCKIES AND SOUTHWEST U.S.

GFS REMAINS A SOMEWHAT OUTLIER AS IT CONTINUES TO BE THE FASTEST OF
THE 12Z MODEL SUITE IN THE UPPER LOWS EASTWARD MOVEMENT. 12Z GFS
IS LEANING TOWARDS A SLIGHTLY MORE OPEN PROGRESSIVE TROUGH WITH
THE EUROPEAN AND CANADIAN CLOSING THE TROUGH INTO A CLOSED LOW AND
DROPPING INTO THE 4 CORNERS VICINITY. A SLOWER MOVEMENT WILL
LIKELY KEEP THE REGION UNDER A MORE HIGHLY UNSETTLED WEATHER
PATTERN. ALL THE WHILE NORTH AMERICA REMAINS UNDER THE INFLUENCE
OF A SPLIT FLOW PATTERN WHICH WOULD CONTINUE AN ACTIVE SOUTHERN
SUBTROPICAL JET WHICH ADDS CONFIDENCE TO A CONTINUED ACTIVE WET
PATTERN THROUGH THE LONG TERM.

FORECAST WILL BE AN CONTINUATION OF A BLEND OF THE MODELS BUT FAVOR
SLIGHTLY WITH THE WETTER ECMWF UNTIL A MORE CLEAR CUT PATTERN
EVOLVES BEFORE TRENDING TO AN OVERALL LESSOR CHANCE OF RAIN.

RAIN CHANCES REMAIN HIGH ON THURSDAY WITH DIFFLUENT FLOW
INCREASING AS THE INFLUENCE OF THE UPPER TROUGH IS FELT. BOTH GFS
AND ECMWF SHOW AN MCS FEATURE DEVELOPING TO OUR NORTHWEST HAVING
THE POTENTIAL OF MOVING INTO THE CWA. FORECAST SOUNDINGS DO
INDICATE A HIGHLY UNSTABLE ATMOSPHERE AND A DECENT JET STRUCTURE
PASSING OVER SOUTH TEXAS WHICH COULD TREND INTO ANOTHER DAY OF
SEVERE WEATHER. SPC CURRENTLY HAS THE NORTHERN COUNTIES UNDER A
MARGINAL RISK BUT THIS COULD CHANGE OVER THE NEXT DAY OR TWO WITH
AN UPGRADE TO SLIGHT CHANCE FOR PORTIONS OR ALL THE CWA.

THE DIFFERENCES AND FORECAST UNCERTAINTY STARTS WITH A COLD FRONT
FRIDAY. THE FASTER GFS PUSHES A FRONT THROUGH THE AREA FRIDAY
NIGHT OR EARLY SATURDAY AND MOVES THE UPPER TROUGH TO THE
NORTHEAST OF TEXAS. A MUCH DRIER NORTHWEST FLOW DECREASES OR EVEN
ENDS THE RAIN CHANCES FOR THE WEEKEND. THE CANADIAN DOES NOT
MOVE THE TROUGH AXIS EAST UNTIL LATE SUNDAY WITH DRIER CONDITIONS
MONDAY AND TUESDAY. THE ECMWF KEEPS THE CHANCE OF RAIN INTO EARLY
NEXT WEEK WITH A MUCH SLOWER MOVEMENT OF THE FRONT NEVER REALLY
PUSHING THE FRONT THROUGH THE VALLEY KEEPING IT DRAPED ACROSS THE
THE REGION. THE ECMWF MAINTAINS A MORE CYCLONIC FLOW OVER TEXAS
INTO EARLY NEXT WEEK WITH THE GFS SHOWING MORE RIDGING. AND YET
ANOTHER UPPER TROUGH IS SEEN TO MOVE INTO NORTHWEST MEXICO BY
TUESDAY INITIATING ANOTHER INCREASE OF MOISTURE AND INCREASING
RAIN CHANCES MORE SO WITH THE WETTER ECMWF THEN THE DRIER GFS. THE
WETTER THAN NORMAL PATTERN WOULD LEAD THIS FORECASTER TO TREND IN
A HIGHER CHANCE FOR RAIN HOWEVER THE ECMWF HAS A WETTER BIAS IN
THE LONGER RANGE...THUS THE QUANDARY ON WHICH WAY TO TREND.
TEMPERATURE TRENDS ALSO TAKE ON A BLEND OF THE MODELS WHICH KEEP
TEMPERATURES RIGHT WHERE THEY HAVE BEEN FOR THE LAST SEVERAL DAYS
NEAR NORMAL HIGHS AND ABOVE NORMAL LOWS. WITH SOME EXCEPTION ON
THE MORE PROLIFIC RAIN DAYS.

MARINE /TONIGHT THROUGH WEDNESDAY NIGHT/...SEAS WERE NEAR 4 FEET
WITH EAST-NORTHEAST WINDS NEAR 10 KNOTS AT BUOY020 THIS AFTERNOON.
LIGHT NORTHEAST WINDS WILL PREVAIL ACROSS THE COASTAL WATERS
TONIGHT INTO WEDNESDAY AS A WEAK COLD FRONT DRAPED ACROSS THE
NORTHWEST GULF OF MEXICO STALLS AND WASHES OUT TONIGHT INTO
WEDNESDAY. LOW PRESSURE ACROSS WILL DEVELOP ACROSS NORTHWEST TEXAS
WEDNESDAY INTO WEDNESDAY NIGHT ALLOWING THE WINDS TO VEER TO THE
SOUTHEAST AND INCREASE WED NIGHT.

THURSDAY THROUGH SUNDAY...UNCERTAINTY ON A COLD FRONT PASSAGE
FRIDAY NIGHT/SATURDAY MORNING. GFS IS MORE AGGRESSIVE INDICATING
NORTHEAST WINDS AROUND 20 KNOTS WITH THE EUROPEAN MODEL KEEPING
THE FRONT NORTH OF THE COASTAL WATERS UNTIL SUNDAY ALBEIT IN A
MUCH WEAKENED STATE. A BLEND OF MODELS KEEPS A GENERAL MODERATE
ONSHORE FLOW THROUGH FRIDAY THEN WEAKENS THE FLOW OVER THE WEEKEND
WITH A RETURN OF SOUTHEAST WINDS EARLY NEXT WEEK. A LOW TO
MODERATE SEA IS EXPECTED TO PERSIST. MAIN CONCERN THROUGH THE
PERIOD IS THE CONTINUATION OF THUNDERSTORMS. BEST CHANCES ARE
THURSDAY AND FRIDAY WITH STILL A CHANCE OVER THE WEEKEND. ANY OF
THE STORMS WILL BE ABLE TO PRODUCE STRONG GUSTY WINDS, FREQUENT
LIGHTNING AND HIGHER SEAS.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  71  83  76  83 /  40  40  20  30
BROWNSVILLE          70  84  74  84 /  40  40  20  30
HARLINGEN            69  85  73  86 /  40  40  20  30
MCALLEN              72  86  73  87 /  40  40  20  30
RIO GRANDE CITY      69  86  73  88 /  30  30  20  20
SOUTH PADRE ISLAND   72  81  77  80 /  40  40  20  20

&&

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

$$

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

SHORT TERM...60
LONG TERM...67
GRAPHICAST/UPPER AIR...65


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