Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 182333 AAA
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
633 PM CDT SAT APR 18 2015

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

.AVIATION...A FEW SHOWERS HAVE ATTEMPTED TO GET GOING OVER THE
COASTAL COUNTIES OF DEEP SOUTH TEXAS...HOWEVER THEY HAVE LARGELY
FIZZLED OUT DUE TO A MORE STABLE ATMOSPHERE AIDED BY THE FRIDAY
EVENING/NIGHT CONVECTION. CURRENT SATELLITE IMAGERY DOESN/T SHOW
ANY CONVECTION IN THE VICINITY OF THE AERODROMES AND THIS HAS
BEEN REMOVED FROM THE PREVIOUS TAFS. SURFACE WINDS WILL LIKELY
REMAIN TOO STRONG OVERNIGHT TO ALLOW FOR SIGNIFICANT FORMATION OF
FOG...BUT A TEMPO HAS BEEN INCLUDED FOR LIGHT FOG DEVELOPMENT FOR
NEAR SUNRISE SUNDAY MORNING. PREVIOUSLY-LOWER CEILINGS HAVE BEEN
BEEN DUMPED IN FAVOR OF THE MID AND HIGH LEVEL CLOUDINESS
STREAMING OVERHEAD OUT OF NEIGHBORING MEXICO. OVERALL...VFR
SHOULD BE THE RULE THROUGH THE NEXT 24 HOURS.
&&

.PREV DISCUSSION... /ISSUED 255 PM CDT SAT APR 18 2015/

SHORT TERM.../NOW THROUGH SUNDAY NIGHT/...A LOW PRESSURE SYSTEM
CENTERED OVER EASTERN COLORADO IS MAINTAINING A BROAD AREA OF
DIFFLUENT FLOW ALOFT OVER SOUTH CENTRAL TEXAS. ALSO ...A VERY
ACTIVE SUB TROPICAL JET WITH SHORTWAVES WITHIN THE FLOW IS MOVING
ACROSS SOUTH TX UNDERNEATH THIS LOW. THIS WILL CONTINUE TO PRODUCE
NUMEROUS SHOWERS AND THUNDERSTORMS ALONG THE LOWER TEXAS GULF
WATERS NORTHEAST INTO THE NORTHWEST GULF COAST. THERE IS AN AREA
OF CONVECTION DEVELOPING ALONG A STATIONARY FRONT WHICH IS
INTERACTING WITH PLENTY OF DEEP LAYER MOISTURE AND INSTABILITY
POOLED ALONG IT. NEAR THE SURFACE DEW POINTS RANGE FROM 70 TO 75
DEGREES AND PRECIPITABLE WATER VALUES IN THE LAST KBRO 12Z
SOUNDING SHOWS 1.96 INCHES AND THE LATEST RAP MODEL RUN SHOWS
PWATS OF 1.5 TO 1.9 INCHES ESPECIALLY FROM HIDALGO COUNTY
NORTHEAST AND EAST TOWARDS THE COAST. IN ADDITION...THE A SLIGHT
BREAK IN THE CLOUDS IS ALLOWING FOR TEMPS TO WARM UP FOR THE NEXT
FEW HOURS RESULTING IN INCREASE INSTABILITY ACROSS THE AREA. THIS
WILL RESULT IN A CONTINUATION OF THE CONVECTION IN THE LATE
AFTERNOON THROUGH THE OVERNIGHT HOURS THROUGH MIDNIGHT. THE
CONVECTION WILL ALSO BE ENHANCE ALONG THE SIERRA MADRE AND MOVE
NORTHEAST WHICH WILL MAKE ITS WAY INTO STARR AND HIDALGO COUNTY
LATE EVENING INTO THE OVERNIGHT. THE MAIN THREAT WITH THESE STORMS
WILL BE VERY HEAVY DOWNPOURS PRODUCING FLOODING...STRONG DAMAGING
WINDS...HAIL AND FREQUENT CG LIGHTNING. INTO SUNDAY THE UPPER
LEVEL JET WILL MAKE ITS WAY INTO SOUTH TEXAS PROVIDING SUPPORT FOR
SOME CONVECTION TO DEVELOP SUNDAY AFTERNOON. EXPECT THE BEST
POTENTIAL TO REMAIN ALONG THE COAST DUE TO THE INSTABILITY IN THE
AREA. EXPECT A FEW OF THE STORMS TO BECOME SEVERE. THE CLOSED LOW
BECOMES AN OPEN WAVE AS IT MOVES NORTHEAST INTO THE GREAT LAKES
SUNDAY NIGHT PUSHING A COLD FRONT BEHIND IT ALONG THE CENTRAL
PLAINS. THE CONVECTION WILL BE ENHANCE EVEN MORE OVERNIGHT SUNDAY
ASSOCIATED TO THE BOUNDARY AS THE FRONT APPROACHES THE AREA. THE
FRONT WILL ARRIVED BY THE END OF THE SHORT TERM OVER THE NORTHERN
RANCHLANDS EARLY MONDAY MORNING.

LONG TERM.../MONDAY THROUGH SATURDAY/...THE CLOSED LOW THAT
HAS BEEN PLAUGING THE REGION WITH INTERMITTENT THUNDERSTORMS FOR
THE LAST SEVERAL DAYS OPENS UP AND MERGES WITH A SHARP SHORTWAVE
TROUGH UPPER TROUGH MOVING OUT OF CANADA. THE RESULT WILL BE A
LARGE SCALE UPPER TROUGH DEVELOPING MONDAY INTO TUESDAY FROM THE
NORTHERN PLAINS TO THE MIDWEST EXTENDING SOUTH INTO THE GULF
SOUTH. THIS SENDS A COLD FRONT THROUGH SOUTH TEXAS SUNDAY NIGHT
MOVING OFFSHORE THE LOWER TEXAS COAST AS EARLY AS SUNRISE MONDAY.
MODELS ARE IN GOOD AGREEMENT AND REMAIN VERY CONSISTENT WITH THE
EVOLUTION OF THE UPPER LEVEL AND SURFACE FEATURES. MODERATE TO
HIGH CONFIDENCE IN THE FORECAST THROUGH TUESDAY MAINTAINS A
LOWERING OF TEMPERATURES AND HIGHER CHANCES OF RAINFALL. THE
COOLING OF THE LOWER ATMOSPHERE, LOWER LAPSE RATES, WEAKENING
INSTABILITY WILL LIMIT THE THUNDERSTORM INTENSITY AND SEVERE
WEATHER PROBABILITIES GO WAY LOW. GFS MODEL SOUNDING CONTINUE TO
INDICATE THE BEST CHANCE OF THUNDER MONDAY MORNING AS THE FRONTAL
BOUNDARY PASSES THROUGH BUT AS THE COOLER SURFACE AIR SETTLES IN
THE INSTABILITY QUICKLY WEAKENS. ANY THUNDERSTORMS THAT LINGER
INTO THE MONDAY AFTERNOON AND EVENING WILL BE ELEVATED.

AS WE MOVE INTO TUESDAY AND THE REST OF THE WEEK THE FRONT
INITIALLY REMAINS STATIONARY NEAR OR JUST SOUTH OF THE REGION
KEEPING A MOIST EASTERLY FLOW AND POSSIBLY THE HIGHEST CHANCE OF
RAIN. BOTH GFS AND ECMWF INDICATE ON AVERAGE THAT TUESDAY WILL
HAVE THE BEST COVERAGE OF RAIN. THIS WILL ALSO KEEP TEMPERATURES
BELOW NORMAL.

AFTER TUESDAY FORECAST TRENDS DOWNWARD ON THE RAIN AND UP
WITH THE TEMPERATURES. THE FRONT EVENTUALLY DISSIPATES OR MOVES
BACK NORTH AS SHORTWAVE RIDGING BUILDS OVER WESTERN TEXAS WITH THE
NEXT UPPER TROUGH APPROACHING THE PACIFIC COAST. GFS AND ECMWF DO
LITTLE WITH THIS TROUGH AND IT LOOKS MUCH WEAKER THEN THE LAST FEW
TROUGHS. SOME PERTURBATIONS DO ADVANCE THROUGH THE TROUGH AND
RIDE ALONG STOUT SOUTHWESTERLY UPPER JET AND MAY SPARK SOME
AFTERNOON CONVECTION OVER THE SIERRA MADRE AND THEN DRIFT INTO OUR
CWA EACH AFTERNOON AND EVENING. THIS WILL BE INDICATED BY LOW
GRADE POPS EACH LATE DAY AND EVENING.

MARINE...NOW THROUGH SUNDAY NIGHT...THE SOUTHEAST WINDS WILL
REMAIN LIGHT TO VARIABLE WITH LOW SEAS ACROSS THE GULF WATERS. THE
MAIN CONCERNED THROUGH THE SHORT TERM WILL CONTINUE TO BE THE
CONVECTION OVER THE GULF. THERE IS ENOUGH INSTABILITY IN THE AREA
FROM A STATIONARY BOUNDARY PARALLEL TO THE COAST THAT WILL ENHANCE
MORE CONVECTION INCREASING LATE THIS AFTERNOON AND CONTINUE
OVERNIGHT. SUNDAY...THE POTENTIAL FOR CONVECTION WILL BEGIN TO
DEVELOP IN THE AFTERNOON AND CONTINUE OVERNIGHT AS A COLD FRONT IS
EXPECTED TO ARRIVED EARLY MONDAY INCREASING THE CHANCE OF RAIN
EVEN MORE AND SHIFTING WINDS NORTHERLY.

MONDAY THROUGH THURSDAY...COLD FRONT STILL ON TAP FOR EARLY
MONDAY AS HIGH PRESSURE BUILDS DOWN THE CENTRAL PLAINS AS A MID
LEVEL TROUGH DEEPENS INTO THE GULF SOUTH STATES. NORTHEAST WINDS
INCREASE APPROACHING SMALL CRAFT ADVISORY CONDITIONS MONDAY
AFTERNOON. SEAS TO RESPOND AND BUILD UPWARDS TO 6 FEET BY MONDAY
NIGHT. MODERATE NORTHEAST TO EAST WINDS PERSIST TUESDAY AS THE
FRONT BECOMES STATIONARY AND HIGH PRESSURE EXPANDS OVER THE
CENTRAL GULF. A RETURN TO SOUTHEAST WINDS WEDNESDAY WITH A GRADUAL
INCREASE THROUGH THE END OF THE WEEK IS EXPECTED. SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS MONDAY AND TUESDAY WITH
DECREASING COVERAGE MID TO LATE WEEK.
&&

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

$$

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