Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 191233 AAA
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
733 AM CDT SUN APR 19 2015

.DISCUSSION...FOG IS DISSIPATING RAPIDLY AND VISIBILITIES ARE
IMPROVING EARLY THIS MORNING AS DRIER AIR IS BEGINNING TO MIX OUT
THE FOG. THE DENSE FOG ADVISORY HAS BEEN CANCELED. ALSO DELAYED
THE OUTSIDE OF ANY SHOWER OR THUNDERSTORMS ACTIVITY UNTIL THIS
AFTERNOON SO PLENTY OF SUN THIS MORNING TO GET A UP START TO
THE ANTICIPATED AFTERNOON HEATING. CONVECTION IS STILL PROBABLE
AND WILL BE MONITORED FOR ANY DEEP CONVECTION THAT MAY DEVELOP.

&&

.PREV DISCUSSION... /ISSUED 633 AM CDT SUN APR 19 2015/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...FLIGHT CONDITIONS ARE IMPROVING A LITTLE FASTER THAN
ANTICIPATED THIS MORNING. MORNING BALLOON RELEASE SHOWS DRY AIR
JUST ABOVE THE SURFACE SO EXPECTING A QUICK IMPROVEMENT FOR THE
DAY. SOME RISK OF CONVECTION LATE THIS AFTERNOON BUT IT WILL BE
FIGHTING A STRONG CAP AND CHOSE TO LEAVE IT OUT OF THE TAFS FOR
NOW. FLIGHT CONDITIONS DETERIORATE ONCE AGAIN TONIGHT AS WINDS
SLACKEN AHEAD OF AN APPROACHING FRONT. CONDITIONS WILL LIKELY DROP
FASTER THAN THEY HAVE IN PREVIOUS NIGHTS AND THERE MAY BE SOME
ADDITIONAL SHOWER/THUNDERSTORM ACTIVITY CLOSE TO 12Z. /68-JGG/

PREV DISCUSSION... /ISSUED 406 AM CDT SUN APR 19 2015/

SHORT TERM /NOW THROUGH MONDAY/...

LIGHT WINDS AND CLEAR SKIES HAVE SET THE REGION UP FOR FOG THIS
MORNING. HAVE ALREADY ISSUED A DENSE FOG ADVISORY FOR THE COASTAL
COUNTIES AND MAY NEED TO QUICKLY FOLLOW UP WITH ANOTHER ONE FOR
LOCATIONS INLAND BASED ON 11/3.9 MICRON SATELLITE IMAGERY. DRY AIR
JUST ABOVE THE SURFACE SHOULD HELP THAT FOG LIFT TO STRATUS AND
EVENTUALLY OPEN UP THROUGH THE DAY.

THE LIGHT WINDS APPEAR TO BE A RESULT OF LARGE SCALE CONVERGENCE
ALOFT BEHIND THE DEPARTING UPPER SHORTWAVE TROUGH CURRENTLY OVER
SOUTHEAST TEXAS. A 120 TO 130 KT ZONAL SPEED MAXIMUM JUST BEHIND
THIS TROUGH IS MOVING OVERHEAD AS WE SPEAK AND THE CORE OF IT WILL
BE BASICALLY OVERHEAD DURING THE DAY TODAY. THIS SHOULD HELP DRY THE
MIDDLE ATMOSPHERE AND LEAD TO MOSTLY SUNNY SKIES MUCH OF THE EARLY
PART OF THE DAY ALTHOUGH SOME HIGH CIRRUS/CIRROSTRATUS WILL PROBABLY
FOLLOW THE JET MAXIMUM.

THUNDERSTORM DEVELOPMENT/INITIATION IS THE MAIN QUESTION TODAY.
NAM/GFS/ECMWF REINFORCE A WEAK BOUNDARY THAT BISECTS THE CWA AND
THERE IS FAIRLY GOOD AGREEMENT THAT AT LEAST A CELL OR TWO WILL
INITIATE OVER THE AREA AND MOVE SLOWLY EASTSOUTHEASTWARD THROUGH THE
DAY. RELATIVELY STRONG RESIDUAL CAPPING EXISTS HOWEVER AND WITH THE
LARGE SCALE UPPER ENVIRONMENT FAVORING CONVERGENCE FEEL FAIRLY
CONFIDENT THAT CAPPING WONT GET ANY WEAKER. THE BOUNDARY MAY BE DEEP
ENOUGH TO INITIATE CONVECTION BUT I SUSPECT EVEN IF IT DOES COVERAGE
WILL BE LIMITED AND THE DURATION OF THOSE STORMS WILL ALSO BE
LIMITED BY A RAPIDLY STABILIZING BOUNDARY LAYER AFTER SUNSET. ANY
UPDRAFTS THAT GET GOING AND GET ORGANIZED WILL BE IN A VERY GOOD
ENVIRONMENT WITH MLCAPE VALUES OVER 3000 J/KG AND STRONG DEEP LAYER
SHEAR AROUND 65 KTS BUT I DONT HAVE THE CONFIDENCE IN WIDESPREAD
DEVELOPMENT TO PLAY IT UP SIGNIFICANTLY IN THE GRIDS OR OTHER
PRODUCTS DESPITE THE IMPROVED BUOYANCY THAT WILL LIKELY BE PROVIDED
BY STRONGER HEATING THAN WE HAVE SEEN THE LAST FEW DAYS. WILL LET
THE DAY SHIFT WATCH MESOSCALE CONDITIONS CLOSELY AND INCREASE
MESSAGING IF NECESSARY.

TONIGHT ANOTHER DEEPER BOUNDARY/FRONT GETS PUSHED IN FROM THE
NORTHEAST WHICH WILL LIKELY INITIATE SOME SHOWER AND ISOLATED
THUNDERSTORM ACTIVITY ALTHOUGH THE RISK FOR SEVERE WEATHER APPEARS
LOW. THAT BOUNDARY WILL REMAIN IN THE GENERAL VICINITY THROUGH
MONDAY WHICH WILL PROBABLY LEAD TO ADDITIONAL SHOWERS CLOUD
COVER...COOLER TEMPERATURES AND PERHAPS A THUNDERSTORM OR TWO. NET
INSTABILITY REMAINS WEAK HOWEVER AND SIGNIFICANT CONVECTIVE ACTIVITY
APPEARS UNLIKELY. /68-JGG/

LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...BROAD 500 MB TROFFING
OVER THE CENTRAL PLAINS STATES WILL MAINTAIN A STATIONARY FRONT
NEAR THE RIO GRANDE TUES AND TUES NIGHT. DURING THE LATTER HALF OF
THE WORK WEEK ANOTHER WEST COAST SHORT WAVE WILL DIG ACROSS THE
U.S./MEXICO BORDER REGION WED AND THURS WHICH WILL IN TURN BUILD A
RIDGE AXIS OVER THE RGV THROUGH THE END OF THE WEEK INTO THE
WEEKEND. AS THE 500 MB RIDGE AXIS BUILDS THE BETTER 500 MB PVA AND
OVERALL MOISTURE VALUES WILL BE SHIFTED FURTHER NORTH WHICH WILL
TEND TO LIMIT THE CONV CHANCES A BIT FROM WED ONWARDS.

THE LONGER RANGE TEMPS AND POPS ARE IN PRETTY GOOD AGREEMENT
BETWEEN THE GFS AND THE ECMWF. SO WILL GO WITH A GENERAL 50/50
BLEND OF THE TWO MODEL SETS THROUGH SAT. TEMPS WILL BE CLOSE TO
CLIMO FOR LATE APRIL ON TUES DUE TO THE BETTER CLD COVER AND HIGH
POPS. TEMPS WILL THEN LEAN WELL ABOVE CLIMO FROM WED ONWARDS AS
THE 500 MB RIDGING BUILDS OVER THE REGION AND THE ATMS GRADUALLY
DRIES OUT. OVERALL CONFIDENCE IS ABOVE AVERAGE THROUGH DAY 7.

MARINE...NOW THROUGH MONDAY... MODERATE SOUTH WINDS WILL PERSIST
THROUGH THE DAY TODAY SHIFTING TO THE SOUTHEAST THIS AFTERNOON.
THUNDERSTORMS MAY FORM CLOSE TO THE COAST THIS AFTERNOON AND MOVE
INTO THE NEARSHORE WATERS. A WEAK FRONT PUSHES ACROSS THE COAST
MONDAY SHIFTING THE WINDS TO THE NORTHEAST BUT PREVAILING WINDS ARE
EXPECTED TO REMAIN BELOW ADVISORY CRITERIA. SHOWERS AND A FEW
THUNDERSTORMS WILL BE POSSIBLE SUNDAY NIGHT AND MONDAY.

MONDAY NIGHT THROUGH THURSDAY...A MODERATE NORTHEAST TO EAST FLOW
WILL PREVAIL MONDAY NIGHT AND TUES WITH THE STATIONARY FRONT
HANGING JUST TO OUR SOUTH. AS THE OLD FRONT DISSIPATES A LIGHT TO
MODERATE SOUTHEAST FLOW WILL REDEVELOP OVER THE LOWER TX
COASTLINE. THIS OVERALL PATTERN WILL MAINTAIN MODERATE GULF SWELLS
THROUGH THURSDAY. NO SCA CONDITIONS EXPECTED THROUGH THURSDAY.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  86  72  77  71 /  20  40  40  40
BROWNSVILLE          87  72  78  70 /  30  40  40  50
HARLINGEN            90  71  80  69 /  30  40  40  40
MCALLEN              92  72  80  69 /  30  40  40  50
RIO GRANDE CITY      94  71  80  67 /  20  40  40  50
SOUTH PADRE ISLAND   79  72  76  71 /  20  40  40  40

&&

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

$$

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

59...SHORT TERM


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