Area Forecast Discussion
Issued by NWS Brownsville, TX

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000
FXUS64 KBRO 150901
AFDBRO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
401 AM CDT WED APR 15 2015

.SHORT TERM /NOW THROUGH THURSDAY/...A FRONT PUSHED THROUGH THE CWA
YESTERDAY AND CURRENT SATELLITE IMAGERY SHOWS SOME CLEARING OVER THE
RANCHLANDS AND BRUSH COUNTRY...BUT INDICATIONS ARE THAT UNSETTLED
WEATHER IS NOT OVER IN THE SHORT TERM. CONDITIONS MAY TAKE A PAUSE
TODAY AT LEAST...WITH PARTLY TO MOSTLY CLOUDY SKIES AND HIGH TEMPS
IN THE LOWER 80S FOR MOST AREAS. RESIDUAL LLVL MOISTURE AND ENERGY
IN THE STILL SOUTHWEST FLOW ALOFT WILL PROBABLY BE ENOUGH TO TRIGGER
A FEW SHOWERS AND THUNDERSTORMS BY THIS AFTERNOON...HOWEVER.

AFTER A BRIEF PAUSE IN THE ACTION TDY...CONDITIONS WILL DESTABILIZE
AGAIN MOVING FORWARD INTO TONIGHT AND THURSDAY. AN UPPER LOW WILL
SINK INTO THE FOUR CORNERS REGION...WITH SOUTHWEST FLOW REMAINING
ABOVE THE LOCAL AREA...AND JET SUPPORT IN THE UPPER ATMOSPHERE ABOVE
THAT. LOW LEVEL MOISTURE WILL REMAIN SUBSTANTIAL AND AVAILABLE FOR
CONVECTION. AN INCREASE IN DAYTIME SURFACE TEMPS INTO THE MID 80S
THURSDAY WILL ALSO SUPPORT DESTABILIZATION AND OVERTURNING. DAMAGING
WINDS AND HAIL WITH LOCALLY HEAVY RAINFALL WILL BE POSSIBLE THURSDAY
AS SPC PLACES A GENERAL/SLIGHT/ENHANCED CONVECTIVE OUTLK FROM SOUTH
TO NORTH OVER THE CWA. WITH THE CONTINUED CONVECTIVE ACTIVITY WHICH
WILL EXTEND INTO THE LONG TERM...A FLASH FLOOD WATCH MAY BE NEEDED.
WILL HOLD OFF ON THAT DISCUSSION FOR NOW AS DAY SHIFT WILL BE IN A
BETTER POSITION TO ASSESS THE NECESSITY...INCLUDING THE TIMING AND
EXTENT.

.LONG TERM /THURSDAY NIGHT THROUGH THROUGH TUESDAY/... ESPECIALLY
ACTIVE PATTERN PERSISTS WITH DAILY RISKS FOR SEVERE THUNDERSTORMS
AND POSSIBLY FLASH FLOODING EACH DAY THROUGH MONDAY...UNLESS THE
ECWMF IS RIGHT...AND I THINK IT MIGHT BE...IN WHICH CASE THE CHANCE
PERSISTS THROUGH THE WEEK.

GFS/NAM/ECMWF ARE IN PRETTY GOOD AGREEMENT WITH THE SYNOPTIC PATTERN
WITH THU NIGHT/FRIDAY A LARGE RUMBLING CLOSED UPPER LOW OVER THE
FOUR CORNERS REGION AND A LEADING JET MAXIMUM ROUNDING ITS BASE FROM
LOUISIANA TO THE SOUTHERN TIP OF THE BAJA CALIFORNIA. THIS KEEPS THE
TRAIN OF STRONG LOW AND MID LEVEL MOISTURE POURING INTO THE REGION.
DOWNSLOPING 800-700MB SOUTHWESTERLIES DO BUILD A CAPPING INVERSION
WHICH WILL MUDDY THE WATERS A BIT.  HOWEVER STRONG LARGE SCALE
ASCENT ASSOCIATED WITH GOOD SPEED DIVERGENCE AND DIRECTIONAL
DIFFLUENCE COUPLED WITH WEAK WARM AIR ADVECTION IN THE LOWER LEVELS
SHOULD LIFT THIS CAP AND STEEPEN OUR LAPSE RATES. RICH LOW LEVEL
MOISTURE WITH DEWPOINTS IN THE LOW TO MID 70S YIELD ABOUT 3000 J/KG
OF MLCAPE ON FORECAST SOUNDING WITH A LITTLE BIT LESS SATURATED
PROFILE LOOKING A LTITLE MORE FAVORABLE FOR DAMAGING WIND GUSTS AND
LARGE HAIL THAN OUR LAST FEW SETUPS. FOR THE FORECAST PAINTED BETTER
POPS A LITTLE FURTHER NORTH...WHICH SEEMS TO LINE UP WELL WITH WHERE
THE GFS/ECMWF CONVECTIVE PARAMETERIZATION IS SETTING
OFF...PRESUMABLY FROM THE EFFECTS OF DRY/WARM AIR IN THE MID LEVELS
POSSIBLY KEEPING THE CAP IN PLACE. SPC HAS THE ENTIRE AREA IN A
SLIGHT RISK/15% COMBINED THREAT FOR DAY 3 AND I HAVE ZERO ARGUMENT
WITH THAT. THE ACTUAL CHANCE OF STORMS IS A LITTLE HIGHER AROUND
HEBBRONVILLE AND FALFURRIAS BUT IF STORMS DEVELOP THEY COULD BE
SEVERE ANYWHERE WITH LARGE INSTABILITY AND FAVORABLE SHEAR PRESENT.
THE RISK FOR FLASH FLOODING WILL ALSO BE PRESENT ALTHOGUH RAINFALL
RATES MAY NOT BE QUITE AS EFFICIENT WITH PAST STORMS WITH A SLIGHTLY
LESS SATURATED COLUMN PRESENT AND THE STORMS WILL LIKELY BE A LITTLE
FASTER MOVING. PREVIOUS DAYS CONVECTION BOTH TODAY AND TOMORROW MAY
ALTER AVAIABLE INSTABILITY SO KEEP TUNED FOR UPDATES.

SATURDAY APPEARS TO FEATURE ANOTHER RISK FOR STRONG TO SEVERE STORMS
WITH THE LEFT FRONT REGION OF A 130 KT WEST NORTHWESTERLY JET MAX
MOVING OVER THE AREA COUPLED WITH TEH BASE OF AN INCREASINGLY
NEGATIVELY TITLED SHORWTAVE TROUGH AS THE PREVIOUSLY MENTIONED FOUR
CORNERS LOW BEGINS TO OPEN UP. THIS WEST NORTHWESTERLY FLOW IS OUR
MOST CLIMATOLOGICALLY FAVORABLE FOR SEVERE WEATHER BUT AT LEAST IN
GFS PROJECTIONS AN 850MB TROUGH SETS UP JUST BEFORE PEAK HEATING
THAT BRINGS IN NORTHWESTERLY 850MB WINDS AND MUCH DRIER AIR THROUGH
THAT LAYER WHICH MIGHT MAKE CONVECTIVE INITIATION TOUGHER. THE ECMWF
DOES GO AHEAD AND GENERATE PLENTIFUL CONVECTION AND THE GFS ALSO
STILL GENERATES SOME. THE POSSIBILITY OF WIDESPREAD CONVECTION IN
PREVIOUS DAYS OBVIOUSLY WILL WEIGH INTO FINAL SEVERE WEATHER
POTENTIAL AS WELL. THE GIST OF MODEL CONSENSUS HOWEVER IS THAT THERE
WILL STILL BE FAVORABLE LARGE SCALE ASCENT AND SURFACE MOISTURE AND
HEATING COUPLED WITH FAVORABLE SHEAR PROFILES AND WE WILL NEED TO
WATCH CLOSELY FOR SEVERE WEATHER POTENTIAL.

SUNDAY THE ZONAL JET SITS OVERHEAD WITH 250MB SPEEDS AROUND 125KTS.
THERE IS SOME UNCERTAINTY TO HOW MUCH MOISTURE WILL BE AVAILABLE IN
THE 850MB LAYER WHICH MAY PLAY A ROLE IN STORM ORGANIZATION BUT
GFS/ECMWF BOTH INITIATE THUNDERSTORMS OVER DEEP SOUTH TEXAS ALONG A
SURFACE FRONT THAT WAS GENERATED BY THE PUSH OF THIS NORTHWESTERLY
UPPER LEVEL JET. THIS IS ANOTHER PRETTY CLIMATOLOGICALLY FAVORABLE
SEVERE WEATHER PATTERN SO...LIKE BROKEN RECORD WE WILL NEED TO WATCH
FOR THE POTENTIAL ON THIS DAY.

MONDAY THE GFS SENDS THAT FRONT THE REST OF THE WAY THROUGH THE AREA
DRYING AND COOLING THE SURFACE ENOUGH THAT NO STORMS APPEAR TO
DEVELOP UNDER THE STRONG ZONAL JET STREAK BUT THE ECMWF ACTUALL HAS
ANOTHER SHORTWAVE TROUGH PUSHING THROUGH AND GENERATE WIDESPREAD
SHOWERS AND THUNDERSTORMS. PREFER THE ECMWF GIVEN THE VERY
PROGRESSIVE UPPER LEVEL PATTERN IN PLACE LAST WEEK AND KEPT SHOWER
AND STORM CHANCES IN THE FORECAST BOTH TUESDAY AND WEDNESDAY. AT
THIS POINT THE BEST STRATEGY MAY BE TO TAKE THE THUNDERSTORM CHANCES
OUT WHEN WE QUIT GETTING THUNDERSTORMS EVERY DAY.

MAX TEMPS RUN INTO THE MID TO UPPER 80S BEFORE CONVECTION STOPS THE
UPWARD PROGRESSION EACH DAY. /68-JGG/


&&

.MARINE...
TODAY THROUGH THURSDAY...A FEW COASTAL SHOWERS WILL BE POSSIBLE
TODAY WITH AN OLD FRONTAL BOUNDARY JUST OFFSHORE. LIGHT NORTHEAST
WINDS WILL STRENGTHEN TO MODERATE SOUTHEAST TONIGHT AS HIGH PRESSURE
REESTABLISHES ACROSS THE NORTHWEST GULF. SEAS WILL REMAIN LOW TO
MODERATE. UNSETTLED WEATHER WILL CONTINUE...WITH SHOWERS AND
THUNDERSTORMS POSSIBLE.

THURSDAY NIGHT THROUGH MONDAY... MODERATE SOUTHEASTERLY WINDS ARE
FORECAST THROUGH FRIDAY...AND THEN A WEAK FRONT APPRAOCHES THE AREA
BECOMING STATIONARY SOMEWHERE IN THE AREA THROUGH THE WEEKEND. LIGHT
TO MODERATE WINDS ARE EXPECTED WHETHER OR NOT THE FRONT PASSES BUT
THE EXACT WIND DIRECTION WILL BE DIFFICULT TO PIN DOWN THROUGH THE
WEEKEND. THERE ARE HEALTHY CHANCES FOR SHOWERS AND
THUNDERSTORMS...INCLUDING STRONG THUNDERSTORMS IN THE FORECAST
THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  79  73  83  74 /  40  20  30  20
BROWNSVILLE          80  73  84  75 /  40  30  20  20
HARLINGEN            81  72  86  74 /  40  30  30  20
MCALLEN              82  72  88  74 /  40  20  20  20
RIO GRANDE CITY      81  71  89  74 /  30  20  20  30
SOUTH PADRE ISLAND   77  73  80  74 /  40  20  30  20

&&

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

$$

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