Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 292334 AAA
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
634 PM CDT MON JUN 29 2015

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

.AVIATION...SATELLITE AND RADAR IMAGES AS WELL AS SURFACE
OBSERVATIONS INDICATE ISOLATED CONVECTION ACROSS THE EXTREME
NORTHERN PORTIONS OF THE CWA EARLY THIS EVENING.
OTHERWISE...MOSTLY CLEAR SKIES WERE ACROSS THE CWA WITH A FEW MID
TO HIGH LEVEL CLOUDS. EXPECT VFR CONDITIONS TO PREVAIL TONIGHT
INTO TUESDAY EVEN AS SHOWERS DEVELOP LATE TONIGHT INTO TUES
MORNING ACROSS PORTIONS OF THE RIO GRANDE VALLEY AS A WEAK 500MB
LOW/INVERTED TROUGH ACROSS NORTHEAST MEXICO CONTINUES TO BRING LOW
TO MID LEVEL MOISTURE ACROSS THE WESTERN GULF OF MEXICO INTO THE
CWA.
&&

.PREV DISCUSSION... /ISSUED 302 PM CDT MON JUN 29 2015/
SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/...A SURGE IN MOISTURE
THE PERSISTENT WEAKNESS ALOFT AND DAYTIME HEATING ALLOW FOR
ANOTHER INCREASE IN PRECIPITATION TUESDAY. THE TOTAL PRECIPITABLE
WATER WATER MICROWAVE IMAGERY LOOP INDICATES AN AREA OF 2-2.25
INCH PWATS OVER MUCH OF THE SOUTHERN GULF CURRENTLY. VISIBLE
SATELLITE LOOPS SHOW ON GOING CONVECTION OFF THE EASTERN COAST OF
MEXICO WHICH IS SLOWLY DRIFTING NORTHWARD AS SOUTH TO
SOUTHEASTERLY FLOW STRENGTHENS BETWEEN BROAD HIGH PRESSURE OVER
THE EASTERN GULF AND LOWER PRESSURE ACROSS THE BAY OF CAMPECHE.
MID LEVEL SHEAR ZONE EXTENDING FROM A WEAK 50H LOW OVER INTERIOR
MEXICO THROUGH SOUTHERN AND EASTERN TEXAS TO MAINTAIN A WEAK
DIFFLUENT FLOW AND UPPER SUPPORT. THIS DIFFLUENT FLOW STRENGTHENS
TUESDAY INTO WEDNESDAY AS HIGH PRESSURE OVER THE INTERIOR WEST
EXTENDS INTO WEST TEXAS AND THE MID LEVEL LOW OVER MEXICO DEEPENS.

WARM RAIN PROCESSES AND INCREASING MOISTURE CONVERGENCE TONIGHT TO
INITIATE OFFSHORE AND COASTAL CONVECTION TONIGHT INTO TUESDAY
MORNING. THEN AS DAYTIME HEATING COMMENCES AND THE INSTABILITY
INCREASES CONVECTION SHOULD INCREASE IN AREAL COVERAGE SPREADING
WESTWARD. WILL MENTION HEAVY RAIN IN THE FORECAST ZONES/GRIDS WITH
THE TROPICAL NATURE OF THE AIRMASS A BLEND OF THE MODEL GUIDANCE
STILL LOOKS REASONABLE WITH A LARGE WIDESPREAD AMONG GFS/NAM/ECMWF.

LOW TEMPERATURES WILL BE BUMPED UP A DEGREE OR TWO AND HIGHS TUESDAY
LOWERED A FEW DEGREES WITH THE ADDED MOISTURE. THE NAM AND ECMWF
MODELS FOLLOW THIS TREND WHILE THE GFS REMAINS PERSISTENT WITH
ITS DRIER BIAS.

LONG TERM /WEDNESDAY THROUGH MONDAY/...BROAD RIDGE REMAINS OVER
THE WESTERN PORTION OF THE STATE WHILE UPPER TROUGH DIGS SOUTHWARD
WEDNESDAY. BIG CHANGES ON THE LATEST KBRO 12Z GFS MODEL RUN SHOWS A
MORE ELONGATED RIDGE EXTENDING AS FAR SOUTH INTO DEEP SOUTH TEXAS AND
AS A RESULT KEEPING THE LOW OVER MEXICO FURTHER SOUTH. THIS BRINGS
DRY AIR INTO THE AREA LIMITING THE POTENTIAL FOR RAIN WHICH IS A BIT
DIFFERENT THAN THE PREVIOUS TREND. THERE IS STILL MOISTURE IN THE AREA
TO ALLOW FOR CONVECTION TO INITIATE WEDNESDAY AFTERNOON SO LEAN TOWARDS
HIGHER POPS RIGHT OVER THE LOWER VALLEY. INTO THURSDAY A BIT MORE MOIST
AIR SURGES INTO THE AREA AS BROAD LOW TRIES TO BUILD. A SHORTWAVE
TO THE NORTH AS IT MOVES FURTHER SOUTH STRENGTHENS THE PRESSURE
GRADIENT AND RESULT IN DEEPENING LOW PRESSURE OVER MEXICO. EXPECT
AN INCREASE IN SE FLOW ACROSS THE AREA THURSDAY AFTERNOON WITH AN
ISOLATED CHANCE OF SHOWERS DEVELOPING. TEMPERATURES WILL REMAIN
NEAR NORMAL WITH BIT MORE SUNSHINE THROUGH FRIDAY.

FOR THE WEEKEND...A TROPICAL WAVE OVER THE BAY OF CAMPECHE CONTINUES
TO SHOW A TRAJECTORY ACROSS THE BAY OF CAMPECHE INTO THE WESTERN
GULF COAST AND INTO OUR AREA LATE SATURDAY NIGHT INTO SUNDAY. THE
MODELS CONTINUE WITH THIS TREND WITH DEEP MOISTURE EXTENDING
THROUGH 500 MB IN THE LAYER. LEAN TOWARDS INCREASING POPS CLOSER
TO 50 PERCENT FOR SUNDAY AS WOULD EXPECT SCT COVERAGE THROUGH THE
AREA AND GRADUALLY LOWERING INTO MONDAY AND TUESDAY TO 20 PERCENT
AS THE DEEPER MOISTURE CONTENT RESIDES FURTHER SOUTH.

MARINE...NOW THROUGH TUESDAY NIGHT/...BROAD SURFACE HIGH
PRESSURE TO COMBINE WITH THE LOWER PRESSURE OVER THE BAY OF
CAMPECHE AND EASTERN MEXICO TO MAINTAIN A LIGHT TO MODERATE
SOUTHEAST FLOW. SEAS TO REMAIN AT LOW TO MODERATE LEVELS. A SLIGHT
STRENGTHENING OF THE GRADIENT TUESDAY NIGHT INTO EARLY WEDNESDAY
AS PRESSURES LOWER OVER MEXICO. THIS SLIGHT TIGHTENING OF THE
GRADIENT WILL NOT BE APPRECIABLE ENOUGH AT THIS TIME TO INCREASE
WINDS AND SEAS TO SCEC OR SCA CONDITIONS. THE INCREASE IN
SOUTHERLY FLOW WILL HOWEVER ALLOW A SURGE OF MOISTURE INTO THE
LOWER TEXAS COASTAL WATERS INCREASING THE SHOWERS AND
THUNDERSTORMS. SCATTERED TO POSSIBLE NUMEROUS ACTIVITY IS
ANTICIPATED IN THE SHORT TERM.

WEDNESDAY THROUGH SUNDAY...SOUTHEASTERLY FLOW WILL REMAIN IN
CONTROL STRENGTHENING THE PRESSURE GRADIENT THURSDAY WITH THE
POTENTIAL TO SEE SCEC CONDITIONS CLOSE TO SCA. THERE IS AN
INCREASE IN MOISTURE CONTENT ACROSS THE GULF WATERS AS A TROPICAL
WAVE MOVES ACROSS THE AREA. THIS WILL INCREASE THE POTENTIAL FOR
RAIN SATURDAY DURING THE DAY AND SUNDAY THROUGH THE DAY
DIMINISHING DURING THE OVERNIGHT WITH MORE ISOLATED.
&&

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

$$

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