Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 210533 AAB

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
1233 AM CDT THU JUL 21 2016

.DISCUSSION...Updated for latest aviation discussion below.


.AVIATION...VFR conditions to prevail overnight and through the
day Thursday. Isolated convection to develop over the Gulf of
Mexico overnight and attempt to move inland around or shortly
after sunrise. Probabilities are low and confidence below average
if any shower or thunderstorm will move over the air terminals so
will mention vicinity in the TAFs at this time. If any convection
does impact the aerodromes it will likely be brief with only short
duration of MVFR at worst. Light East to Northeast flow with gust
up to 20 knots possible.


.PREV DISCUSSION... /issued 650 PM CDT WED JUL 20 2016/

DISCUSSION...Updated for latest 00z aviation discussion below.

AVIATION...A quiet start to the forecast, then a few bumps
possible moving into Thursday morning and into the early to mid
afternoon. Advertised thickening dry air has pretty much erased
all shower activity early this evening with VFR clear skies and
quickly diminishing winds to follow by 9 PM. On Thursday,
previously mentioned weak disturbance (upper shear axis) slides
from east to west along and just south of the Rio Grande. Recent
trends have been to keep the highest moisture and vertical motion,
along with the inevitable thunderstorm clusters, some 20 miles
south of the border. Trying to slice the forecast too thin more
than 12 hours out would be too risky at this point, and based on
the inherited forecast with "scattered" precipitation elected to
add PROB30 groups with MVFR visibility in thunderstorms for all
three terminals, favoring Brownsville and Harlingen from late
morning through early afternoon and McAllen from early to mid

The latest GFS eases the deepest moisture further south by mid to
late afternoon, so removed rain chances from the TAF which makes
sense when sea breeze climatology is added to the mix. That sea
breeze will also enhance winds for the late afternoon, just as we
saw today, with gusts nearing 20 knots at times.

PREV DISCUSSION... /issued 311 PM CDT WED JUL 20 2016/

SHORT TERM (Tonight through Thursday Night): A persistent ridge
of strong high pressure is sitting across the CONUS...bringing
dangerous heat to many locations. While this does not bode well
for many northern states...the high pressure`s placement lends
itself to a much better situation for Deep South Texas and the
RGV. A more moisture rich atmosphere than allowing for better
chances for convective activity.

A upper level disturbance/weakly inverted trough will begin pushing
west to north west across the Gulf late tonight and eventually over
the coast and farther inland through the day on Thursday. There will
likely be an enhanced sea breeze component to the shower and
thunderstorm activity and have increased POPs a bit more through
the afternoon period.

Meanwhile...for temperatures...above normal readings or still
on going despite the uptick of cloud cover and precipitation. It
reached 100 degrees at McAllen once again this afternoon...making it
22 day in a row for consecutive 100+ degree days. This is the 4th
highest. With the anticipated shower and storm activity we stand a
chance of ending that streak...and seeing lower temps overall.
However...much depends on the how quickly the rain and clouds build
into the region.

LONG TERM (Friday through Wednesday): Ridge remains anchored
across the southern US, centered over Oklahoma. Over the weekend
the ridge slowly stretches East-West, with weakness developing
across the central US. The weakness will be in the vicinity over
the weekend into early next week, so the low chances of seabreeze
showers will continue each afternoon for the inland areas, and
during the late night and early morning hours along the coast and
offshore. A larger inverted trough sweeps westward across the gulf
early next week, arriving locally by Wednesday. This will continue
to produce seabreeze showers locally, but may slightly increase
the areal coverage for the midweek period. With continued minimal
chances for rain and variable cloud cover, will continue with the
hotter conditions through the forecast period, with highs around
100 each afternoon and lows in the upper 70s.


Now through Thursday night: Strong high pressure system anchored
over the Central U.S. is causing a long easterly fetch over the
Gulf which in turn is driving 3 to 4 feet swell as indicated at
Buoy 42020. A brief period of 5 ft swells may occur in the far
southeast quadrant overnight. Seas will begin to relax a bit on
Thursday as the high pressure system weakens and retreats west
and alters the winds field to reduce the fetch. Even so...moderate
seas of 3 feet will be noted. There will be a better chances for
showers and a few thunderstorms for the overnight hours and
through the day Thursday.

Tuesday through Monday night: Southeast winds continue into the
weekend with the usual Summer ridging across the Gulf. This will
keep seas steady 2 to 3 feet through Sunday. Showers are possible
late overnight each night, continuing into the morning hours
before dissipating and moving onshore.


BAYVIEW/PORT ISABEL  79  93  79  93 /  10  20  10  20
BROWNSVILLE          77  94  78  94 /  10  20  10  20
HARLINGEN            76  97  77  96 /  10  20  10  20
MCALLEN              76  99  77 101 /  10  20  10  20
RIO GRANDE CITY      76 101  77 102 /  10  20  10  20
SOUTH PADRE ISLAND   80  86  80  85 /  20  20  10  20


.BRO Watches/Warnings/Advisories...


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