Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 192344 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
644 PM CDT FRI AUG 19 2016

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

.AVIATION...Breezy winds at sunset should rapidly diminish to
more moderate levels a couple of hours afterwards with just a
few clouds anticipated overnight. Tomorrow, breezy winds will
resume with scattered cloudiness overhead. Overall, VFR is
expected through the next 24 hours.
&&

.PREV DISCUSSION... /issued 256 PM CDT FRI AUG 19 2016/

SHORT TERM (Now through Saturday): Plenty of dry air mix- down
and enhanced gusty south/southeast winds not only killed off the
rain chances but also pumped up the temperatures which will likely
ease above 100 along/west of U.S. 281/IH 69C and will come close
near U.S. 77. Forecast covers all of this nicely to close the day
so no changes made.

Thereafter, the 500 mb ridge hangs on for all of Deep South Texas
for one more night and part of Saturday before the southern edge of
an elongated trough oriented from east-northeast to west-southwest
across central Texas noses toward the South Texas Brush Country
beginning Saturday afternoon and continuing into Saturday night.
The theme for much of the summer has favored missed opportunities
for the populated Rio Grande Valley, and this event, while
atmospherically different will feature the same sensible weather
result.

This means a gradually increasing chance of rain for the Rio Grande
Plains beginning Saturday afternoon and increasing Saturday night as
better vertical motion links up with deeper moisture and the tail of
the 500 mb trough. There may be a sharp edge to any precipitation as
mean flow up to 500 mb is mainly south to southwest and very dry
layers (mainly from eastern Starr to the Gulf) loom just east of the
deeper moisture to the west.  Elected to add a small buffer of
mentionable rain into McAllen, and along the entire northern tier to
blend with the Coastal Bend where forcing and moisture is a little
more robust.

For the sensible weather, a mainly clear night with breeziness early
and still some pokes of moderate wind late, which will keep
temperatures at or above 80 for much of the Valley even at daybreak,
and raised temperatures a hair to account. For Saturday, the depth
of the dry air keeps rain chances at 10 percent at best from
Hidalgo/Brooks eastward, as another breezy late morning through
afternoon prevails especially across the populated RGV.  This
matches nicely with a GFS-leaning blend of model guidance. Across
the Upper Valley/Rio Grande Plains, the increasing moisture depth
along with lighter winds should allow moisture to "latch on" and
allow at least isolated showers/storms to grow late in the day, but
the southwest to northeast movement should keep outflow influences
away from the larger populations. The thick dry air and warm start
will push highs above the triple digit mark for the Mid/Upper
Valley, and heat index will climb into the 104 to 108 range for most
folks getting ready for the first day of school...but temperatures
will fall short in Zapata/Jim Hogg where mid/high clouds and
potential convection lurk.

For Saturday night, the deeper moisture makes little headway east
but forcing increases, which matches up nicely with the higher rain
chances for the Rio Grande Plains and Upper Valley mainly north of
the river.  Did not push chances into the likely (60 percent)
category but did rise into the 40-50 percent range.  Farther east,
and sharper drop off with continued isolated mention all the way
to McAllen/Brooks County as a buffer. Convective parameters appear
fairly paltry late night so removed thunder mention after
midnight.

LONG TERM (Sunday through Friday):Moisture increases slightly
Sunday in advance of a cold front over North Texas, an upper
level low over Northern Mexico and a mid level inverted trough
over the Southwestern GOM. Residual moisture hangs around Monday
but with the front and the upper level disturbances weakening or
moving farther away from the CWA rain chances to tapper off but
not completely be eliminated. Model guidance remains consistent
with the Western zones having the best chances with higher and
deeper moisture and in closer proximity to the lifting mechanisms.
However...ECMWF does continue to show much higher pops for all
areas over the GFS. Sunday is likely the best chance for rain
before the Bermuda Ridges builds Westward steadily pushing the
deeper moisture westward. 12Z GFS now shows another inverted
trough on the south side of the Bermuda ridge being directed
towards the Texas coast Monday night into Tuesday. ECMWF is weaker
and farther south with the inverted trough and shows center of the
Ridge building farther west. Moisture levels are limited and South
winds may be a bit strong and not conducive for any organized sea
breeze so will keep the forecast dry with exception to the Gulf
coastal waters. Will also keep the rest of the forecast period
(Wed-Fri) dry as the mid level ridge will centered over the
Northwest Gulf with sufficient dry air aloft keeping the rain
chances of rain below seasonal averages. Temperature trends are
subtle but a slight increase is likely mid to late in the work
week as the rain chance wane and the western side of the ridge
builds across the Gulf and Eastern Texas.

MARINE:(Now through Saturday Night): Typical daytime gradient has
pushed the Bay to the edge of Advisory (17 knots or so) this
afternoon, and has popped values way up at the Land Cut to 20 knots
at least for a couple hours. Even the outer Gulf waters have picked
up this afternoon and have briefly reached caution, (17 Gust 20
knots), a hair above forecast. With fairly strong 850 mb flow
overnight and favored nighttime pickups of winds over the Gulf,
we`re coming to the edge of advisory conditions for a 3 to 6 hour
period around midnight to the pre-dawn hours.  Will defer decision
to the next shift when more data is available.

Otherwise, daytime Gulf winds should back down to 13 to 17 knots or
less with the Laguna picking up once again on Saturday to at
least caution levels. The persistent winds are creating
aggravating wind chop and combined seas will rise to 5 feet or
locally higher overnight before gradually subsiding a little on
Saturday and more by Saturday night. Isolated showers return late
Saturday night, otherwise no rain expected.

(Sunday through Wednesday)...Pressure gradient to strengthen
slightly Sunday into Monday as the Western side of the Bermuda Ridge
builds into the Western Gulf.  The gradient then begins to slacken
mid week as the center of the Ridge pushes farther west.  Diurnal
gustiness to provide SCEC over the Laguna Sunday and Monday during
the daytime hours with the higher winds anticipated over the Gulf
during overnight hours especially Monday.
&&

.BRO Watches/Warnings/Advisories...None.
&&

$$

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