Area Forecast Discussion
Issued by NWS Brownsville, TX

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000
FXUS64 KBRO 161122 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
622 AM CDT Mon Apr 16 2018

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

&&

.AVIATION...Light southeast winds and clear skies prevail across
deep south Texas this morning. Surface high pressure across the
western Gulf of Mexico will move slowly eastward through the
period. Breezy conditions will develop across the region later
this morning into the afternoon as the pressure gradient
increases. Winds will gradually weaken to around 15 knots after
sunset this evening. VFR conditions expected for the next 24
hours.

&&

.PREV DISCUSSION... /issued 452 AM CDT Mon Apr 16 2018/

SHORT TERM (Now through Tuesday): 500-mb ridge will move
overhead today and tonight with the mid-level ridge axis moving
eastward on Tuesday. Surface high pressure across the western Gulf
of Mexico this morning will move slowly eastward through Tuesday.
Light onshore flow this morning will become breezy later this
morning into the afternoon as the pressure gradient increases. The
00Z BRO sounding is very dry with a PWAT of 0.53 inches. So no
significant cloud cover is expected over the next 24 hours. High
temperatures will reach the low to mid 80s across much of deep
south Texas today and with dewpoints in the 40s and 50s. Breezy
and dry conditions will prevail across the region this afternoon.

Winds are expected to diminish slightly tonight as mixing diminishes
with loss of diurnal heating but moderate southeast winds will
continue across the area tonight. Low temperatures tonight will fall
into the 60s tonight under mostly clear skies. Surface high pressure
across the Gulf of Mexico will interact with low pressure on the lee
side of the Rockies. The tight pressure gradient will support breezy
to windy conditions across eastern portions of the CWA on Tuesday. A
Wind Advisory may be needed for the coastal counties on Tuesday. The
strong onshore flow should support slightly warmer temperatures
across the CWA on Tuesday. High temperatures are expected to range
from the lower 80s near the coast to the mid 90s across the west.

LONG TERM (Tuesday Night through Sunday): With model guidance
remaining in fairly good agreement, forecast thinking is still
similar. SE winds will be in no hurry to diminish Tuesday night,
which, combined with some increase in cloud cover, will keep
Wednesday morning min temps a few degrees above average, generally
in the upper 60s-near 70F. Modest zonal flow at jet-stream level
continues on Wednesday, with afternoon highs similar to those on
Tuesday. Column atmospheric moisture will be mainly confined below
900-875mb, with much drier air above in the layer up to 700mb, so
no mentionable rain chances.

Wednesday night into Thursday, a frontal boundary will pull up
stationary over South-Central TX, or just north of the CWA. An
onshore easterly flow will take shape. This onshore flow may be
enhanced during the afternoon by a sea-breeze. Coupled with slight
upslope flow further inland, will keep mainly slight chance
showers in the forecast. These should be spotty and light in
nature with moisture depth still rather limited. On Friday, the
next lee cyclone will deepen over SE Colorado, tightening the
pressure gradient over Deep South Texas and yielding a breezy to
windy day. The aforementioned front lifts back northward, placing
the area in the warm sector. Low-level moisture is progged to
deepen a bit (going above H85), so slight chance for
showers/thunderstorms still looks reasonable with the subtropical
ridge aloft finally flattening.

Similar sensible weather in store for Saturday...that is, still
breezy and a bit warmer with slight chance to chance PoP`s as a
pre-frontal trough may provide some lift. Better dynamic forcing
and humidity remain to the north (across Central TX), though. Both
the 00Z runs of the GFS and ECMWF bring a Pacific cold front
through sometime on Sunday, with the ECM a bit more bullish on
PoP`s/QPF. At any rate, significantly drier air should move in
behind the front, with current grids showing RH falling below 30%
over the western counties. Too early to get into any fire weather
specifics, though. Min temps behind the front for Monday morning
look to be in the upper 50s-low 60s.

MARINE (Now through Tuesday):  Buoy 42020 reported south-southeast
winds around 14 knots gusting to around 16 knots with seas slightly
under 2 feet with a period of 3 seconds at 310 AM CST/0810 UTC. The
pressure gradient will increase across the lower Texas coast today
as low pressure across west Texas interacts with high pressure over
the Gulf. Light to moderate southeast winds this morning will
increase to moderate this afternoon. Small Craft Exercise Caution
conditions expected on the Laguna Madre today and possibly on the
Gulf waters by late this afternoon. A brief low end Small Craft
Advisory may be possible on the Laguna Madre this afternoon, if
winds are slightly higher than forecast. Winds will continue to
increase on Gulf waters tonight and Small Craft Advisories will
likely be needed for the offshore Gulf waters. Exercise Caution
conditions will continue on the Laguna Madre for tonight. Small
Craft Advisory conditions likely on all waters Tuesday due to
moderate to strong south winds and elevated seas.

Tuesday Night through Saturday: Main periods of marine concern
will be from Tuesday night through Wednesday afternoon and again
Friday and Saturday with an enhanced pressure gradient increasing
SE winds and seas during these periods. Small-Craft Advisories
(SCA`s) likely to be ongoing Tuesday evening for all of the
coastal waters with winds of 20-25 knots. SCA conditions likely to
continue for the Gulf waters for the first part of Wednesday
(with seas building close to 7 ft.) before the gradient slackens
as a front sags into central TX, eventually allowing seas to
relax. Improved marine conditions are expected Wednesday night
through Thursday night as a moderate onshore easterly flow keeps
seas in check, at around 3-4 ft. SSE winds crank up again by
Friday afternoon, though, with Small Craft Exercise Caution
likely through Saturday, with periods of additional SCA possible.

FIRE WEATHER (Today and Tuesday)...The combination of surface high
pressure across the northwest Gulf of Mexico and low pressure over
west Texas will provide a strong pressure gradient across deep south
Texas this afternoon. Temperatures will be in the mid to upper 80s
across the Rio Grande valley this afternoon with dewpoints in the
50s across the lower Valley and in the 40s in the upper Valley. This
will result in erratic wildfire behavior across most of the CWA this
afternoon with 20 mph with higher gusts and relative humidity values
less than 30 percent across deep south TX except across the coastal
sections. Have upgraded Fire Weather Watch, previously in effect, to
a Red Flag Warning for this afternoon. Also, will issue a Fire
Danger Statement for the coastal counties for today.

Erratic wildfire behavior is possible again Tuesday afternoon due to
the combination of gusty southeast winds, dry fuels, warm
temperatures, and low to moderate humidity. For these reasons, have
issued a Fire Weather Watch for Brooks/Hidalgo county west for
Tuesday afternoon.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...Red Flag Warning from 1 PM this afternoon to 8 PM CDT this
     evening for TXZ248>250-252-253.

     Fire Weather Watch from Tuesday afternoon through Tuesday
     evening for TXZ248>250-252-253.

GM...None.
&&

$$

This product is also available on the web at:
HTTP://WEATHER.GOV/RGV

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