Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 151727
AFDBRO

Area Forecast Discussion
National Weather Service Brownsville TX
1227 PM CDT Sun Oct 15 2017

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

&&

.AVIATION...Modest northerly winds, both at the surface and
aloft, are now in place across the entire forecast area in advance
of a cold front and a pre-frontal trough approaching from the
north. As of 1715Z, the front was strung west to east along a CZT-
PEZ-ELA line. The front is anticipated to enter the northern
portion of the forecast area around 22Z then exit the region into
northern Mexico after 04Z. As the front continues to approach this
afternoon, northerly winds will slowly increase in speed. As the
front moves through late this afternoon and evening, it will bring
MVFR conditions, mainly in terms of lowered CIGS, but it will
also bring some showers mainly between 23Z-03Z that will restrict
visibilities at times. VFR conditions are otherwise expected
through the TAF period. Northerly winds will continue to increase
this evening with the passage of the front amidst a tight pressure
gradient. Moderate northerly flow with wind gusts as high as
25-30 kts will continue across Deep South Texas the entire second
half of the TAF period.

&&

.PREV DISCUSSION... /issued 650 AM CDT Sun Oct 15 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Patchy fog and low clouds will occasionally bring
MVFR to brief IFR conditions to terminals through the early
morning before improvement to VFR is noted by mid morning.
Meanwhile, light and variable to light north winds will continue
as a coastal trough moves west. By tonight, a cold front will
sweep through the RGV with gusty north winds expected with
increasing chances for scattered showers and isolated
thunderstorms. The best chances for precip will likely be between
00Z to 06Z this evening, with precip lingering on a bit longer at
KBRO overnight into Monday.

PREV DISCUSSION... /issued 428 AM CDT Sun Oct 15 2017/

SHORT TERM (Today through Monday): Quiet weather has been noted
overnight across deep south Texas and the RGV with areas of fog
developing once again due to abundant soil moisture and light to
calm winds.

Meanwhile, models remain in good agreement for a cold frontal
passage late this afternoon and evening. This front, currently
draped across West Texas early this morning, is progged to steadily
move southward through the day as a sharp H5 trough digs across the
Central Plains. At the same time, a developing low pressure system
over the West-central Gulf will work its way west towards the RGV
today. The preliminary and non-operation GOES-R precipitable water
channel shows PWAT values currently around 1.5" across the region.
However, higher values near 2.0-2.2" is associated with the with low
pressure troughing over the Gulf which will increase low level
moisture along our coastal areas. Do expect shower and some
thunderstorm chances to increase across the Northern Ranchlands by
late afternoon to early evening as the front moves in. Meanwhile,
POPs should increase across the Valley as the moisture increases
with the coastal low moving west and then shifting south as the
front pushes into the RGV this evening. The best chances for precip
across the Valley will likely be between sunset and early Monday
morning. Even so, rainfall amounts should be generally light.

The front will quickly exit south of the Rio Grande late tonight
although lingering moisture and influence of the coastal trough could
keep some low end POPs in places for the Lower RGV and coastal areas
through at least Monday morning. Meanwhile, drier air will be
funneling into the region from the north which eventually ending
precip for the land areas by Monday afternoon.

As far as temperatures go, highs will generally still be in the mid
to upper 80s north to lower 90s south given the FROPA will not occur
until this evening. Temperatures will be noticeably cooler overnight
as the drier, cooler air filters in with lows in the 60s Monday
morning and high about 10 degrees cooler Monday afternoon.

LONG TERM (Monday Night through Saturday): 500 mb ridging will
prevail over the U.S./Mexico border region from Mon Night through
Wed. Weak to moderate CAA will persist through midweek in the wake
of the fropa. This will hold temps close to or just below climo
through Wed. A weakness in the ridge axis will develop starting
Thurs and will persist through Sat. Deep layer tropical moisture
will also start to advect north from the southwestern Gulf of Mex
towards the TX coastline. Most of the better moisture values will
likely remain just offshore of the lower TX coastline late in the
forecast period. However enough of this moisture may push into the
RGV to warrent some mention of slgt chc/chc pops Thurs through
Sat.

After the cool down from the fropa, the temps will start to
steadily warm back up through the weekend as the low level flow
shifts around back from the east to southeast allowing both the
temps and dewpoints to increase.

Both the ECMWF and the GFS model output continues to show good
agreement in the handling of the 500 mb pattern through Day 7.
Also the MOS output from both models remains in good agreement
both for temps and pops. So will stick close to a GFS/ECMWF blend
for the extended period.

Overall forecast confidence in the longer range period remains
above average due to the high model consistency.

MARINE: (Now through Monday):  Light to moderate winds and low to
moderate seas will be in place through through this afternoon. A low
pressure system over the West-central Gulf will move towards the
Lower Texas Coastal waters today with showers and some thunderstorms
possible and increasing north winds will develop. Marine conditions
will become hazardous later as cold front moves through the Lower
Texas Coastal Waters Sunday evening with north winds of 20-25 kts
and seas of 6-8 ft developing into the early morning hours on
Monday. Adverse conditions will continue through the end of the short
term period.

Monday Night through Thursday night: The post front PGF will
remain strong Mon Night and Tues pushing the offshore winds and
seas close to SCA levels. The PGF will then slacken on Wed and
Thurs allowing the winds and seas to fall below SCA criteria.
However as the east to west surface wind flow pattern prevails
over the Gulf of Mex will then rebuild the swwell train across the
Gulf possibly boosting the offshore swells back up close to SCA
levels once again.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...Small Craft Advisory for winds from 7 PM this evening to 1 PM
     CDT Monday for GMZ130-132-135.

     Small Craft Advisory from 7 PM this evening to 1 PM CDT Monday
     for GMZ150-155-170-175.

&&

$$

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

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