Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 200527 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1127 PM CST Fri Jan 19 2018

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

.AVIATION...Satellite images and surface observations indicate
low clouds and fog across portions of the CWA late tonight.
Ceilings were near 300ft at KBRO/KHBV/KT65 to near 1500ft at KAPY.
Visibilities were near 3/4SM with fog at KT65 to near 6SM with
fog at KMFE. Expect IFR to LIFR conditions to continue to develop
across the Rio Grande valley late tonight into Sat morning as low
clouds and fog continues to reduce ceilings and visibilities.
Ceilings and visibilities will begin to improve after 15Z Saturday
as low clouds and fog begin to lift with diurnal heating.

.PREV DISCUSSION... /issued 552 PM CST Fri Jan 19 2018/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Satellite images and surface observations indicate low
clouds across the most of the CWA early this evening with mostly clear
skies across extreme western portions. Ceilings were near 400ft at
KHRL and KPIL to near 2600ft at KBKS. Visibilities were near 2SM
with fog at KPIL to near 3SM with fog at KHRL. Expect IFR to LIFR
conditions to continue to develop across the coastal sections of
deep south Texas this evening and move further inland tonight as
fog continues to develop. MVFR to IFR conditions will develop
across the western portions of the CWA late tonight into early
Saturday with fog developing farther west.

PREV DISCUSSION... /issued 252 PM CST Fri Jan 19 2018/
SHORT TERM (Now through Saturday night): An early-season warming
trend is upon us, as southerly flow returns to South Texas.
Currently a coastal trough is slowly starting to wrap up and eject
northeastward along the Gulf coast. This continues to provide
light northerly wind flow at the surface. Winds quickly change by
the time you reach 1000 feet off the surface, as modest southerly
flow continues to overrun the very shallow cold pool. With the
northerly flow beginning to weaken, -dz continues to decrease
across the region, leaving continued cloudy and grey skies. Some
thinning of the overcast is noted in the far western valley, and
this should slowly shift across the rest of the valley through the
night. The main threat tonight is fog formation. Winds will
settle after midnight, becoming nearly calm. Temperatures are
forecast to remain steady in the low 50s through the night, so
ample moisture from recent precipitation will help bring hazy
conditions. Some fog may become dense in low-lying areas.
Southerly flow returns promptly tomorrow morning, helping to erode
fog and low clouds in the region. With lows already starting
right around 50, should have no trouble reaching into the 70s (!)
tomorrow afternoon. Ample moisture just off the sfc should keep
skies partly to mostly cloudy through the afternoon. Tomorrow
night may see another round of sea fog developing as winds remain
light onshore and water temperatures remain in the low 50s.

LONG TERM (Sunday through Friday): A return to warmer weather
will occur Saturday and Sunday as mid level ridging moves overhead
and southeast return flow strengthens. Temperatures on Sunday
will be slightly above normal, 76 to 81. Mid level ridging will
shift east late in the weekend as a southern plains storm system
develops. Winds will weaken over the CWA late Sunday, even
shifting to northwest over the brush country and ranchlands late
in the day. The new air mass arriving from the northwest Sunday
night will be from a milder source, basically maritime polar air
from the West Coast, and will therefore have lesser impact than
our recent arctic blasts. Winds will shift to moderate north by
Monday morning with temps right around normal, about 70 during the
day, as the front pushes offshore. Temps will in fact hover close
to normal much of the remainder of the week. A brief chance of
rain will be possible Monday morning with the arrival of the cold
front near dawn, but conditions will then improve through the day.
Due to a stronger offshore push than previously noted, and the
arrival of reinforcing pressure over the northwest Gulf on
Wednesday, the front looks less likely to push back north over the
CWA, although it could end up supporting coastal low pressure,
possibly enhanced by an approaching short wave trough digging
across Texas Wednesday and Thursday. Rain chances, mainly marine
and coastal, will therefore increase from Tuesday evening through
Thursday morning. Onshore flow will eventually become more stable,
east on Friday and southeast on Saturday, as a sharp short wave
trough digs into the southwest United States, supporting a plains
low pressure system. An associated cold front will push into the
area Saturday night.

Now through Saturday night: The coastal trough has begun to exit
to the northeast, leaving out coastal waters with light offshore
flow through this evening. Seas are a bit elevated this afternoon,
due to effects from the trough and windier conditions to the
northeast. Conditions should improve tomorrow as the low departs
and modest southerly flow returns. Will need to watch for some sea
fog development as warmer air moves over waters still in the mid
50s. Current forecast has winds from due south, which are not as
conducive for sea fog. Southeast flow continues to bump up
Saturday night, reaching 15 to 20 knots after midnight.

Sunday through Wednesday night: Winds will strengthen from the
southeast to south Saturday and Sunday as a plains storm system
deepens and tightens the gradient with high pressure which will be
slowly retreating east over the southeast United States. South
winds of 15 to 20 knots will be possible on the Gulf, with
elevated seas poking up to around 7 feet. Winds will weaken late
Sunday ahead of a cold front due Sunday night. The front will
result in north winds of 15 to 20 knots on the Gulf Monday and
Monday night with moderate to high seas. Conditions will improve
somewhat Tuesday and Tuesday night as high pressure spreads over
the area, with light to moderate northeast to east winds. The best
chance for small craft should exercise caution conditions on the
Laguna Madre will be Sunday ahead of the front, with 15 to 20 knot
south winds. Periods of exercise caution conditions will be
possible across the near shore waters through the entire period,
due to a combination of winds and wave heights. The far shore
waters will see 4 to 6 or 5 to 7 feet waves much of the period,
resulting in small craft should exercise conditons to low end
small craft advisory conditions. Strengthening northeast winds
will be possible on Wednesday as the pressure gradient tightens
across the northwest Gulf, with higher seas possible.



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