Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 152327

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

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


.AVIATION...Mainly VFR conditions expected for all three
terminals this TAF cycle. A cold front is currently moving through
the region. Winds have already become northerly and in some cases
a bit gusty. Overall it has been dry over all three terminals,
though some shower/storm activity will be possible this evening,
especially for MFE. Covered the outside chances for SHRA over BRO
and HRL with TCs. If a shower or storm comes overhead there would
be an opportunity for reduced vis/cigs briefly. Any rainfall
should be limited after midnight, however, wind gusts up to 20kts
or so may be possible through Monday afternoon.



.PREV DISCUSSION... /issued 243 PM CDT Sun Oct 15 2017/

SHORT TERM (Now through Monday night): Bulk of significant weather
to occur in the first period of the short term as another touch of
fall is slated to impact the forecast area. Satellite imagery was
showing a weak pre-frontal trough draped west to east across the
Corpus Christi forecast area with a southwest to northeast oriented
cold front pushing southeast away from Del Rio and approaching
Carrizo Springs. This front will move through the BRO forecast area
roughly between 7 PM to 1 AM tonight. Moisture with the front
does not look overly impressive and short-term models have backed
off somewhat from previous precip amounts. Because of this, have
trimmed back chances of precipitation for the evening and have
ended them completely over the land portion of the forecast area
by 06Z. Most noticeable with the frontal passage will be the
strengthening of northerly winds and rapidly cooling temperatures
as cooler and drier air advects into the region behind the front.
Gusty northerly winds will continue overnight into the early
morning hours on Monday.

Monday will start off relatively cool for areas over the western
half of the forecast area with places like Zapata starting off in
the lower 50s. Lows over the west will be anywhere from 7 to 12
degrees below normal. However, lows Monday morning near the coast
will be much warmer and much closer to normal. Northerly flow will
prevail but weaken across the region through the day on Monday as
skies clear in response to surface high pressure building over the
Rio Grande Valley. Clouds and cold air advection will keep high
temperatures on Monday generally 5 to 8 degrees below normal
area- wide. Highs will be in the mid/upper 70s along the coast
with mid 80s inland and west. Lows Tuesday morning over the west
will reach similar values from the day before (lower/mid 50s)
while dryer air in place along the coast will allow temperatures
there to drop into the mid/upper 50s.

LONG TERM (Tuesday through Sunday): Nice fall-like weather with
cool mornings and comfortable afternoons will continue through
mid-week in the wake of the cold front early in the week. 500mb
ridging will begin to build in on Wednesday with virtually no rain
chances expected across Deep South Texas. Models continue to show
a weakness on the back side of the ridge from Thursday through
Saturday, which will bring the next chance of precipitation to the
area as deeper moisture returns off the Gulf waters. Time height
profiles show a lot of dry air still in the mid levels with most
of the moisture confined to below 700mb, so not expecting any
widespread precipitation. However, light E/NE flow at the surface
will warrant seabreeze enhancement along and west of the coast
with diurnal differential heating, so have kept PoPs in the 20 to
30% range for now.

Sunday, models begin to diverge greatly with the latest 12Z
guidance. Both the GFS and ECMWF bring a deep, digging trough of
low pressure down into the south central U.S., but placement
varies considerably. The GFS keeps it over the Four Corners region
with the ECMWF bringing it right over central Texas. Both
solutions would bring much higher rain chances, but this is in the
day 7+ period, so have kept the forecast mainly the same due to
low confidence.

Temperatures for the middle of the week will be a few degrees
below normal with lows in the upper 50s to low 60s and highs in
the lower to middle 80s. By the end of the week temperatures and
humidity will return back to normal with highs reaching the lower
90s this weekend across the Upper Valley.

MARINE (Now through Monday night): Modest seas and north flow now
in place across the waters with seas of 2 to 4 feet over the Gulf.
Surface cold front approaching from the north will move across the
waters late this evening with northerly winds increasing. After
sunset, winds will reach into the 20 to 25 knots range with higher
gusts possible to near 30 knots. Small Craft Advisories already in
place for the waters beginning at 7 pm this evening and will likely
be needed through all of Monday. Winds/seas to slowly subside Monday

Tuesday through Friday: Surface high pressure will slide eastward
towards the Mid-Atlantic, which will shift winds back to the east
for much of the period. Seas will quickly drop to 2 to 4 feet
Wednesday into early Thursday. Persistent easterly fetch across
the Gulf waters will eventually build seas back up Thursday
evening and Friday with wave heights approaching 6 feet offshore.


GM...Small Craft Advisory for winds until 1 PM CDT Monday for GMZ130-

     Small Craft Advisory until 1 PM CDT Monday for GMZ150-155-170-



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