Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 221138 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
638 AM CDT Sun Oct 22 2017

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

.AVIATION...Surface observations suggest that patchy fog and areas
of low cloud decks have developed. However, in-situ web cameras
indicate that the fog is likely confined to near ground level, so
MIFG has been placed in the current issuance of TAFs along with
the low clouds. Veering and increasing winds will occur as a cold
front approaches and sweeps through the area. VFR should prevail
beginning after sunrise this morning and then remain in place
through the day and overnight hours tonight.

.PREV DISCUSSION... /issued 344 AM CDT Sun Oct 22 2017/

SHORT TERM (Now through Monday): The most recent surface
analysis indicates a cold front from roughly Bonham to San Angelo
to El Paso. This front is expected to sweep through Deep South
Texas and the Rio Grande Valley today, producing generally
isolated showers and thunderstorms from about sunrise to sunset.
After the passage of the cold front, a massive influx of dry air
and a mid-level flow out of the northwest will produce dry weather
tonight and Monday. Above normal temperatures today in advance of
the front will be tempered to more near normal values tonight and
Monday in the wake of the front.

LONG TERM (Monday Night through Saturday): Models are in pretty
good agreement with the synoptic pattern through most of the week
with deep troughing of low pressure across the eastern half of
the country with ridging centered over southern California.
A series of storm systems will track through the northern Plains
and Great Lakes, which will continue to bring cold fronts through
the eastern half of the U.S. and as far south as Deep South

The first several days of the long term will be pleasant with
warm and comfortable afternoon highs and cool morning lows,
thanks to very dry air settling in through early Thursday. Besides
temperatures, the rest is fairly benign with virtually no rain
chances. Models show precipitable water values dropping to 0.50"
or lower, which would near record low moisture for late October.
Any notable moisture will be confined to below 850mb, which would
make it very difficult for convection to develop, especially with
moderate north winds throughout the column. Early Thursday,
surface high pressure will move off to the eastern Gulf, veering
winds back to the S/SE. Temperatures and humidity will quickly
increase and return back to normal with highs in the upper 80s for
most of the area.

Friday and beyond, models begin to diverge. The GFS brings our
next cold front Friday afternoon with a much deeper low pressure
system over the Great Lakes, and the ECMWF brings the front
through on Saturday with a much weaker system. Decided to go with
a late-Friday passage, but with modest confidence. Model guidance
is showing much lower 1000-500mb thicknesses with this front, so
timing will be very important with regard to the temperature
forecast. Dropped temperatures a few degrees on Saturday with MOS
guidance showing highs only reaching the low 70s in some areas
with lows on Sunday morning in the 50s. Similar to the last front,
it appears there won`t be much of a deep moisture return, so rain
chances are fairly low. Have kept mainly isolated PoPs for the
coastal and marine areas with this package.

MARINE (Now through Monday): The passage of a cold front through
the Lower Texas coastal waters today will increase winds and build
seas beginning late this afternoon and lasting through the overnight
hours. Thus, a Small Craft Advisory has been raised for this time
period for the Laguna Madre and Gulf of Mexico waters east of Padre
Island. Sea heights may remain raised enough on Monday to require
the continuation of the Advisory for the nearshore and/or offshore
Gulf of Mexico waters for a portion or all of the day.

Monday night through Friday: Moderate north winds will continue
on Tuesday with reinforcing high pressure bringing another shot of
stronger north winds Tuesday afternoon into Wednesday with Small
Craft Advisories possible. Winds and seas will briefly improve on
Thursday as surface high pressure moves into the eastern Gulf and
south winds return. Seas will likely deteriorate again just ahead
and behind the next cold frontal passage on Friday. Advisories
will again be possible through the weekend.

GM...Small Craft Advisory for winds from 5 PM this afternoon to 7 AM
     CDT Monday for GMZ130-132-135.

     Small Craft Advisory from 5 PM this afternoon to 7 AM CDT Monday
     for GMZ150-155-170-175.


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