Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 262351 AAA

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
651 PM CDT Mon Sep 26 2016

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

.AVIATION...Remaining convection within Deep South Texas and the
Rio Grande Valley is away from the major aerodromes, with mainly
high cloudiness also in place. VFR will prevail through the
overnight hours, with weather forecast models suggesting TEMPO
MVFR in association with showers that may develop over the Lower
Texas coastal waters and then move inland. Tomorrow, VFR will
continue through a majority of the period, with daytime heating
producing another round of convection with TEMPO MVFR, primarily
during the afternoon hours.

.PREV DISCUSSION... /issued 233 PM CDT Mon Sep 26 2016/

SHORT TERM (Now through Tuesday Night): Is it all over except the
shouting? That "shouting" may only be in the form of scattered
showers and perhaps a rumble or two through sunset this evening
as temperatures have nudged to the upper 80s...convective temp...
which has kicked off some resurgence of rainfall. That said,
atmosphere remains worked over this afternoon and not expecting
anything more than welcome brief downpours, though those can be a
nuisance for afternoon/evening drivers.

Thereafter, the threat for locally heavy rainfall is over.  While
deep layer moisture remains stout through midday Tuesday, the
atmospheric wind fields all gradually back to the north/northeast
below 700 mb and the north/northwest above 700 mb...all completed by
Tuesday morning. The flow pattern falls underneath a continuing
upper level ridge; each situation is not conducive to heavy rainfall
production. Thus, have removed said wording from all forecast

All this said, a couple of things to note:  Deep layer moisture
along with some modest heating on Tuesday is enough to keep a
mention of rainfall in the forecast, but stepped back to "showers"
rather than showers/thunderstorms based on the atmospheric flow
pattern and increased stability.  The other item is what occurs
toward the coast?  WPC QPF is rather bold across the Lower Texas
coast, mainly along/east of US 77/IH 69E in Cameron County then
extending closer to the coast of Willacy and Kenedy Counties. With
water temperatures still running in the mid 80s, a northeast low
level component working with the deep moisture is enough to keep
rainfall totals a bit higher, and while nudging the bigger national
QPF forecasts down a bit, we`re still looking at 1/2 to 1 inch on
the balance in these areas from sunset tonight through Wednesday
daybreak.  Significantly lower rainfall totals out toward the
mid/upper Valley and ranchland, with no mention of any rainfall by
Tuesday night in these areas.

The exception for the Rio Grande Plains (Zapata and perhaps
Starr/Jim Hogg) is potential for some bleed-over of any Sierra Madre
activity between sunset and midnight. With no more southerly
training flow, however, see little opportunity for bands of 3 to 6
inches as we saw overnight Sunday.

As for temperatures, today broke the back (for now) of the non-stop
searing heat and the increasing northerly flow and plenty of
clouds,lifting from a low overcast in the morning to higher broken
skies by afternoon, will keep 80s the theme by Tuesday afternoon.
Those same clouds keep overnight temperatures insulated, however,
and most areas will fall to around 70 to the lower 70s, a smidge
above late September averages.

LONG TERM (Wednesday through Monday): Will avoid a sesquipedalian
discussion this afternoon. The models show the driest air lagging to
the north, with a west to east demarcation across central Texas on
Wed, even as H5 ridging builds over the CWA. Enough low level lift,
with a remnant frontal boundary still in the area, and moisture will
be present to keep scattered precipitation in the forecast for Wed
and isolated for Thu. By Thu, reinforcing high pressure from the
plains will push south and will finally bring enough dry air to deep
South Texas to cause a total cessation of mentionable rain, and
slightly cooler, clearer weather Thursday night. Mostly sunny skies
and a slow warming trend will ensue Fri through the weekend.

Now through Tuesday Night...The main story will be continued better
coverage of rainfall and just how strong the north/northeast winds
can get as the high pressure ridge oozes into the waters. Without
much cool air advection the possibility for strong northerly winds
nearing or exceeding Advisory levels (20+ knots) is slim, but past
weak `northers even with limited advection can kick up speeds into
caution (15 to 20 knot) territory, and this may well be the case
across the waters north of Mansfield tonight and in all areas
Tuesday and Tuesday night, particularly west of the 40 nm line. For
now, retained current idea with 15+ knots closer to shore and 10 to
15 knots offshore, and retained the 4 foot seas in similar areas
where wind and fetch of wind is best. No headlines for now, but may
need to add caution Tuesday and Tuesday night.

Laguna Madre winds may also sneak toward 15 knots especially Tuesday
and a brief period of Small Craft Exercise Caution may be required
but for now have held just below these levels.

Wednesday through Saturday...Broad surface high pressure will filter
south from the plains, resulting in light to mdt northeast winds and
low to moderate seas. There will be some general convective activity
over the Gulf Wed and Thu, but less so Fri and Sat.



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