Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 260532 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1232 AM CDT Tue Sep 26 2017

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

&&

.AVIATION...Brownsville radar indicates a few showers moving
northwest across the lower Texas coastal waters early this
morning. Mostly VFR conditions expected through the next 24
hours, with exception of some brief MVFR ceilings around sunrise
from any streamer showers that may develop over the Gulf waters
and move inland. Isolated to scattered showers and thunderstorms
are expected across deep south Texas later today. Light southeast
winds overnight will become moderate this afternoon with some
gusts approaching 20 knots. Winds will diminish to around 10 knots
or less by late this evening.

&&

.PREV DISCUSSION... /issued 620 PM CDT Mon Sep 25 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Generally, VFR conditions are expected for all
terminals through this TAF cycle. Winds will decrease shortly
after sunset this evening, however, gusty conditions can be
expected again by mid-morning on Tuesday.

Mid and upper level clouds will likely begin to increase with time
Tuesday afternoon and can`t rule out a shower or storm, especially
for the McAllen terminal. At this time, confidence is rather low
so only included VCs for now. If convection does indeed occur,
expect brief reduction in cig/vis.

PREV DISCUSSION... /issued 241 PM CDT Mon Sep 25 2017/
SHORT TERM (Now through Tuesday night): South Texas remains
between the H5 ridge just offshore and the large-scale along the
Rockies. Morning sounding showed PW values of 2.02 inches, which
is similar to GOES16 sounder readings this afternoon. As the ridge
shifts east slightly late tonight, the leading edge of the trough
will begin to push more moisture into the region aloft. Along
with this will be shortwave impulses rotating through the region,
adding instability to the atmosphere. Tonight, rain chances will
remain low, as surface forcing will be minimal with no boundaries
to work with. Tomorrow will see a better shot for showers and
thunderstorms as the next shortwave arrives and influences the
seabreeze. Best chances for rainfall will be further inland closer
to the trough, once the seabreeze gets moving. Increased cloud
cover closer to the surface and increased cirrus aloft will hold
temps down a couple degrees from today, but will still reach the
low to mid 90s ahead of the advancing seabreeze.

LONG TERM (Wednesday through Monday):

A cut off low should set up over the southwest United States by
Wednesday while ridging centered over the northwest Gulf spreads
out. A persistent weak background of surface high pressure will
continue over the north Gulf, providing a moderate east flow for the
CWA. Plains high pressure will push a weak front into north Texas on
Thursday. The front will arrive Thursday night with a local wind
shift to northeast. The front will push offshore on Friday. High
pressure will move out of Canada over the Great Lakes on Friday, a
portion of which will ultimately spread south over the lower
Mississippi Valley and into east Texas and the northwest Gulf,
reinforcing the ongoing high pressure pattern and prolonging
northeast winds. The proximity of the cut off low could provide a
higher strong weather threat to the upper valley in the early stages
of the long term, but the models seem less eager to do so today
compared to yesterday. Nonetheless, slightly higher pops were
retained for portions of the upper valley. Rain chances over the
remainder of the CWA will be better predicated on the ample low
level Gulf moisture forecast, generally at or above two inches near
the coast, except for a brief decrement on Sunday. Should see a mix
of clouds and sun throughout, maybe leaning toward mostly cloudy,
with near normal temperatures.  Retained the inherited forecast with
minor changes, and used a model blend as the background. The GFS was
slightly wetter in a couple of the periods, but comparable to the
ECMWF in most other respects.

MARINE:
Now through Tuesday night: Minimal chance in the forecast for the
next 36 hours across the northwest Gulf as high pressure remains
well to the northeast, causing modest onshore east to southeast
flow. Wave action will remain consistent through tomorrow in the 2
to 3 foot range. An increase in fetch length later tomorrow will
bring some higher longer period swells closer to shore Tuesday
night. Streamer shower activity will continue tonight and again
tomorrow night, mainly just before dawn.

Wednesday through Saturday night: The pressure field will remain
rather broad and flat through the long term, supporting continued
light to moderate onshore winds and low to moderate seas. However,
winds will back from southeast to east Wednesday and Thursday as a
new air mass works into the area from the north. Subsequent high
pressure reinforcement will further back winds to northeast Thursday
night. Ample moisture pooling ahead of the associated weak front
identified to arrive Thursday night will keep at least a slight
chance of showers and thunderstorms in the forecast for the marine
areas.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...None.
&&

$$

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