Area Forecast Discussion
Issued by NWS Brownsville, TX
FXUS64 KBRO 282326 AAA
Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
526 PM CST Mon Nov 28 2016
.DISCUSSION...Updated for latest aviation discussion below.
.AVIATION...Below average confidence still for dense fog at the
TAF sites, though MVFR after midnight and tempo IFR look pretty
good and were included in the TAFs. A frontal boundary is moving
into the Ranchlands and Brush Country with lower dew points, but
the HRRR for example doesn`t quite bring it through.
.PREV DISCUSSION... /issued 253 PM CST Mon Nov 28 2016/
SHORT TERM (Tonight through Tuesday Night):
Base of upper trough moving
across NC Texas with the strong LLJ getting shunted eastward. This
shows up nicely on local doppler radar with veering winds gradually
spreading west to east through the morning. The associated cold
front, moving through the Hill country and into SC Texas, is
expected to slow down and pull up stationary over the CWA later
tonight. This will set the stage for fog development after midnight
as light SE winds usher in very shallow but high dew point air.
Models are a bit indifferent if there will be a low stratus deck or
the potential of dense fog. The favored areas will be across the Mid
and Lower Valley in the vicinity of the anticipated stalled front.
Models also show the worse conditions around and shortly after
sunrise when saturation reaches its peak. Confidence is slight below
average to issued a dense fog advisory at this time with model
uncertainty. With the front passing through approximately half of
the CWA temperatures will cooler across the NW Zones with another
much above normal night in the SE half.
The next upstream shortwave tracks across Texas later Tuesday with a
stronger cold front moving through the CWA Tuesday night. A non
eventful day is on tap with mostly cloudy to cloudy skies in the
morning with partial clearing in the east later in the afternoon as
low level moisture is shown to increase. the front is not expected
to bring rain with depth of the moisture remain below 850mb.
However, some streamer showers may develop over the Coastal waters
tomorrow night with a few possibly moving into the Lower Valley.
Otherwise, another warm day is in store with temperatures ranging in
the mid 80 to upper 80s and a few locals reaching 90 degrees in the
Mid Valley if the sun breaks out in time.
LONG TERM (Wednesday through Monday):
Beginning of the long term starts with the passage of the finale
of the cold front passage Wednesday morning. Still looks like
precipitation will be limited to mainly offshore waters. Dry air
sweeps in fairly quickly during the afternoon, so skies should be
nearly clear by sunset. This will provide for good radiational
cooling Wednesday night, with lows either side of 50 degrees. Weak
onshore flow returns on Thursday, slowly building cloud cover from
the coast inland.
The weekend forecast is still muddled by a considerable upper low
dropping into northwest Mexico. Most models are fairly consistent
with the low stalling across northwest Mexico most of the weekend,
with hints that it finally ejects starting Monday. This setup will
induce coastal troughing just offshore from south Texas for the
weekend, which produces a good overrunning pattern. Friday and
Saturday, all models are in good agreement on widespread
light rainfall for the region. Now the outlier model is the EC,
which depicts the cutoff low not really cutting off and quickly
jumping into the central US by Sunday. This would bring the
moisture to an end early and leave a drier Sunday and Monday. As
this seems to be the outlier of the remaining models, have opted
to discount the EC model, in favor of a blend of the remaining
models, which keep moisture and rainfall in the region through
Monday. With this in mind, have pushed PoP chances back up to low
end likely through Monday, before tapering off for Tuesday as the
cutoff low finally ends.
Now through Tuesday Night: South winds and the high seas will
continue to lower tonight as a cold front approaches the coastal
bend but residual higher seas may linger until between 9 pm and
midnight maintaining SCA`s offshore. the front pulls up stationary
and will be waiting for a reinforcing high pressure to push it
through around late Tuesday night or by sunrise Wednesday. In
advance of the wind shift expect a moderate southeast flow with a
moderate sea maybe high enough to warrant exercise caution
conditions. Small craft advisories are likely to be issued for the
early Wednesday cold front passage.
Wednesday through Friday: Winds behind the front Wednesday morning
will jump quickly to 20 to 25 knots, while seas jump to 8 to 10
feet with higher swells late in the afternoon. Conditions will
relax fairly quickly Wednesday night with onshore flow returning
Thursday morning. The coastal trough will develop by Friday
morning, with agitated conditions forecast through much of the
weekend. Seas will jump up to 9 to 12 feet for the weekend, with
winds onshore of 20 to 25 knots.
GM...Small Craft Advisory until midnight CST tonight for GMZ170-175.
Small Craft Advisory until 9 PM CST this evening for GMZ150-155.
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