Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 271716 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1216 PM CDT Thu Apr 27 2017

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

.AVIATION...Satellite images and surface observations indicate low
to middle level clouds across the southern and eastern portions of
the CWA early this afternoon. Ceilings were near 2200ft at KPIL to
near 3000ft at KHRL/KMFE. Visibilities were near 5SM with haze at
KEBG/KT65 to near 6SM with haze at KPIL. Expect MVFR conditions
through 21Z across the eastern half of deep south Texas before a
weak frontal boundary across the Rio Grande valley moves northward
as a warm front. VFR conditions will prevail across the CWA after
21Z through 03Z before low clouds develop late tonight as low
level moisture increases across the area. MVFR TO IFR conditions
will develop late tonight into early Fri morning as a result.

.PREV DISCUSSION... /issued 632 AM CDT Thu Apr 27 2017/
DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Cold front is draped across the Lower and Middle rio
Grande Valley with lower clouds moving southwest along front from
the Gulf of Mexico. MVFR ceilings around 1500-2500 feet are
expected for at least a few hours this morning in the KBRO and
KHRL vicinities with lower chances of the lower flight categories
reaching KMFE. As day time heating develops mixing out of the low
level moisture will allow for the stratus to break up with VFR
conditions through the afternoon. A developing low level jet and
strengthening surface inversion will allow for stratus to
redevelop this evening with high probabilities of widespread lower
MVFR cigs and even IFR ceilings developing for several hours
overnight especially near the coast. light northeast to east
winds today with exception to some stronger gusts along and east
of the coastline this morning. Stronger southeast to south winds
develop tonight with gusts of 20 to 25 knots. Even stronger south
winds (30-35 kt gusts) to impact KBRO and KHRL Friday.

PREV DISCUSSION... /issued 453 AM CDT Thu Apr 27 2017/

SHORT TERM (Now through Friday): A cold front that is currently
moving through Deep South Texas should weakly pass through the RGV
with a light-to-moderate northeast breeze and lowering dew
points. The front is expected to dissipate with winds quickly
veering east early this afternoon and southeast before sunset.
Temperatures this afternoon will be relatively cooler (10-15
degrees), than yesterdays scorcher due to the wind direction
change but still above end of April normals (approx. 5 degrees).
No rain with the front but we will see some increasing cloud
cover this morning as shallow layer of moisture pools in the
vicinity of the front.

Southerly winds return and increase tonight and Friday as a
developing storm system intensifies over the Southern Rockies. Low
level jet strengthens upwards of 40 knots in response to
deepening cyclogenesis across the Southern Plains. This will lead
to breezy conditions developing tonight and breezy to windy
conditions expected Friday. Strongest gradient will be between I-69E
and I-69C corridors, mainly the Lower RGV and possibly Eastern
Hidalgo, where a wind advisory may be needed. The southerly flow
and the warm elevated mix layer to combine to increase
temperatures well above normal once again with the hottest
readings expected over the west two-thirds of the CWA. Models
continues to push highs well above 100 degrees for a large area of
the mid and upper RGV as well as the Western and Northern Ranch

LONG TERM (Friday night through Wednesday night): 00Z runs of GFS
and ECMWF in rather good agreement overall through the middle part
of next week. Larger-scale flow will continue to feature a mean
trough over the central CONUS.

Friday night will be warm, muggy, and somewhat breezy along the
coastal counties as low pressure over the Southern Plains
interacts with higher pressure offshore of the SE CONUS. Models
indicating a 30-40KT low-level jet at H85.  Hot temperatures
continue for Saturday, with afternoon maxes generally 1-2F above
those on Friday. Flow becomes westerly between H7 and H85,
especially out west, allowing H85 temps to again soar to 25-28C.
Surface winds stay more southerly for eastern counties, so not
expecting a repeat of Wednesday`s 100+ degree readings in the
Brownsville area. Forecast/record highs for HRL and MFE are
99/101F and 101/102F, respectively, so both of those could be in
jeopardy. Winds will again be breezy, but appear to be a bit
weaker vs. Friday, so not thinking Wind Advisory criteria will be

A cold front moves through the CWA during the pre-dawn hours of
Sunday, which will bring some relief from the heat by knocking
afternoon temps back into the normal range of 86-89F for the mid-
Lower RGV, as well as transporting in much drier air. Dewpoints
tumble into the 30s and 40s by afternoon. Moisture along/ahead of
the front not very impressive, but models consistent in showing a
narrow window for isolated light showers to develop near the coast
prior to 12Z and through about 18Z offshore, so have reintroduced
some marginally mentionable PoP`s. As the drier air punches in
through the afternoon, Fire Weather concerns are likely,
especially over Starr/Jim Hogg/Zapata counties, as NNW winds
increase to over 15mph. Fuels are currently rated extremely dry
over the SE areas, so those areas will have to watched as well.

Surface high pressure settles over the area on Monday, then
gradually migrates eastward through Wednesday. Winds veer back to
SE, gradually increasing temps and humidity levels. Could be
enough low-level moisture in place by Tuesday night for some
"streamer" showers offshore and near the coast.

Long-range guidance brings next front into the area sometime later
Wednesday/early Thursday, with some decent rain chances suggested,
though most likely beyond the current official forecast period.

MARINE...Now through Friday:  Northeast winds are increasing behind
a cold front that is moving trough the coastal waters early this
morning. Much drier air north of the front is allowing for
mechanical mixing of stronger winds aloft to the water surface.
This mixing is expected to begin to weaken a few hours after
sunrise. In the meantime, Small Craft advisories have been issued
for the Laguna Madre and extended for the Offshore waters through
at least 10 am to account for the stronger winds and potentially
building seas. Weak high pressure moves over the NW Gulf this
afternoon with lighter east winds and subsiding seas. Southerly
winds increase tonight and Friday as an intensifying storm system
takes shape over NW Texas and Oklahoma. Winds are expected to
increase steadily overnight and strengthen Friday with another
round of small craft advisory conditions for all coastal waters.

Friday night through Monday night: Stretch of unfavorable marine
conditions primed to continue into early Monday. Sustained
strong SE winds around 20-22 knots persist across the coastal
waters Saturday, building seas to 8-10 feet. Small Craft
Advisories (SCA) are highly likely during this period. Winds
briefly relax ahead of a cold front late Saturday night, but seas
remain agitated enough to maintain SCA conditions. Strong
northerly winds last through much of the day Sunday, with seas
relaxing back toward Small Craft Exercise Caution levels by early
Monday. Winds and seas finally become more favorable, at moderate
levels, for Monday daytime.



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