Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 232100

Area Forecast Discussion
National Weather Service Brownsville TX
300 PM CST Tue Jan 23 2018

.SHORT TERM (Tonight through Wednesday Night):
IR Satl imagery shows high and mid level cld cover advecting over
the RGV today with a light to moderate NE surface flow
prevailing. The 12Z BRO sounding shows that the atms over the
region is pretty dry with the exception of the 700-850 mb layer
which shows a narrow band of some better moisture values. The
deeper layer moisture will start increasing over the RGV from the
south as a 500 mb closed low approaches the region from the west
tonight through Wed Night. Sct pockets of 500 mb vorticity will
rotate around the base of the trough axis moving across the RGV.
The passage of these vort maxes will maintain the threat of
isold/sct rain showers over mainly the southern tip of TX and
across the offshore waters through Wed Night.

The light NE low level flow will combine with the increasing cld
cover and pops to allow for temps to remain on the mild side
throughout the short term. Short Term model temps are in pretty good
agreement and will go close to a three way blend for highs and lows
through tomorrow night. Short Term model pop trends are a little bit
trickier with the GFS and ECMWF showing better agreement on lower
pops through tomorrow night with the NAM coming in the wettest. Will
go with a blend of the GFS and ECMWF since the NAM seems to be the
odd model out.

Overall confidence in the short term forecast wording is above

.LONG TERM (Thursday through Tuesday):
Starting Thursday, the cutoff low over NW Mexico begins to weaken
and eject to the northeast. This will continue to draw midlevel
vorts across south Texas, and slowly effect areas further north as
the day progresses. The continued instability will continue the
chance for rain Thursday, expanding north through the day. As the
main wave passes by sunrise Friday, flow aloft will be more
westerly, limiting any precipitation to surface based streamers
during the day Friday. Limited moisture will keep chances to
isolated at best. Saturday the next longwave trough will be
progressing across the central US, drawing another round of colder
air southward along the eastern slopes of the Rockies. The leading
edge cold front will sweep across Texas Saturday, and should be
near or through the valley by Saturday night at midnight. Models
are differing on the timing of the passage of the upper trough, so
the timing of the northwesterly drying flow will be sometime
Monday or Monday night.


Now through Wednesday Night: The light NE low level flow over the
Bay and Gulf waters will continue throughout the short term
period maintaining pretty quiet marine conditions. Expect marine
winds and seas to remain below SCA levels through Wed Night or
both the lower TX Bay and Gulf waters.

Thursday through Sunday: High pressure across the East Coast will
be interacting with developing low pressure dropping in from
central Canada to cause southeast winds across the northwest
Gulf. Wind speed will remain modest in the 10 to 15 knot range,
but it will be enough to keep seas agitated above 4 feet. North
winds return Saturday morning as the next cold front sweeps across
the region. The airmass behind the front is not especially cold,
and doesn`t have considerable southward momentum, so winds are
currently not expected to reach 20 knots after passage. Northerly
winds will be able to further agitate seas, with swells of 5 to 7
feet expected Saturday and Saturday night. The front has potential
to spark scattered showers as it passes on Saturday, which may be
accompanied by locally gusty winds. Breezy north winds will
continue through most of the day Sunday as well.


BAYVIEW/PORT ISABEL  52  63  51  64 /  40  40  20  40
BROWNSVILLE          52  65  51  65 /  40  50  30  30
HARLINGEN            50  66  49  64 /  30  30  20  40
MCALLEN              51  67  50  64 /  20  20  10  40
RIO GRANDE CITY      48  66  47  64 /  10  10   0  30
SOUTH PADRE ISLAND   54  62  54  62 /  40  40  20  30




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