Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 200349 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
949 PM CST Thu Jan 19 2017

.DISCUSSION...Surface observations and satellite images indicate
that fog and low clouds are developing across Deep South Texas
late this evening. Moist soils from recent rainfall, an inversion
just off the surface, and light winds should allow widespread fog
to develop overnight. Made a quick update to increase cloud cover
and for the mention of areas of fog across much of the area
overnight. Some locally dense fog is possible overnight but
increasing cloud cover should limit widespread dense fog. Also,
made some minor adjustments to the temp/dewpoint grids due to
observational trends. No other changes needed.

&&

.PREV DISCUSSION... /issued 607 PM CST Thu Jan 19 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Satellite images and surface observations continues to
show lingering low and high clouds across the eastern half of Deep
South Texas this evening. With moist soils from recent rainfall and an
inversion just off the surface, confidence is increasing for low
clouds to continue and possibly widespread fog overnight into
Friday. MVFR conditions will likely to continue this evening with
IFR/LIFR conditions developing after midnight and may possibly
drop to VLIFR at times through Friday morning. MVFR ceilings
expected through Friday afternoon with VFR ceilings possible at
MFE late in the period.

PREV DISCUSSION... /issued 323 PM CST Thu Jan 19 2017/

SHORT TERM (Tonight through Friday Night): A 500mb low pressure
system continues to move eastward across the Central Plains with
a trough axis passing through Deep South Texas this afternoon.
Visible satellite imagery indicates continued overcast skies east
of Highway 281 with widespread clearing behind the line.
Differential heating has led to temperatures nearing 80 degrees in
the Upper Valley and only mid 60s in the Lower Valley this
afternoon. Models are in general agreement that clearing will
continue from west to east this afternoon. Tonight, the main
concerns will be the possibility of fog developing after midnight,
especially along Highway 281 where rain fell last and this
morning. Model soundings continue to show a strong temperature
inversion with a moist layer near the surface and subsidence
moving in aloft. This, combined with light and variable winds
expected overnight, low clouds and patchy dense fog will be a good
possibility.

Friday, a shortwave impulse rotating around the trough may provide
one more chance of rain after 12Z, but there is some uncertainty due
to the lack of moisture available. Have kept POPs mainly to the
northern areas with and over the Gulf of Mexico. Temperatures will
warm up into the lower 80s along the Rio Grande with light S/SW
winds and less cloud cover expected Friday afternoon.

LONG TERM (Saturday through Wednesday): Will focus on Saturday and
Sunday for significant weather in the long term. Light, downsloping
west winds will maintain a dry air flow across the area, resulting
in very warm weather with high temperatures nearing record values on
Saturday. Hedging slightly above a model blend, forecast high temp.
values of 87/88/89 for BRO/HRL/MFE, respectively, will bump up
against record highs of 90/87/91.

A deep, southern high plains storm system moving across the Texas
panhandle and Oklahoma Saturday night into Sunday, and then dipping
into the ArkLaTex area, will trail a dry cold front that will impact
the RGV and deep South Texas on Sun. Northwest winds will increase
Sat night after midnight, likely reaching wind advisory criteria by
mid Sunday morning for virtually all of the CWA, lasting through the
day.

Monday and Tuesday will be fairly nice weather days, resuming a
warming trend with 70s on Monday and 80s on Tuesday. Another high
plains storm system will deepen on Tuesday, with a cP air mass
moving in behind, and under an elongated mid level trough over
the southwest. That`ll push a front through on Wednesday, only to
be reinforced on Thursday, with only slight rain chances over the
Gulf however. High temps will cool into the 70s on Wednesday and
60s on Thursday.

MARINE:

Tonight through Friday Night: Light and variable winds will
continue across the marine areas overnight tonight with seas
ranging from 2 to 3 feet in the Gulf waters. Winds will increase
out of the south Friday afternoon and evening as a storm system
develops in the Central Plains. A mid- level impulse moving
overhead on Friday may produce a few isolated showers over the
Gulf.

Saturday through Tuesday night: Light to moderate southeast to
south winds and low to moderate seas will prevail Saturday through
early Sunday morning when a cold front will bring strong
northwest winds to the marine areas. Small craft advisory
conditions will develop over the Gulf Waters a few hours before
dawn, followed by the Laguna Madre, with sustained gale force
northwest winds possible across the offshore waters by mid
morning. Concurrently, gale force gusts will be possible across
the nearshore. The Laguna will probably stay subgale, but will not
rule out an occasional gust to gale force. Wave heights offshore
may build to 12 feet Sunday. Winds will begin to diminish after
sundown Sunday, dropping below advisory criteria for the Laguna
Madre by late evening and for the Gulf waters overnight, though
wave heights will lag behind, with heights enough to sustain
advisory conditions across portions of the Gulf through Monday
morning.

FIRE WEATHER...Red flag conditions may develop Sunday behind a
strong, dry front moving through the area. A fire weather watch has
been issued. Fuels will have a day of sunshine and dry, downslope
flow to maintain lower relative humidity values on Saturday, further
curing fuels. That, combined with relative humidity values
decreasing into the teens for the western two-thirds of the CWA on
Sunday, along with robust northwest winds, including 20 ft winds
above 15 mph from midmorning through the day, will produce critical
fire weather conditions.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  62  84  65  83 /  10  10  10  10
BROWNSVILLE          63  85  65  87 /  10  10  10  10
HARLINGEN            60  83  64  88 /  10  10  10  10
MCALLEN              62  85  63  89 /  10  10  10   0
RIO GRANDE CITY      61  85  59  89 /   0  10  10   0
SOUTH PADRE ISLAND   65  80  66  78 /  10  10  20  10

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...Fire Weather Watch from Sunday morning through Sunday afternoon
     for TXZ248>257.

GM...None.
&&

$$

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