Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 141737 AAB

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
1137 AM CST Sat Jan 14 2017

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


.AVIATION...More widespread cloud cover continues to develop
across the area, with light showers moving northwestward into the
region. TEMPO groups have been extended for KMFE for impending
rainfall. Light showers may continue into the evening, but will
have lesser effects on local airports after sunset. Ceilings are
forecast to fall to around 1500 overnight, but fog formation is
not expected toward sunrise. Winds will remain from the southeast
today 15 to 20 knots before decreasing to 5 to 10 overnight.


.PREV DISCUSSION... /issued 558 AM CST Sat Jan 14 2017/

DISCUSSION...Updated for latest /12Z/ aviation discussion below.

AVIATION...Only a few cosmetic changes to the prior forecast.
First...the tricky cloud and fog forecast for a few hours this
morning. Brownsville/SPI, a known low spot, has seen
light/variable winds and visibility bouncing between 1/2 and 4
miles in radiation fog with generally clear skies above (though
ASOS is sometimes seeing the fog as ceiling as well). Harlingen
recently cleared out but winds still at 7 knots which should keep
any mist (BR) in the MVFR range. McAllen was seeing a mid deck
passing overhead at forecast time which should kill off any fog
potential, though can`t rule out an MVFR ceiling which is most
likely soon after sunrise.

Thereafter, the only other change was to add a PROB30 group for
mid to late afternoon at Brownsville and Harlingen, per continued
trend of GFS with the aforementioned plume of moisture nosing up
through sunset, associated with a weak but noticeable shear axis
about 20 miles of so east of the shoreline. Don`t think it will
amount to much but could be enough to wet the ground and reduce
visibility to MVFR (4 or 5 miles) briefly.

After sunset, the moisture plume eases away from the coast, and
current forecast trends continue for ceilings to form up in
slightly stronger south-southeast flow toward daybreak which
should help pool moisture below weak inversion. For now, based on
persistence in model soundings with the 06Z run, dipped ceilings
to low MVFR at Brownsville and McAllen and IFR at Harlingen.

PREV DISCUSSION... /issued 357 AM CST Sat Jan 14 2017/

SHORT TERM (Now through Sunday): A "spring" in our step across Deep
South Texas and the Rio Grande Valley for the weekend with continued
warm and relatively humid for the heart of what is our coldest part
of the calendar year, on average.  Temperatures on the whole will
continue nearly 20 degrees above average for the morning wake-up
and a good 10 to 12 degrees above for the afternoon, which will
continue pushing the monthly average up to between 5 and 7 degrees
as we pass the middle of January.

As for the sensible weather...a pocket of moisture up through 700 mb
passes through the Lower Valley and off the coast this afternoon
courtesy of a weak and tight shear axis sliding from east of
Tamaulipas northward along the Lower Texas coast before weakening
over/east of the Lower Texas Gulf waters this evening. Combined with
daytime heating and slightly lower southeast winds than the more
robust Valley wind machine, would not be surprised to see quick
hitting passing showers mainly east of McAllen this afternoon,
perhaps including the beaches. Before any rain and cloudier skies
arrive, any early morning low clouds should lift/dissipate by mid
morning through early afternoon, allowing temperatures to reach
their forecast highs in the low to mid 80s for the Valley and ~80
for the ranchlands.  These values are a few degrees above all but
the ECMWF guidance and in line with trends which continue to
favor warmer temperatures than statistical guidance indicates.

Tonight looks to be a repeat of Friday night/early this morning,
with the only slight difference veering winds in the low level jet
region (850-925 mb) to the south and increasing a few ticks over
this morning.  Low level moisture is a bit thicker but without any
vertical motion expect little more than low clouds.  Surface winds
will hold up close to 10-12 mph in most areas, perhaps higher across
the Rio Grande Plains as we`ve seen this morning, which should
preclude any fog development.

On Sunday, the Valley Wind Machine gets a boost with strengthening
southerlies as still-vigorous 500 mb wave lifts into west Texas with
~1000 mb surface low just behind in southeast New Mexico.  The
southerlies transport moisture into the system but well north of the
Valley, and mid level westerlies help thicken the very dry column
down to 700 mb with drying in southwest flow down to 850 mb by late
afternoon. This should break up any morning overcast into partly
sunny skies especially for the Valley through the Rio Grande Plains.
Winds may get close to advisory levels (30 mph sustained with gusts
to 40 mph) and will have to monitor closely over the next 24 hours
but for now have sustained 25 with gusts 30 to 35 mph for the Valley
and slightly less farther north and west...the classic windy spring
type weather we`re pretty used to here.

Across the northern ranchland areas, especially along SR 285, some
spotty showers may end the night and begin the morning but impact
should be minimal as area is closest to the slightly deeper moisture
from the South Texas Brush country toward the Big Bend region.

LONG TERM (Sunday Night through Friday): The most unsettled
period of weather during the long term portion of the forecast is
progged to occur Thursday and Thursday night as a tandem 500 mb
trough and surface cold front sweep through the Lone Star State
and produce scattered and showers for Deep South Texas and the Rio
Grande Valley. Otherwise, periods of isolated precipitation will
dominate with well above normal temperatures the rule.

MARINE (Now through Sunday): The better fishing/boating day will be
today (Saturday) as morning winds in Laguna Madre and out to 20 nm
should remain tolerable...15 knots or less...but somewhat more
difficult conditions are expected beyond 20 nm out as the day
progresses. Long fetch of east-southeast flow has already pushed
near 7 foot seas to buoy 42002 220 miles east of South Padre, and
expect elevated levels perhaps reaching 6 feet by late
morning/afternoon to require some caution for small craft due to

Similar conditions prevail tonight before Sunday sees the marine-
layer influenced lower values in the zero-20 nm waters with higher
winds/seas beyond 20 nm and also in the shallower Laguna Madre.
Caution levels at a minimum for both wind and seas in these areas a
good bet for Sunday late morning/afternoon...and advisories may be
needed especially for the west side of Laguna Madre.

Sunday Night through Friday: The most adverse marine conditions
during the period are forecast for Sunday night and Monday as an
enhanced pressure gradient produces Small Craft Advisory winds
and/or seas. Afterwards, generally more moderate winds and seas
are anticipated with the passage of a cold front late Thursday
possibly briefly creating adverse marine conditions at that time.

CLIMATE: If you`re wondering about records, there are a few
opportunities today and tomorrow to reach or exceed record afternoon
maximum temperatures.  Here are the records for the three primary
observing locations across the Valley as well as the forecast
through Sunday.

Location       Saturday Record  Forecast  Sunday Record  Forecast
Brownsville     88 (in 1887)       83        83 (2016)      83
Harlingen/coop  87 (in 1960)       84        86 (2016)      84
McAllen/Miller  85 (in 1980)       86        86 (2016)      86

Of interest is the Sunday records from 2016...and how 2017 may be a carbon




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