Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 261549 AAB

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
1049 AM CDT Mon Sep 26 2016

.DISCUSSION...Based on current trends, location and forecast of
the `oozing` wind shift/front have made wholesale changes to the
forecast today and a few tweaks to tonight. Will take a more
detailed look between noon and 1 pm to get a better handle on how
afternoon convection may evolve across the eastern third of the
forecast area (east of US 281/IH 69C).

Overnight convection and residue worked over the atmosphere from
Starr/Jim Hogg through Zapata County, and low ceiling, north wind,
and temperatures still in the lower 70s may be a signal for a
relatively cool afternoon with nothing more than occasional light
rain. Farther east, abundant mid and high clouds are trying to
erode, and winds are still more easterly than northerly so
potential remains for some convective development and potential
clustering. That said, lack of forcing aloft is critical to any
organized convection as 500 mb ridge core holds tough.

So, for the update: removed thunder mention for the remainder of
the morning and early afternoon, and worded as "scattered showers
with a chance of a thunderstorm" everywhere through mid afternoon
with similar wording right through sunset across the ranchlands.
Lowered high temperatures just a hair east of US 281/IH 69C but by
3 to 5 degrees farther west, particularly along the SR 285/SR 16
corridor from Hebbronville to Zapata where breaks may not show up
and temperatures could hold in the mid to upper 70s.

Will take a closer look for Tuesday during the afternoon package,
but heavy rain looks like a non-starter with north/northeast flow
expanding deeper in the lower column and northwest flow arriving
in the mid/upper part of the column.


.PREV DISCUSSION... /issued 618 AM CDT Mon Sep 26 2016/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Scattered showers and thunderstorms continue to
spread northward across the region. A thunderstorm is approaching
KMFE currently and will bring tempo vis and cig reductions through
the next hour. Tempo TSRA continues today for the region. Some
lower chances for rain are possible overnight tonight, but another
round of thunderstorms forecast for Tuesday.

PREV DISCUSSION... /issued 404 AM CDT Mon Sep 26 2016/

SHORT TERM (Today through Tuesday): Complicated forecast in store
today as moisture surge continues into south Texas. H5 trough has
completed it split, with the main trough sweeping east across the
Great Lakes, and the cutoff low dropping into NW Mexico. Cold front
associated more with the northern trough continues to drop southward
through central Texas. Moisture already in place locally, as noted
by evening sounding. Shower that passed over KBRO recently dropped
0.25 inches in 15 minutes, so thunderstorms are efficient rain
producers. Rain forecast is split, with western valley seeing better
chances this morning from earlier storms, but tapering off later
this morning. Lower valley thunderstorms already starting to
increase in coverage, but are remaining scattered in nature, so
local atmosphere won`t stabilize quite as rapidly, so showers will
continue into the afternoon during peak heating. QPF amounts will
remain half to one inch, mainly limited by showery nature of
precipitation. As the front sweeps in from the north overnight
tonight, drier air will entrain into the northern counties, allowing
rain chances to decrease considerably. The front will likely hang up
along the coast or morph more into a weak coastal trough. This will
continue to focus rain chances along the immediate coast through the
night and into the day Tuesday.

LONG TERM (Tuesday Night through Sunday): Low to mid level
moisture will remain relatively high across northeast Mexico and
the western Gulf of Mexico Tuesday but will gradually diminish
across the CWA Tues night into Wednesday as the 500mb trough
deepening across the eastern United States and the 500mb ridge
building across the west central U.S. brings drier air southward
across east Texas. The drier air should make its way southward
into deep south TX Wed night into Thursday. Rain chances will
diminish Tues night into Wednesday and not much in the way of rain
chances is expected through the rest of the forecast period as the
500mb ridge across northern Mexico and west Texas continues to
provide subsidence across south TX through the rest of the week.

Today through Tuesday...Winds have begun to shift more to the
northeast in response to the approaching cold front. Wind speeds
remain modest, except during the passage of any showers, which have
pushed winds up to right around 20 knots. Northeast winds will begin
to increase seas to near 4 feet, being limited by the short
northeast fetch over shallower waters. Shower activity will be on
the increase today as the cold front moves into the northwest Gulf.

Tuesday night through Friday...Light to moderate northeast winds
will prevail across the coastal waters Tuesday night into
Wednesday with surface high pressure across Texas and weak surface
low pressure across the Bay of Campeche. The pressure gradient
will remain weak across the lower Texas coast Thursday. Light
to moderate northeast winds will prevail across the western Gulf
of Mexico Thursday and Friday with surface high pressure building
southward across the central United States.


BAYVIEW/PORT ISABEL  87  75  86  76 /  50  40  50  30
BROWNSVILLE          88  74  87  75 /  50  50  50  30
HARLINGEN            88  73  86  74 /  50  40  50  30
MCALLEN              90  74  88  73 /  60  50  50  30
RIO GRANDE CITY      88  71  85  71 /  70  50  40  30
SOUTH PADRE ISLAND   85  78  83  78 /  50  40  50  30




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