Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 212321 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
621 PM CDT Sun Jul 21 2019

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

&&

.AVIATION...VFR expected to prevail through the period, though a
ceiling of cirrus clouds is likely much of the time, due to an
upper-level disturbance over the NW Gulf. Currently gusty SE winds
will subside around sunset. With a somewhat looser pressure
gradient in place on Monday, winds should be more moderate. Cannot
completely rule out a stray shower or thunderstorm along the sea-
breeze boundary Monday afternoon, but, with coverage expected to
be isolated, confidence is rather low on impacts at any specific
terminal.

&&

.PREV DISCUSSION... /issued 253 PM CDT Sun Jul 21 2019/

SHORT TERM (Tonight through Monday Night): The main mid level ridge
will retreat to over the Four Corners area tonight and Monday, with
a mid level low over the north central to northwest Gulf. The
feature is evident on satellite and is shedding high clouds toward
the lower Texas coast. Broad high pressure remains in control at the
surface. Overnight low temperatures will be 75 to 80 degrees with a
light southeast wind. With the H5 ridge temporarily to the west in
favor of deep troughing over the East, slightly lower heights will
prevail over the Gulf, though broad high pressure will continue at
the surface. Activity from the southwest Gulf may work up along the
coast to the local marine sections tonight through Monday morning,
bringing a few showers and thunderstorms. High res models suggest a
weak sea breeze Monday afternoon, and tongue of moisture supporting
an afternoon extension of sea breeze convection west across the
Ranchlands and Brush Country, but confidence is low to moderate with
that working out. High temps will be in the 90s and close to average
along the coast on Monday, but may get a few degrees above the
century mark out west, with associated heat index values of 105 to
110 degrees. Fair weather will prevail Monday night, with lows in
the mid 70s.

LONG TERM (Tuesday through Sunday): The long term begins with
mid-level ridging settling over the Four Corners region of the US
and a deep trough extending southwestward over the eastern third of
the country, allowing the much anticipated cold front to approach or
even pass through Deep South Texas and the Rio Grande Valley Tuesday
night into Wednesday morning. The primary impacts of this weak cold
front will be the potential rainfall with the influx of moisture,
the wind shift and the temperature drop to slightly below normal
values.

As far as rainfall potential goes, precipitable water values are
expected to exceed 2 inches Tuesday evening through Wednesday
morning. This influx of deep moisture along with the passing of the
front is expected to lead to rain shower and thunderstorm
development with rainfall totals up to half of an inch. Locally
heavier rainfall may be possible. While the temperature change is
not expected to be drastic with this front, temperatures are
expected to drop to slightly below normal values for this time of
year, bringing a much needed break from the extreme heat.

Models have come into better agreement with the timing of the
approach of the cold front, however they disagree on how far south
it progresses along with how it behaves later in the week. This
uncertainty decreases our confidence in the PoP forecast for
Wednesday through the weekend, but regardless, the lingering
moisture and lighter winds leave a favorable environment for sea
breeze convection to develop during this period, so will keep slight
chances for the coastal areas and offshore each day through the
week. To add to the uncertainty, despite the better model agreement
on the approach of this front, climatology has shown that it is
unusual for cold fronts to dig this far south in the month of July,
making this a tricky forecast overall.

Heading into the weekend, an inverted trough begins to develop over
the western Gulf and may lead to an increased chance for showers and
thunderstorms.

MARINE (Now through Monday night): Broad high pressure will support
light to moderate southeast winds and low to moderate seas the next
36 hours. Showers and a few thunderstorms may move up from the south
tonight through Monday.

Tuesday through Friday Night: Low pressure across the western Gulf
of Mexico allows the pressure gradient to weaken through most of the
long term period. A weak cold front Tuesday night into Wednesday may
increase winds and seas briefly, otherwise, generally favorable
marine conditions are expected through the rest of the week and
weekend. Small craft may need to exercise caution on the bay and
nearshore waters with the frontal passage on Wednesday.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...None.
&&

$$

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