Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 240539 AAB

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
1239 AM CDT Mon Oct 24 2016

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


.AVIATION...Multi-layered clouds continue to stream across Deep
South Texas as mid to upper level disturbance passes over Texas
tonight into Monday. Expecting VFR conditions with cigs as low as
3500-5000feet at times through the overnight and early morning
period with a more substantial 5k feet deck developing by late
morning early afternoon as a weak surface inversion develops. As
the disturbance moves off to the east late today and tonight
clouds will begin to break up with more scattered conditions
becoming predominate. Light east-southeast winds to prevail
tonight and Monday.


.PREV DISCUSSION... /issued 651 PM CDT Sun Oct 23 2016/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...A multi-layer cloud deck and light southeast winds
prevail across Deep South Texas this evening. VFR conditions
expected to continue for the next 24 hours, but can not rule out
some brief field fog near HRL. A weak upper level disturbance
moving overhead tonight will keep clouds coming from time to
time. Southeast winds will become moderate Monday afternoon.

PREV DISCUSSION... /issued 256 PM CDT Sun Oct 23 2016/

SHORT TERM (Now through Monday Night): Very few "big picture"
changes were made to the current forecast this period, as
models/trends continued to lean toward a drier (rain-free)
forecast through the period.

The main reason is related to the stubborn 500 mb ridge.  Even
though the axis has edged into the western Gulf, the well
advertised weak disturbance is lifting well north of the Rio
Grande Valley today and tonight. Though the disturbance puts a
minor "dent" into the ridge, its westward extent keeps deep dry
air across the region through Monday with a more typical slight
increase along the Sierra Madre perhaps reaching into Zapata
County on Monday. By late Monday night, GFS shows a slight
increase in moisture up to 850 mb over the Gulf waters, but the
dry tongue between 850-700 mb holds very tough and should be
enough at this time of year to preclude anything more than silent
10 percent chances...and those would be across the Gulf only.

While the deep layers have significant dry pockets, there are still
notable layers of moisture today and tonight.  A batch of
clouds at 5-10 thousand feet...perhaps associated with the
aforementioned short wave...has left a mostly cloudy afternoon for
most of the Valley.  This batch should pass by evening but should
still see fairly thick cirrus into the evening with perhaps periods
of 4-6 thousand feet decks from time to time overnight. Monday looks
to be the proverbial "mix of clouds and sunshine" with more sunshine
as the afternoon wears on particularly across the mid/upper Valley
and ranchlands. Monday night looks to see mostly clear skies in
these same areas, with perhaps some return of cu/stratocu closer to
the coast but just how far inland remains in question.

The amount of clouds and clear will help dictate temperature trends.
Today, despite a "mostly cloudy" afternoon, McAllen is headed toward
90...a couple of ticks above the forecast.  With more sunshine and a
still warm atmosphere went above guidance in most areas by a degree
or two for Monday.  Passing clouds and periods of broken skies
tonight along with the gradual but not too crazy dewpoint recovery
should insulate things tonight...and current forecast range of 67 to
72 looks on target.  For Monday night, idea of clearer skies
combined with the longer nights gives credence to patchy fog late
across the ranchlands and rural RGV, so added an area but kept most
of the population out.  Though tricky near the coast, overall sense
of night and long period of calm winds should bring temperatures to
just a hair above seasonal levels for October 25, 63 to 68 in

LONG TERM (Tuesday through Sunday): 500mb ridge across northwest
Mexico and the southwest United States Tuesday and Wednesday
should provide northerly winds aloft across the CWA and surface
high pressure across the eastern U.S. will provide an onshore flow
through Wednesday. Moisture is progged to increase across the
coastal sections and this will provide a slight chance of showers
along the coastal waters and along the lower Texas coast through
Wednesday. The upper level ridge is expected to shift eastward
through the rest of the week but a slight chance of rain will
continue through Friday as moisture increases across the southern
half of the Gulf and northerly flow aloft veers to the east. Drier
air is progged to move across south TX and the western Gulf of
Mexico through the rest of the forecast period.

MARINE (Now through Monday Night): Relaxed winds and seas keep
things copacetic through Monday as broad high pressure covers the
Gulf and southeast U.S. states. A stronger high begins building
across the Ohio Valley and into the eastern U.S. Monday night
which will help pick up the easterly gradient from the central
Gulf to the Florida Sun coast. A bit hard to figure exactly when
some of the swells will arrive, but for now kept/nudged seas up to
4 feet in the outer waters by late Monday night. Wind will remain
below 15 knots through the period.

Tuesday through Friday...Light east to southeast winds will
prevail across the coastal waters Tuesday with surface high
pressure across the eastern United States. The pressure gradient
is expected to remain weak across the western Gulf of Mexico
Wednesday and Thursday but a fetch of easterly winds across the
northern Gulf will likely provide swells that move westward
towards the Texas coast. In addition...winds are progged to back
to the northeast across the lower TX coast Thursday and light
northeast to east winds will likely prevail through the rest of
the week but seas should continue to gradually build offshore the
lower TX coast with the persistent swells from the east.


BAYVIEW/PORT ISABEL  69  86  71  85 /  10  20  20  20
BROWNSVILLE          68  89  70  87 /  10  20  20  20
HARLINGEN            67  90  67  88 /  10  20  10  20
MCALLEN              69  93  70  90 /  10  10  10  20
RIO GRANDE CITY      67  89  66  89 /  10   0  10  10
SOUTH PADRE ISLAND   74  83  78  82 /  10  20  20  20




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