Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 201143 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
643 AM CDT Thu Apr 20 2017

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


.AVIATION...Little change to the forecast philosophy this morning.
One thing that developed since around 4 AM is the oft-seen band
of low MVFR to IFR ceilings from the mid Valley (KMFE) through
the South Texas Brush Country (IFR ceilings are mainly in Jim Hogg
County based on beefiness of infrared satellite loops). If
history is any guide these clouds will hang tough for a couple of
hours before lifting. By 15Z expect more scattered than broken low
VFR skies so went this direction without a TEMPO group in McAllen.
Elsewhere, skies are mainly clear and expect a more standard
development of mainly scattered VFR level clouds by 10 AM or so.

Remainder of forecast through 06Z/Thursday largely untouched. As
alluded to in earlier discussion, expect more widespread low MVFR
ceilings to develop between 1 and 4 AM, as indicated nicely in GFS
cross sections and model soundings as well as guidance from
NAM/GFS as well. ECMWF a bit less bullish on the low level
moisture but analog cases in southeast flow in spring match up


.PREV DISCUSSION... /issued 337 AM CDT Thu Apr 20 2017/

SHORT TERM (Now through Friday): For those with outdoor plans by
the pool, beach, or boat, the next two days are for you. With
weak 500 mb trough having exited/dissolved over the western Gulf,
the eastern edge of 500 mb trough takes charge. This maintains
surface high from the southeast U.S. westward into southeast Texas
today through Friday, with a slight increase in afternoon
southeasterly winds each day as well as some increase in surface
humidity overnight into Friday particularly near the coast.

Otherwise, the main story will be temperatures heating up into May-
like levels each afternoon with 88 to 94 from east to west (Valley)
today and 91 to 97 east to west (Valley) Friday, with temperatures
just a hair lower across the South Texas Brush Country.  Plenty of
sunshine today with fair weather cumulus rising with the mixing
height.  A clear start to the overnight but GFS/NAM indicating
broken to overcast low clouds after midnight for most areas as
southeast flow stays up a bit over recent nights.  Temperatures may
reach minimums around midnight and hold steady thereafter, with most
of the Valley beginning Friday in the lower 70s.  Those clouds will
lift and dissipate by late morning with mostly sunny skies through
scattered fair weather cumulus by early afternoon.

May see a little more haze and slightly lower air quality Friday
with northerly flow above 700 mb and south/southeast flow below
allowing more influx of agricultural soot/smoke to edge back across
the region. Doesn`t look all that bad compared with past spring
events, and with very dry air aloft mixing in a times conditions
should be kept in check...close to the low end of the moderate
category.  Check all your air quality data and forecasts at

For beachgoers: Though southeast winds pick up a little each day on
land, marine layer and relative low speeds (10-15 knots in the mixed
layer above it) should keep longshore currents at a dull roar and
surf waves around 2 feet...near perfect for late April.

LONG TERM (Friday Night through Wednesday): 500mb ridge across
northern Mexico and south Texas Friday will continue to provide
subsidence across the CWA Fri night into Saturday before a cold
front moves through the Rio Grande valley late Sat afternoon/early
Sat evening. Some moisture is expected to pool along and ahead of
the front providing a slight chance of showers and thunderstorms
Sat afternoon. Rain chances will increase Sat night even though
convection will be elevated in the wake of the front. Drier and
cooler air will filter into south TX Sunday with high pressure
building across the area in the wake of the front. Above normal
temperatures Saturday will be below normal Sunday before returning
to near normal Monday as the surface ridge across the state moves
eastward. Above normal temperatures will return by Tuesday as a
southerly flow develops next week with low pressure across
northwest TX. A weak 500mb shortwave trough is progged to move
across northeast Mexico and southwest TX by the end of the
forecast period and this will provide a slight chance of showers
and thunderstorms across portions of the CWA Wednesday.

MARINE (Now through Friday): Surface high pressure
stretched across the northern Gulf will continue to direct
southeasterly flow across the northwest Gulf. Gradient between ridge
and low pressure in the Texas Panhandle remains fairly weak, so
winds will remain in the 10 to 15 knot range throughout over the
Gulf with the typical diurnal trends...closer to 10-12 knots by day
and 12 to 16 knots overnight.  The Laguna Madre will flip that
script.  Modest swell will keep seas at 3 feet today and tonight but
values could rise a bit toward daybreak Friday especially offshore
where slightly stronger overnight winds will be. With thunderstorm
threat out of the way boating/fishing conditions should be
fine...don`t forget the sunblock!

Friday night through Monday...Moderate to strong southeast winds
will prevail across the coastal waters Fri night as a cold front
moves into central Texas. Winds will diminish Saturday as the
pressure gradient weakens across the lower Texas coast ahead of
the front. Light southeast winds Saturday will shift to the north
and increase Sat night as the front moves through the coastal
waters late Sat afternoon/early Sat evening. Strong northeast
winds will prevail across the coastal waters Sat night and the
pressure gradient will remain strong across the western Gulf of
Mexico Sunday. Winds and seas should diminish Sun night as high
pressure settles across the state. Moderate to strong north winds
Sunday will become light and variable Monday as the surface ridge
moves across the western Gulf. Small craft advisories will likely
be needed for the offshore waters Fri night and for all of the
coastal waters Sat night. Winds and seas will remain high offshore
the lower TX coast Sunday and small craft advisories will likely
continue for the offshore waters Sunday.




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