Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 190606

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
106 AM CDT Sun Mar 19 2017

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


.AVIATION...IR satellite imagery shows low clouds and patchy fog
developing across the Mid Valley and Ranchlands. Have generally
kept TAFs the same as previous forecasts with MVFR to IFR cigs
still expected to develop through the early morning hours...along
with some MVFR visbys for fog. Dry air aloft will mix down today
with clouds lifting to VFR levels. Meanwhile...SE winds will
continue across the region with some occasionally higher gusts


.PREV DISCUSSION... /issued 647 PM CDT Sat Mar 18 2017/

DISCUSSION...Made a few tweaks to inherited forecast to sky cover
and wind basically to improve (lower) speeds along the beach which
is still packed with seasonal visitors and given classic marine
layer setup and lighter low level (i.e. 925 to 850 mb) speeds is
seeing more comfortable winds by day (8 to 12 mph) than just 5 to
15 miles inland (15 to 25 mph). That was situation today and will
likely be scenario Sunday as low level wind fields remain modest.
Beach wind speeds may tick up a hair Sunday with better mixing of
drier air but will still be 10 mph lower on average than inland

AVIATION...Current forecast is pretty much on target and made
little changes through 18Z Sunday. Latest (18Z Saturday run) model
soundings still show potential for a brief period of IFR ceilings
in the mid Valley (McAllen/Miller) between 08Z and 13Z and
maintained this idea with a prevailing broken MVFR ceiling
otherwise. Closer to the coast, a similar situation to early this
morning is likely with passing or developing MVFR ceilings amidst
otherwise SKC to FEW conditions. As for Sunday, while there may be
a period of BKN MVFR conditions through late morning, deeper drier
air is arriving below broad upper ridge and elected to roll
prevailing SCT conditions with a brief period of TEMPO BKN low
VFR. The afternoon may well go clear at all terminals, but kept
FEW to be honest with smidges of moisture at the raising cloud
level. As for winds, just a few ticks off of this afternoon`s
fresh but not crazy speeds as the Valley Wind Machine eases
off...for a day, anyway.

PREV DISCUSSION... /issued 242 PM CDT Sat Mar 18 2017/

SHORT TERM (Now through Sunday night): Little change to the
weather will occur during the next 36 hours, as upper-level
ridging remains parked over Texas with a surface high over the
north-central Gulf of Mexico. Temperatures will continue to run
5-8 deg F above normal for both afternoon highs and morning lows.
Winds will remain from the SE, lighter at night and more moderate
in speed during the afternoon but still less than 15 mph.
Dewpoints currently in the mid-60s for the Mid- Lower Valley will
be in the upper 50s to lower 60s by mid- afternoon on Sunday, as a
slug of drier (yet) air aloft moves in and mixes down during the
afternoon. This will also yield lots of sunshine for tomorrow,
with a less widespread Cu field expected vs. today. Also expecting
patchy fog to form after midnight tonight for favored interior
areas. Do not expect it to become dense, though, as prog soundings
not showing a low enough or strong enough inversion to really
confine the moisture at the surface.

LONG TERM (Monday through Saturday):The front end of the long
term remains consistent and in good agreement among the latest
model output. Mid level high pressure anchored over NC Mexico and
Texas remains in tact through Thursday while moving ever so slowly
eastward. Sensible weather will be benign with a very dry
atmosphere in place leading to clear skies overnight and mostly
sunny to partly cloudy conditions during the day with temperatures
running 6 to 12 degrees above normal. Southeast winds starts off
light to moderate with a gradual increase through the week peaking
on Thursday as an upstream mid level trough moves into the
Southern Rockies. Will continue to monitor for wind advisory
conditions developing Thursday with the latest GFS guidance now
indicating winds approaching 30 mph.

Uncertainty creeps into the forecast for days 6 and 7 with the
approach and possible passage of a mid level low pressure trough
and weak cold front. Models have been inconsistent on timing of
these features slowing down there forward motion the last two
days. GFS and ECMWF also begin to diverge on the moisture fields
with GFS on the slightly wetter side with the EC remaining very
dry. With plenty of uncertainty and poor consistency among the
model members will leave the slight chance pops in for Friday and
push them into Saturday as well. Confidence to say the least is
low but there is still plenty of time to adjust as we move into
early next week and the models get a better handle on the
movement of the trough. Temperatures show little change but could
become warmer depending on the track of trough and if the EC and
its drier airmass is the dominate model. In any case, temperatures
will remain above normal through the latter half of the forecast

MARINE:(Now through Sunday Night): A few TCOON sites on the Laguna
Madre are now measuring wind speeds at or above 15 knots, so will go
ahead and hoist SCEC wording for the remainder of the afternoon.
Latest ob from Buoy 020 has SE winds 8-10 knots with seas of about 4
feet.  Generally light-to-moderate SE winds and low-to-moderate seas
expected through Sunday night with high pressure over the north-
central Gulf in control.  No additional marine headlines expected
beyond this afternoon.

Monday through Thursday...Surface high pressure is expected to be
centered over the North Central Gulf Monday and Tuesday producing
a weak onshore gradient across the Western Gulf. The surface
ridge then begins to move east mid week as the supporting mid
level ridge over Texas begins to get shunted eastward as a large
mid level low pressure trough moves into the Southern Rockies. As
a result, the pressure gradient begins to strengthen Wednesday
peaking Thursday and Thursday night. Small craft exercise caution
or small craft advisory conditions are likely at those times as
both wind and seas increase.




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