Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 160105 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
805 PM CDT Thu Mar 15 2018

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


.AVIATION...The 00Z BRO sounding shows a pretty dry atms aloft
with a narrow layer of decent moisture return down around the 850
to 950 mb levels. The latest NAM forecast soundings show that the
low level moist deck will thicken up overnight through Fri morning
which will allow the ceilings to lower down to IFR levels.
Increasing daytime heating tomorrow will help mix out the moist
low levels allowing the ceilings to return back to VFR levels late
in the forecast period.


.PREV DISCUSSION... /issued 242 PM CDT Thu Mar 15 2018/

SHORT TERM (Tonight through Friday Night): The base of a
mid level ridge axis over Texas will fade to the east as surface
high pressure over the Gulf flattens. A mid level short wave
trough and associated surface low will eject east from the lee of
the Rockies on Friday. Drier air from the extreme southwest US
will edge into west Texas tonight and then across most of northern
Texas on Friday, pushing also into the ranchlands and brush
country of the CWA Friday afternoon. Isolated coastal showers may
hang on into this evening with the stronger return flow, but rain
chances should be very meager for Friday and Friday night. May see
patchy fog across the ranchlands and brush country tonight, with
slightly more expansive coverage Friday night. Looks like the mid
level pattern will continue to support capping and locking in low
level moisture. The dryline could push into the upper valley on
Friday, but enough moisture will push back Friday night to support
patchy fog. A warming trend will continue, with low temperatures
well into the 60s and high temperatures Friday pushing into the
lower 90s out west. The inherited forecast was in pretty good
shape and only freshened it up with the latest model consensus.
The addition of overnight fog in spots for both nights was the
main update.

LONG TERM (Saturday through Thursday): Going into the weekend
will be very warm across Deep South Texas and the lower Rio
Grande Valley with temperatures ranging from the lower to middle
90s out west to lower to middle 80s right along the coastline as
surface return flow continues between high pressure over South
Florida and low pressure along the leeside of the Rockies. Aloft,
progressive westerly or slightly south of due westerly flow is
expected. This should leave much of the mid levels dry, however,
there may be just enough boundary layer moisture in the southeast
flow for some "streamer" showers to develop. Confidence is low
and any precipitation will result in very little QPF, in fact kept
POPs silent through the weekend.

A cold frontal boundary will begin to move southward
and through the region early next week. There are some pretty
important differences between the GFS and ECMWF with the GFS
being a little less diffuse (it will be rather passive regardless
given the zonal flow aloft) and faster than the ECMWF. Timing
will need to be watched, however, impacts look about the same. As
the front moves through little precipitation if any is expected
and temperatures behind the front should drop out of the 90s and
back into the lower and middle 80s (average for this time of

The remainder of the week looks to be dry with temperatures
remaining around average as northwest upper level flow develops
overhead and surface high pressure dominates the western Gulf.

MARINE (Tonight through Friday Night): Southeast winds have
strengthened a bit over the Gulf this afternoon, and small craft
should exercise caution conditions are in place and will continue
into this evening. The wave models are building seas to seven feet
offshore tonight, so a decision will need to be made on whether
to hoist an advisory for what would be low end conditions. Winds
from the south should weaken Friday and Friday night as Gulf high
pressure retreats east and the plains storm system tracks toward
the midwest and Great Lakes.

(Saturday through Thursday): Light to moderate winds/seas early
in the period will evolve into rather benign marine conditions by
late Saturday and into Sunday. This will not last long as a cold
frontal boundary moves southward toward the region. At this point,
there is some uncertainty just how strong the front will be and
exactly when it will pass through the region, however, moderate
northeast winds and seas will likely occur upon its passage. The
frontal passage should remain rather dry, however, can`t rule out
an isolated shower or clap of thunder or two.

Moving closer to the end of the period, surface winds will begin
to lighten as high pressure builds southward into the western
Gulf. This will produce relatively calmer winds and seas for our
nearshore waters.




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