Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 210517

Area Forecast Discussion
National Weather Service Brownsville TX
1117 PM CST Mon Nov 20 2017

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


.AVIATION...Satellite imagery indicates low-level cloud deck
continues to move eastward over the Gulf waters as a mid-level
shortwave trough exits South Texas. This trend will likely continue
through the overnight with a few lingering low clouds possible. With
lightening winds tonight a few patches of fog will be possible, but
not expecting any local aviation impacts at this point. Tuesday, VFR
conditions will prevail with southwesterly to southerly winds
returning and scattered cumulus during the day.


.PREV DISCUSSION... /issued 606 PM CST Mon Nov 20 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Radar imagery indicates scattered drizzle or light
showers are persisting along the coast and over the Gulf waters
this evening as a mid-level shortwave trough continues to move
eastward away from the region. Kept VCSH for the lower RGV
airports early tonight, but conditions should dry out after
midnight with drier air moving in aloft. A low-level cloud deck
will continue overnight, but VFR flight categories should continue
through the next 24 hours. A few patches of fog are possible
early in the morning, but cloud cover should hinder much of any
development. Winds on Tuesday will shift back to the south in the
afternoon with less cloud cover expected.

PREV DISCUSSION... /issued 211 PM CST Mon Nov 20 2017/

SHORT TERM (Tonight through Tuesday Night): Conditions will settle
down tonight with a few showers possible over the Gulf, but with
clearing skies over land, light winds, and low temperatures in the
50s to lower 60s. Patchy ground fog may be possible here and there
near dawn due to residual ground moisture, light surface winds, and
radiational cooling. Tuesday will be pleasant with high temperature
recover into the lower 80s under mostly sunny to partly cloudy skies
and light southeast to south winds. The next front will be on the
way Tuesday as a Canadian air mass plunges south over the plains
ahead of a large ridge over the western United States. An embedded
mid level short wave trough will roll down the eastern side of the
ridge and into the lower Mississippi Valley/northwest Gulf Tuesday
night, adding some vertical instability to the surface front. North
winds will develop Tuesday night along with scattered convection,
with a few rumbles of thunder possible, as the front pushes through.
Best chance of weather looks like from 3 am to 9 am Tuesday morning
with precip amounts measured in hundredths and tenths of inches, at
most. Cells will be mainly discrete and not overly productive since
not a lot of column moisture will be in place ahead of the event.
Forecast sounding CAPE and shear are not impressive and suggest
ordinary type thunderstorms, should any develop, ahead of or along
the front.

LONG TERM (Wednesday through Monday): The most exciting portion
of the long term forecast will occur during the first 18 hours of
the period, as a 500 mb trough moving through the Mississippi
Valley assists in bringing a cold front through Deep South Texas
and the Rio Grande Valley. Isolated to scattered convection is
anticipated Wednesday and early Wednesday night. Afterwards, mid-
level and surface high pressure building over the region will
produce dry weather for the remainder of the forecast period. Near
normal temperatures initially due to the passage of the cold front
will gradually increase to well above normal levels for the second
half of the long term period.

MARINE (Tonight through Tuesday night): Relatively quiet marine
conditions will be on tap through Tuesday with mid level ridging
upstream and broad high pressure over the northwest Gulf.
Southeast to south winds will shift to north Tuesday night with
increasing convection over the marine areas due to an approaching
cold front supported by a digging, positive tilt, mid level short
wave trough over the northwest Gulf. North winds will strengthen
to small craft should exercise caution territory of 15 to 20 knots
near dawn Wednesday morning, possibly a bit more over the
northern waters, but advisory criteria conditions will more likely
develop Wednesday during the day once the front is firmly through
the area (see next section).

Wednesday through Monday: Adverse marine conditions, featuring
Small Craft Exercise Caution and Small Craft Advisory, are indeed
expected Wednesday and Wednesday night due to the passage of a
cold front. Improved and much more favorable winds and seas are
then likely for the remainder of the forecast period due to
building and persistent mid-level and surface high pressure.




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