Area Forecast Discussion
Issued by NWS Brownsville, TX

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000
FXUS64 KBRO 011716 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
1116 AM CST Thu Dec 1 2016

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

&&

.AVIATION...Light winds shifting from northeast to east this
evening and then to southeast by Friday morning will bring a
tongue of higher dew point air over the area in the lowest levels.
MVFR ceilings will develop this evening, with IFR ceilings
possible after midnight, along with light fog, persisting through
daybreak before slowly improving with stronger south southeast
winds.

&&

.PREV DISCUSSION... /issued 553 AM CST Thu Dec 1 2016/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...VFR expected to prevail across the RGV airports
through sunset of this first day of December with winds veering
from NE to E but remaining light to moderate in speed. These
onshore winds will gradually return moisture, with cloud decks
forming at the base of an inversion around 4 to 7 kft by mid-day.
Guidance strongly suggests these CIG`s will lower to MVFR levels
this evening as the low levels of the atmosphere continue to
moisten, with some MVFR mist also possible. MOS and SREF also
indicate a reasonable chance for IFR ceilings to develop late
tonight at MFE as a warm front lifts northward into the RGV.
Isolated showers could also develop after midnight tonight but
expected coverage does not warrant a PROB30 group at this time.

PREV DISCUSSION... /issued 425 AM CST Thu Dec 1 2016/

SHORT TERM (Now through Friday): After a pleasant day on Thursday
(albeit with increasing cloud cover from mid-day onward) with
temperatures just above climatological norms, moisture levels will
be on the increase again tonight and on through Friday.  Lower-end
rain chances return as soon as late tonight for the Rio Grande
Valley.

For today (Thursday), moderate zonal flow continues at jet-stream
level.  Light southerly flow develops at H85, while surface winds
veer to ESE as the surface high currently centered over East-Central
TX migrates eastward to the MO/AL vicinity.  Net effect will just be
increased cloud cover with no rain chances just yet.  Went ahead and
bumped up afternoon high temps a degree or two as inherited values
were a bit below the values realized yesterday.  Even with the
increased cloud cover today, should still be able to exceed those.

Tonight, flow at mid and upper levels begins backing toward the WSW
as a trough digs into the Desert Southwest.  SE flow continues
moisture return at low levels.  Consequently, 00Z runs of both NAM
and GFS prog that precipitable water values will rise to 1.4-1.7"
(highest near the coast).  This is well above the mean for the date
at BRO of 1.1".  Forcing for widespread precip will still be
lacking, though, so kept the previous forecast`s idea of isolated
PoP`s over the RGV and bit higher offshore later tonight.  Also
adjusted tonight`s min temps upward a couple of degrees due to the
increased cloud cover and rapidly recovering dewpoints.  Some hint
in the MOS guidance of mist/fog forming late tonight, but will leave
out of the grids for now as it seems that winds will stay up in the
5-8 mph range with mostly cloudy skies.

Things become a little more interesting as we move into Friday.  As
more energy drops into the base of the Desert SW trough, upper-
levels winds back further to southwesterly.  Surface low pressure
troughing forms in the lee of the Sierra Madre, and the old frontal
boundary currently out over the Gulf moves back through the area as
a warm front...most likely during the morning.  Best isentropic
lifting will occur just north of the area, so reduced PoP`s a bit,
but still will be scattered coverage most areas.  Also will probably
see enough destabilization over the coastal counties for some
isolated thunder to occur...mainly in the afternoon as the area is
left in the warm sector after the warm front lifts northward. Friday
will also be rather humid for the season, as dewpoints range from
the mid-60s NW to the lower 70s SE.  Afternoon temps in the low 80`s
will be common, depending on rain coverage.

LONG TERM (Friday Night through Wednesday): The long term portion
of the forecast is becoming incredibly frustrating. As was the
case 24 hours ago, model guidance is indicating a slower drop of
closed 500 mb low pressure into the Baja Peninsula and northwest
Mexico, the east-northeast progression of that system across Texas
and into the Mississippi Valley, and an associated delayed passage
of a cold front through Deep South Texas and the Rio Grande Valley.
Based on the timing of these major weather features, the best
opportunity for rainfall is anticipated to be Saturday night
through Monday, with numerous showers and thunderstorms forecast
from Sunday night through Monday as the slow progression of the
cold front through the BRO CWFA interacts with deep tropical
moisture that pools in advance of the front. Another frontal
passage on Wednesday will bring another shot of precipitation at
that time. Significant adjustments to daytime high and overnight
low temperatures were made based on the timing of the two cold
fronts.

MARINE (Now through Friday): Buoy 020 reporting ENE winds of 12G16
knots as of 250am CST with seas of 5.5 feet.  Generally moderate
winds continue today and back to SE by Friday as the surface high
over East-Central TX migrates eastward and is eventually replaced by
coastal troughing.  Winds may reach SCEC levels over the outer Gulf
waters on Friday.  Seas persist at mainly 4-5 ft. until Friday
afternoon when they build toward 6 ft...again implying SCEC may be
required.  No Small Craft Advisories are anticipated in the short-
term, however.  Isolated thunderstorms return to the forecast on
Friday afternoon.

Friday Night through Wednesday: The most favorable marine
conditions are expected to occur Monday night through Tuesday
night, with light to moderate winds and low to moderate seas
anticipated, as surface high pressure passes from west to east
directly over the Lower Texas coastal waters. The remainder of
the forecast period will feature adverse winds and seas, with
Small Craft Advisories likely for all or portions of the
adjacent coastal waters of Deep South Texas and the Rio Grande
Valley, due to frontal passages and enhanced surface pressure
gradients over the western Gulf of Mexico. A brief period of
gale-force winds gusts is possible from sunset Wednesday to
sunrise Thursday.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...None.
&&

$$

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