Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 211744

Area Forecast Discussion
National Weather Service Brownsville TX
1144 AM CST Tue Nov 21 2017

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


The rest of the afternoon and evening will continue with VFR
conditions with the passing of some high level clouds. Winds
are expected to diminish around sunset with southeasterly to
variable directions. Attention will then turn to a cold front
during the overnight that will result in CIG/VIS dropping to
MVFR conditions, passing rain showers and a north wind shift.
Confidence remains low at the time of this TAF Cycle but IFR
conditions and a few lightning strikes may briefly occur with
heavier rain activity. MVFR conditions continue for Wednesday
morning with low CIG at around 2000 feet. The northerly winds
increase with gusts to near 25 knots during Wednesday morning.



.PREV DISCUSSION... /issued 514 AM CST Tue Nov 21 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Will see some patchy haze/fog and IFR CIGS between
12Z and 14Z this morning mainly over portions of the mid and lower
valley before low level moisture is dissipated by the rising sun.
VFR conditions will then prevail region-wide until at least 06Z
tonight as a dry southwest to west low level flow develops.
Surface winds throughout the day will generally remain at or below
12 knots. Will start to see some MVFR-IFR CIGS develop over the
northern portions of the forecast area after 06Z tonight as a cold
front enters the Rio Grande Valley. This front will sweep
southward through the early Wednesday morning hours.

PREV DISCUSSION... /issued 322 AM CST Tue Nov 21 2017/

SHORT TERM (Today through Wednesday):Northwest flow was in place
aloft over deep south TX early this morning with considerable high
clouds pushing southeast into the region amidst the upper flow.
Temp/dew point spreads were closing mainly at the coastal
observation sites due to residual low level moisture and generally
calm winds. Will have to keep an eye on possible haze/fog formation
early this morning, however the influx of high clouds from the north
will work to delay/inhibit the development of haze/fog before

For the rest of today, a shortwave trough riding down the east side
of a strong upper ridge over the southwest US will dig south and
strengthen over the southern plains. The low level flow over the Rio
Grande Valley will turn southwest, then west in the afternoon, in
advance of a strong cold front associated with approaching shortwave
trough. The change in flow, an influx of drier low level air, and
more sunshine will cause high temperatures to rise noticeably above
values that were reached Monday afternoon. Highs today will
generally be in the lower to mid 80s, which will roughly be 6 to 10
degrees above normal.

For tonight, the aforementioned cold front will enter the northern
portion of the forecast area around 3 am then rapidly push south
through the early morning hours on Wednesday. Clouds will increase
across much of the forecast area in advance of the front and
scattered showers with embedded thunderstorms will develop along and
behind the front. Could see some areas pick up a half-inch of precip
tomorrow morning as the front progresses southward...otherwise not
anticipating any severe weather (large hail or damaging winds) with
any thunderstorms that do develop. Showers and thunderstorms will
diminish through the late morning and afternoon hours as the front
exits the region to the south. Cloud cover, precipitation, and cold
air advection will keep high temperatures Wednesday afternoon
limited to somewhat below normal values ranging from the upper 60s
out west with lower 70s elsewhere.

LONG TERM (Wednesday Night through Monday): The long term could
not be any nicer or quieter as all of Texas will be in between
a high pressure ridge anchored over the Southwest U.S and a low
pressure trough extending over the Gulf of Mexico to the
Midwest/NE. This highly amplified mid level pattern will maintain
a dry northwest to north flow over our region through early next
week. At the surface high pressure will stretch from Deep South
Texas along the gulf coast through Saturday before becoming
reinforced next Sunday and Monday. Models are in good agreement
and consistency with the midlevel and surface features making for
a highly confident forecast. No rain is expected for the long term
with deep layer dry air (layered mean RH below 30 percent)
providing very low humidity days Thursday and Friday. Southeast
winds return for the weekend as surface highs settles to the east
allowing for some limited humidity and clouds to return.

Expect 25-30 degree swings in temperatures Thursday and Friday
as temps start off below normal Thanksgiving morning, day and
into Friday morning before returning to near normal Friday
afternoon. Southeast winds next weekend will take temperatures
back above normal with daytime high exceeding 80 degrees. Models
temperatures guidance is all within a few degrees through the next
7 days giving better then average confidence to the going
forecast. Enjoy.

MARINE:(Today through Wednesday): Modest winds/seas to prevail
today ahead of a strong cold front slated to move across the waters
late tonight/early Wednesday morning. The front will enter the
northern waters around 3 am then rapidly push south through the
early morning hours causing winds to rise solidly into the Small
Craft Advisory range around sunrise Wednesday morning. Waves will
respond to the increase in winds with maximum heights over the outer
waters reaching up to 8 to 10 feet throughout the day on Wednesday.
Instability associated with the front will lead to chances of
showers and thunderstorms over the waters mainly between 4 and 10 am
with chances of precipitation diminishing through the afternoon

Wednesday night through Saturday...Surface high pressure north of
the Gulf coast Wednesday night and Thursday will maintain a modest
north wind and higher sea with possible ongoing small craft
advisories for all or portions of the Lower Texas coast. As the
ridge of high pressure settles along the Texas Gulf coast late
Thursday afternoon and Friday Marine conditions rapidly improve
with fair conditions continuing next weekend.


GM...Small Craft Advisory for winds from 3 AM to 6 PM CST Wednesday
     for GMZ130-132-135.

     Small Craft Advisory from 3 AM Wednesday to midnight CST
     Wednesday night for GMZ150-155-170-175.



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