Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 261134
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
634 AM CDT Tue Sep 26 2017

.AVIATION...
TAF sites are VFR early this morning with some high clouds streaming
across the area from the west. Could see a little bit of fog development
in the next hour or two. If high clouds don`t interfere, some SHRA
development will be possible with daytime heating with the greatest
coverage this morning expected mainly out west and this afternoon along
any sea breeze boundary that moves inland. Quiet tonight with patchy
fog possible again inland areas.  42
&&

.PREV DISCUSSION... /ISSUED 340 AM CDT Tue Sep 26 2017/

DISCUSSION...

Largely seasonable weather for much of the week is expected, though
some indirect impacts to our area may be seen thanks to a
potentially prolonged precipitation event far to our west over
portions of South Texas and northern Mexico. More significant change
looks to come at the end of the week as a front backdoors through
the area, followed by an influx of drier and slightly cooler air.
However, fans of fall weather shouldn`t get too excited, as the
impact of high temperatures will be pretty modest, and more summer-
like conditions look to return early next week.

NEAR TERM [Through Today]...

The radar is fairly quiet across the area late tonight, though a
couple showers are present over Jackson County where slight chance
PoPs are in place. However, the bulk of the rain in the region is
far to our west where an MCS has developed. In GOES-16 IR imagery,
the coldest cloud tops on the Mexican side of the US-Mexico border
are as cold as -82 C as of 3am. Closer to home, observations show
some patchy fog around, mainly west of the Houston metro. Expect
more of that patchy fog to crop up until shortly after dawn. A few
spots here and there could get fairly dense, as we`ve seen the past
few days, but don`t expect any widespread dense fog.

Precipitable water looks to be near 2 inches around Matagorda Bay
today, decreasing up the coast to be as low as 1.5 inches around the
Bolivar Peninsula. With an achievable convective temp, we certainly
should expect to have some sort of shower/storm development today,
with the best chances towards the southwest and where any seabreeze
will provide additional lift. We`ll have to watch the behavior of
the MCS to our west carefully. Short range models suggest that the
system will persist through the day, potentially initiating a
mesoscale convective vortex (MCV), but stay well to our west.
Indeed, these models are rather dry in our area - perhaps with so
much of an upward mass flux out there, we`ll see compensating
subsidence over us, overcoming the more subtle convective triggers
we`ll be looking for. I did nudge PoPs down somewhat because of
this, but because of the environment and models` issues in handling
MCVs, I`m not ready to buy into the area being totally dry today.

Regardless, the amount of cloud and rain development doesn`t seem
likely to seriously deter rising temperatures this afternoon, so go
with highs in the upper 80s to around 90. Wouldn`t be surprised to
see us go even higher if we do see compensating subsidence tomorrow,
surely keeping us drier and sunnier.

SHORT TERM [Tonight Through Thursday]...

Any convection should come to an end quickly near sundown, leading
to another generally dry night. Skies might not clear as much if we
see much in the way of blowoff debris clouds from the convective
activity to our west. Between that and humidity keeping a high
floor, expect some warm overnight lows.

More or less expect repeats Wednesday into Thursday as a weak
midlevel high looks to set up over the Texas Gulf Coast, while MCSs
either persist or renew in the border region far to our west. But,
change is on the way thanks to a surface low moving across the Great
Lakes region into eastern Canada, trailing a long, weak cold front
that should backdoor into Texas sometime on Thursday. The current
forecast shows a wind shift Thursday morning, though this front
looks fairly diffuse/weak, and so precise timing might be fairly
tough to nail down for a bit yet. Of course, since this is a fairly
diffuse and weak boundary, the precise timing is also probably not
very important.

LONG TERM [Thursday Night Through Tuesday]...

It takes a little more time for drier air to filter in behind this
weak front - a very subtle vort max looks to scoot through Friday
night/Saturday morning, which may help encourage more robust
northeast flow, and hastening the decline of dewpoints into the
50s...at least inland. Between the northeast flow and a continued
weak midlevel high over the Texas coastal region, think the end of
the week into the weekend should be pretty dry. Low temperatures
should be modestly cooler, but think the lack of a real shot of cold
air and increased sun will prevent much of a hit in high temps this
weekend.

Onshore flow should resume in the vicinity of late Sunday, which
likely means the early part of next week will be much more
reminiscent of these past several days and a seasonable late
summer/early fall pattern. The guidance seems fairly gung ho on
scattered to numerous showers and storms Monday and/or Tuesday. But
with the guidance also pretty unanimous on ridging aloft, I`m not
ready to go that high at that range. GFS precipitable water is
progged to be near/over two inches though, so will compromise with
slight chance PoPs that run roughly equivalent to climo. Highs in
this forecast remain in the mid to upper 80s, but I could see having
to nudge that up or down if a distinctly rainier or sunnier picture
emerges, respectively.

MARINE...

Light to moderate east to southeast winds along with seas in a 1 to
3 foot range will continue through Wednesday night. Winds will
become more northeasterly beginning on Thursday with the approach
and eventual passage of a cold front. This moderate northeast flow
(some caution flags might be needed) along with building seas can be
expected at the end of the week and on into the upcoming weekend.
With an anticipated prolonged northeasterly fetch on already
slightly above normal tides, some minor coastal run up issues might
develop as early as the end of the week and possibly extending into
the start of next week.  42

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      90  74  90  73  89 /  20  10  20  20  20
Houston (IAH)              90  75  90  73  90 /  20  10  20  20  20
Galveston (GLS)            88  80  88  79  87 /  20  10  20  20  20

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...NONE.
&&

$$

25/42



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