Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 182139

Area Forecast Discussion
National Weather Service Houston/Galveston TX
339 PM CST Tue Dec 18 2018


Dense fog from overnight has mostly transitioned to cloudy skies, as
well as some very light showers over the lower Gulf and immediate
coast in the vicinity of Matagorda Bay. Rain and a smattering of
storms will increase in coverage through the night, before winding
down to a return of fair weather for the back half of the week.
We`ll be watching the period around Christmas closely for another
shot at some showers.

.NEAR TERM [Through Tonight]...

A dreary day today as widespread dense fog has given way to
overcast skies for much of the area - though the cirrus deck in
the northwest has even broken enough for some sun to peak
through (don`t get too attached to that, BTW). The radar is
beginning to show echoes around the lower Gulf coast and in the
Gulf waters off Matagorda. Over land, this pattern looks a bit
more drizzly, and haven`t noticed much -RA reports in the obs
except briefly at Palacios.

Water vapor imagery indicates these returns are probably
associated with a very subtle shortwave trough moving across the
area, and should scoot out late this afternoon to this evening.
The next shortwave to keep an eye on is currently over Mexico,
rounding the base of the upper low. As it moves in, it should spur
another round of showers associated with a developing coastal low,
with a handful of thunderstorms....though getting the instability
for storms may be a bit tough. Regardless, as the upper jet
nudges into a more favorable position than it is now, the next
shortwave should be more effective in generating precipitation
than this current one. Precipitation should be generally light,
but we could pile up to around a half to two- thirds of an inch
way up in the north from College Station, through Madisonville to
Crockett. As skies cloud up again, look for temperatures tonight
to stay considerably warmer than previous nights.

.SHORT TERM [Wednesday Through Thursday Night]...

Though I`m unsure just how quantitatively on the HRRR is at this
point, it`s general idea of having more showers in the north, and
fewer to the southeast looks reasonable, along with a bit of
drying in the southwest. Neither the upper trough nor the surface
low look to be in a hurry to get out of here, which will keep
lingering showers in the picture through much of the day -
particularly along and east of I-45.

Eventually, as a stronger jet streak rolls in from upstream to
kick the upper trough out, look for things to dry out late
Wednesday night and through the large majority of the weekend
thanks to deep, onshore flow. The incoming wind fields suggest a
wind advisory may be needed, with sustained winds on Thursday
topping out in the vicinity of 25 mph. If we`re looking at a
situation where the blend of guidance used is blunting the
extremes a little bit, the wind advisory will be needed. If things
instead come in a bit calmer, we may be able to skate by.

Clouds and possible rain will make for a cooler Wednesday, but
Thursday may be even colder if skies can clear early enough on
Wednesday night to allow for some more effective radiational
cooling overnight. Though cold advection looks to shut off
Thursday afternoon or Thursday evening, clearer skies and calmer
winds will almost certainly result in Thursday night/Friday
morning bringing our coldest lows.

.LONG TERM [Friday Through Tuesday]...

As a shortwave ridge weakly builds in over Eastern Texas on
Friday, we should begin a slow warmup Friday, picking up Saturday
as the ridge axis pushes east and we get some southwesterly 850
flow. Highs in the southwest may reach back to around 70 for the

The next weathermaker to watch will come early to mid next week.
The guidance is starting to give us a bit more coherent of a
picture on this scenario, though there are still some fairly
significant uncertainties remaining this far out. But, with some
prolonged onshore flow from the weekend into the early week, we
may build moisture enough to generate some low showers underneath
capping aloft while another upper trough in the northern stream
moves by. All in all, both the GFS and Euro are painting a picture
that is reminiscent of our current setup. But, with the upper low
in the northern stream rather than the southern stream, things
would be less amped up, a weaker coastal trough, and ultimately
less QPF.


.AVIATION [18Z TAF Issuance]...

Dense fog prevailed across much of SE Texas this morning and is now
fading off. Early this morning, most sites were at 1/4SM VV002 and
prevailed through around 17Z. vis/cigs are finally transitioning
to VFR. Today, a warm air advection pattern with winds shifting
more southerly, which will help enhance moisture transport, can be
expected. By tonight, SHRA activity is expected to affect most -if
not all- TAF sites through Wednesday as an upper level trough
approaches from the NE. A few isolated TSRA cannot be ruled out,
thus, VCTS could be added during the 06-15Z period in the upcoming
TAF issuances, but confidence remains low. At the moment, PROB30
are in place for most TAF sites for possible IFR vis/cigs due to a
mix of -RA/BR tonight.



A coastal surface low pressure is expected to move across the waters
Wednesday, increasing shower activity with the possibility of a few
isolated thunderstorm. Thursday morning, an upper level trough with
an associated cold front will move into the waters tightening the
local pressure gradient. This may result in strong NW winds of 25-33
KTS Thursday afternoon through Thursday night and elevated seas of 6-
10 feet. SCEC/SCA will likely be issued for the bays and Gulf waters
Thursday through Friday. A Gale Watch would be issued later today or
tonight if the current forecasted wind speeds increase or remain
near Gale Warning criteria. Moreover, due to the strong
northwesterly wind flow, a Low Water Advisory could be issued for
the bays late Thursday through Friday as water levels could reach 2
feet below MLLW. Marine conditions are expected to improve by Friday
afternoon. 24



The Trinity River continues to have the only points in flood stage,
with Liberty now on the cusp of falling from major to moderate
stage, and Moss Bluff falling through minor stage. Both sites
crested last week and are still slowly falling. Barring any future
rises, both points are forecast to fall below flood stage by the end
of the week. As it stands, the forecast rainfall tonight should not
be enough to cause any rises, but as always, river levels are very
sensitive to small changes in the amounts and locations of rainfall,
so be sure to keep up with the latest forecast to ensure a continued
downward trend.



College Station (CLL)  53  63  48  61  40 /  80  60  10   0   0
Houston (IAH)          54  65  50  61  42 /  70  70  20   0   0
Galveston (GLS)        59  66  54  62  47 /  60  60  20   0   0






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