Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 091119

Area Forecast Discussion
National Weather Service Houston/Galveston TX
519 AM CST Mon Dec 9 2019

.AVIATION [12Z TAF Issuance]...

Outside of the Houston/Galveston area, widespread IFR/MVFR
conditions, and with MVFR SCT decks there, even the last remaining
VFR obs should slip to MVFR in the next few hours. Expect only
very slow improvement through the morning, allowing for a few
barely VFR hours across Southeast Texas until an incoming front
causes degradation in flight conditions again.

Deeper into the afternoon, streamer showers will start to become
more common near the coast, with the front sparking even greater
shower chances overnight. There`s an outside shot for a stray
lightning strike, but right now it looks like thunder is not


.PREV DISCUSSION /Issued 352 AM CST Mon Dec 9 2019/...

.SHORT TERM [Through Tuesday Night]...

A thick, broken veil of thick cirrus is making satellite observation
of tonight`s low stratus and fog difficult tonight.
Simultaneously, the cirrus (and some stronger winds) are likely
disrupting the development of fog, and will favor stratus through
the overnight hours. Surface obs show a bit of fog here and there,
but most are seeing low cloud heights - as low as 800 feet in
spots, and closer to 2000 feet in others. This should likely
continue through the night, with the 2000 foot cloud decks likely
to drift downwards to meet the spots with lower cloud bases.

Today, look for southwest winds to continue to pump Gulf moisture
into the area with dewpoints rising up into the upper 60s to
nearly 70 degrees today and tonight. In the meantime, we`ll have
to look out west for our next big weather feature.

Water vapor reveals two upper troughs making their way
through/out of the West. An upper trough dropping off the Rockies
into the Northern Plains is trailing an upper low in the southern
jet stream currently centered near Las Vegas. The northern trough
will support lee cyclogenesis over the Plains, which will then
propagate towards the Great Lakes, with a cold front dropping all
the way into West Texas. While the northern trough and the
location of the surface low will surely be too far away to help
spur unsettled weather, the southern trough will be swooping in
just in time to result in vigorous cyclonic vorticity advecting
over the area, and we may yet catch some benefit from a departing
jet streak.

Timing the front is still a bit tricky, but the general idea of a
Monday night frontal passage is still on track. We`ll see a bit of
instability present this afternoon, but I generally expect it to
be wasted given (west-)southwest flow through the column. We may
see some streamer showers/drizzle crop up over the nearshore
waters and at the coast, but that should be about it.

Rain chances should ramp up significantly overnight as the front
moves into the region. An isolated rumble of thunder isn`t out of
the question, but I left it out of the forecast as the timing is
pretty poor, and the environment doesn`t really support the
maintenance of instability through the night. Though confidence in
a broad area of showers is high, precipitable water is not progged
to be terribly high - generally under 1.5 inches. Given the time
of year, this does bring us into the ballpark of the 90th
percentile, but that and an awkward inflow fetch should limit
rainfall totals. PQPF shows that exceeding a tenth of an inch is
probably a slam dunk, and getting at least a quarter inch is very
likely for all but our westernmost areas. But we see a strong
drop-off in probability of exceeding half an inch, and exceeding
an inch is very unlikely.

.LONG TERM [Wednesday Through Monday]...

Wednesday morning is likely the coldest morning of this week and the
upcoming weekend with temperatures near freezing across parts of our
far northern counties where winds will be the lightest and clouds will
be at a minimum. Elsewhere where there will be a little more wind and
clouds, lows should range from the mid/upper 30s inland to the low/mid
40s at the coast. After high temperatures remain in the 50s for both
Wednesday and Thursday, a warmup is in store for the area with Friday`s
highs in the low/mid 60s and Saturday through Monday`s highs in the
upper 60s/mid 70s. The area`s next best chance of rain in this long
term forecast period looks like it might come around a week from today
(Mondayish) when another cold front moves through the area.  42


Sea fog will gradually become an increasing concern as dewpoints
slowly rise towards water temps in the shallower Gulf and
nearshore waters. Mitigating the concern somewhat is the
expectation for generally southwesterly winds, which is not an
ideal fetch for sea fog. For now, conditions look pretty good on
webcams along shore.

Potential will continue into the day, but will be a precarious
balance of dewpoints, water temps, wind fetch, and rains. For what
it`s worth, more guidance shows fog emerging late this afternoon
and this evening as daytime mixing ends and winds near the coast
back slightly...and perhaps just enough for fog to snap into the
picture. This may not be a great recipe for dense sea fog to form,
but I`d expect at least some fog development today/tonight, with a
short window of dense fog before the front arrives to end the

Though the front will put an end to any sea fog threat, it will
also introduce stronger winds and seas. Onshore flow today will be
very near the SCEC threshold in the offshore waters. And though
the forecast is not quite enough to require that, we`ll look for
strong northerly winds to develop on Tuesday behind the front. The
need for a small craft advisory looks nearly certain at this
range, and came close to issuing a gale watch for the offshore
waters Tuesday afternoon and Tuesday night. Definitely stay tuned
to the forecast for this post-frontal position for the latest on
winds behind the cold front.




College Station (CLL)  81  44  46  34  57 /   0  80  80  10  10
Houston (IAH)          81  52  54  39  57 /  10  90  90  20  10
Galveston (GLS)        75  60  62  45  57 /  10  80  90  30  10






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