Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 192329
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
629 PM CDT Sat May 19 2018

.AVIATION...
Scattered VFR ceilings remian over the area as moderate
southwesterly to southerly flow continues. Expect cigs to lower to
MVFR from south to north tonight. As winds go calm late tonight
over the northern airports, some patchy fog could develop, but
confidence in timing and extent is low at this time. VFR cigs
return tomorrow with calmer winds than today, no gusts expected.
Scattered showers and an isolated thunderstorm may progress into
the northern areas tomorrow afternoon. Kept vcsh mention only at
CLL, as coverage should be sparse elsewhere. 22

&&

.PREV DISCUSSION... /ISSUED 344 PM CDT Sat May 19 2018/

DISCUSSION...

Summer-like conditions have returned to Southeast Texas, and if
you don`t know, well now you know. Also, if you didn`t know, how
have you not stepped foot outside this week? The main change for
the coming week will be the return of small chances of rain
showers or a thunderstorm during the days, which really was not a
realistic hope for most this past week. However, don`t get too
excited - given the setup, isolated to scattered development may
be the best to hope for, with the best shot arguably coming
tomorrow (especially up northwest towards College Station). Deeper
into next week, the models diverge pretty significantly, giving us
a plausible scenario for two very different stories: either a
weak, backdoor cold front to hold temperatures steady; or the
return of a big ridge to crank the temperatures back up. For now,
the forecast leans towards the latter.

NEAR TERM [Through Tonight]...

Another warm day in the area, though temperatures well inland are
more in the upper 80s/lower 90s rather than the lower to middle
90s. Nearer the coast, temperatures are more in the 80s, which
looks to be keeping the land/water temperature differential
smaller and the seabreeze in check very close to the coast.

Tonight, first look for the scattered to broken afternoon cumulus
to give way to clearer skies, but by the end of the night, a deck
of low clouds looks to develop. Between that and dewpoints in the
lower 70s, look for lows tonight to be held above seasonal norms
and in the 70s, perhaps even around 80 degrees on the immediate
coast. Patchy fog may also develop in rural spots ringing the
Houston metro, which should stay a bit warmer, thus clearer than
the surrounding rural areas.

SHORT TERM [Sunday Through Monday Night]...

While we`re having a relatively toasty night, a complex of
thunderstorms along a cold front over Northwest Texas will be
traveling to the Southeast. There is a chance some of those may
survive to the northwest portions of our area, but the front will
stall well short of us, and the convection should be fizzling as
it makes its way near us. Still, it probably gives areas up around
College Station, Brenham, maybe Livingston a bit better of a
chance for rain than closer to the coast. It does appear there
will be a weak shortwave trough moving through that may help get
some showers going, but it doesn`t look super impressive upstream
on water vapor imagery right now, and that underwhelming
appearance generally holds in the model guidance. But, all things
considered, I do at least hold temperatures similar to or ever so
slightly lower than today`s highs.

Not really looking for much change Monday - lows above normal,
highs hanging out around 90 away from the water, and a chance of
some isolated to scattered showers and storms. Given that we`re
again looking for a boost from a subtle shortwave, I`m continuing
the trend of undercutting guidance some on the PoPs again,
especially as we`re now starting to get some range on this
forecast. I`d love to be able to tell you I can nail the timing of
a subtle upper trough 48+ hours out so that it perfectly
coincides with the strongest instability of the day to maximize
upward motion...but I can`t realistically do that. In more general
terms, I`d say that the chances of shower and thunderstorm
development will be near or slightly better than your typical
summer day.

LONG TERM [Tuesday Through Saturday]...

This pattern of weak upper troughs potentially pairing up with the
diurnal pattern to produce isolated to scattered showers will
continue into the midweek, but you can see the models implying
that ridging will be starting to take over with modestly
increasing midlevel heights over the area. This manifests in
slightly lower PoPs - especially southwest of Houston towards
Matagorda - and a very slight warming trend back into the lower
90s across the area.

In the back half of the week, the guidance begins to diverge
dramatically. There`s growing unanimity that some sort of low
pressure area (whether tropical or not TBD) will lift into the
Gulf out of the Caribbean Sea. The GFS retrogrades an upper low
back our way, which shunts the surface low way off east of
Florida, and may even help ventilate it for some tropical
development. While the surface low will have zero impact on us,
the falling heights from the retrograding upper disturbance will
allow for better rain potential, and even brings a weak, backdoor
front to the area this weekend. It shouldn`t do much to cool us
down, but may hold temperatures in check.

The Euro, on the other hand, has dramatically different ideas. It
digs the trough over the Eastern US, and strong ridging builds
over Mexico and the Desert Southwest, and gives us rising - not
falling - midlevel heights. This would keep us drier and turn the
dial on the temperature back up. FWIW, the Canadian gives us a
setup more like the Euro with a surface track a little more to the
right, but also is more aggressive in development like the
GFS...which is weird. Given recent trends and the time of year,
I`m leaning towards siding with the Euro, and the forecast puts us
solidly back up into the lower and middle 90s by the end of the
week. But...do keep some 20 to 30 percent chances of rain through
the week just in case the GFS might be on to something here.

MARINE...

Southeasterly flow continues as pressure remain low over West Texas
with LLJ axis extending from near Brownsville to Dallas this
afternoon. Winds of 10 to 15 knots will be common through sunrise
and for at least a few hours will peak in the 15-20 knot range
mainly Matagorda Bay area southward and well offshore tonight. Seas
of 3 to 5 feet should be the norm tonight. Winds gradually
diminishing Sunday through Monday and backing slightly as weak high
pressure settles into East TX. Light wind regime should take hold
Monday through Wednesday. Will be keeping an eye on the Caribbean
and Eastern Gulf with large tropical surge of moisture stalling near
the Yucatan/Eastern Gulf/Northeastern Gulf region and just hanging
out for a few days.

45

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      74  91  71  91  70 /  10  30  10  30  10
Houston (IAH)              76  91  73  92  72 /  10  30  10  30  10
Galveston (GLS)            80  86  78  85  78 /  10  20  10  20  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 9 PM CDT this evening
     for the following zones: Coastal waters from Freeport to
     Matagorda Ship Channel TX out 20 NM...Matagorda Bay.

     SMALL CRAFT SHOULD EXERCISE CAUTION through Sunday morning for
     the following zones: Waters from Freeport to Matagorda Ship
     Channel TX from 20 to 60 NM...Waters from High Island to
     Freeport TX from 20 to 60 NM.

&&

$$

Discussion...31
Aviation/Marine...22



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