Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 232126

Area Forecast Discussion
National Weather Service Houston/Galveston TX
326 PM CST Fri Feb 23 2018


The spring-like roller coaster continues, with a cold front
dropping in this weekend and stalling near the coast. This may
make Saturday a good day for those north of Houston to find some
indoor activities, while coastal areas may be lining up more
indoor time on Sunday. This will also briefly cool us down, but a
warm front Tuesday will push us back up for the midweek until we
see the next cold front near the end of the work week. While rain
opportunities will continue to be plentiful this week, potential
for severe weather or heavy rain looks to be fairly limited. Like
the last couple fronts, the best potential for higher impact
storms will be to our north and east. Still, those in the eastern
portion of the area (I-45 or so eastward) will want to stay atop
the forecast for any changes, as we can`t rule out being clipped
by the fringe of the heavier storms.

.NEAR TERM [Through Tonight]...

After a stretch with plenty of showers and some storms to be
found, today has been relatively dry (albeit foggy this morning).
In fact, as the warm front has moved into all but the northernmost
fringe of our forecast area, we`ve even seen low stratus give way
to numerous streets of cumulus clouds. While still pretty cloudy,
this has allowed for streaks of mythical blue sky to be seen here
and there.

This shouldn`t be likely to last long. Once we lose diurnal
heating and the boundary layer starts to collapse, continued
onshore flow and gentle upglide means we should look for low
clouds and some fog to return across the area. Sea fog (more on
that below) should come back in to impact coastal areas this
evening, with more fog developing across the area overnight. Winds
do look a little bit stronger, which may encourage enough mixing
to keep fog not quite as dense as it was last night and this

.SHORT TERM [Saturday Through Sunday Night]...

Saturday might turn out to be an interesting day, but probably for
areas north of here. Low pressure looks to form up around
Northwest Oklahoma, and move up into Kansas through the day,
trailing a cold front down into Texas. Meanwhile, we`ll get some
help aloft with a shortwave trough riding up in the subtropical
jet to be quickly followed by an upper trough in the northern
stream dropping off the Rockies, and rolling through the Central
Plains on its way towards the Great Lakes. And if that`s not
enough, we`re looking for a potent jet streak in the subtropical
jet to move in, as well. But, an astute eye will note I`m mostly
talking about areas north of us, and it probably won`t help that
we`re more likely to be under the right exit region of the upper
jet rather than the left exit region, which tends to be more
correlated with convergence/sinking motion aloft, rather than
upward motion.

This setup means much more to areas from the ArkLaTex up into the
Midsouth much more than us. Still, those way up north around
College Station or Crockett may want to keep an eye on the
forecast tomorrow. If the front`s a little faster, the upper
trough digs a little more, that jet comes in a little more
flat...maybe some of that threat nudges down our way some. More
likely, those areas will see rain, but rather the decaying
structure of whatever happened on the front earlier in the day.

The front will continue to push through the area tomorrow night,
reaching the coast by Sunday morning. And from there, it doesn`t
really go anywhere for the rest of the day. This sets up a narrow
axis near the coast where we still have plentiful warm sector
moisture and warmth, while the upper jet streak has moved on
enough to put us in something more approximating the right
entrance region, which is a bit more supportive of upward motion.
By this point, though, the front over us will be cut off from the
most potent part of the trough aloft, which will limit potential
for strong storms or heavy rain. We are more likely to see a
prolonged period of training showers and storms that are light to
moderate in intensity. As long as rain rates don`t get too
excessive, we should be able to handle this pretty well. With the
mix of mitigating and aggravating circumstances here, the marginal
risk for excessive rain WPC has in their day 3 outlook looks
appropriate, and perhaps is even a bit aggressive.

.LONG TERM [Monday Through Friday]...

Another upper trough swings through the Plains early next week,
and ushers in much drier air, and end to rain chances, and maybe
even -gasp- some sunny skies...for Monday, anyway. Because things
remain pretty progressive, we`re looking for a warm front to
restore onshore flow and bring another pretty solid shot at some
showers and a few storms as early as Tuesday, along with a return
to temperatures in the 70s for the mid-week. But not to be left
out, we see another upper trough come out of the mountains,
accompanied by our next cold front for late next week. The Euro
continues to dig this upper trough much deeper towards the Red
River. The GFS is also a bit deeper, but generally resembles more
the established pattern of swinging quickly up to the Great Lakes.
Either way, there looks to be enough oomph with this front for it
to clear through the region more effectively, and have a 1020s
high settle into Texas behind it for the end of the week. One
might think that this gives a better opportunity for a cool, dry
stretch...and it may...but it`s worth noting that even here we
still fail to see a real prolonged period of cold air advection,
so it may help to temper expectations on any post-frontal
cooldown. There`ll be cooler weather for sure, but there`s mixed
evidence at best for any real cold shot.


.AVIATION [18Z TAF Issuance]...

Visible satellite imagery late this morning shows ceilings
beginning to scatter at CXO, IAH, HOU, SGR, and LBX. Intermittent
MVFR conditions will be possible at these terminals through early
afternoon but decent mixing will allow for VFR conditions to
prevail for at least a few hours before sunset. Daytime heating
may also contribute to isolated SHRA developing near these
terminals this afternoon.

VLIFR conditions continue to impact CLL and UTS (located north of
a stationary boundary also evident on visible satellite bisecting
Southeast Texas from VCT to LFK) and are expected to linger
through mid- afternoon before the stationary boundary begins to
lift north as a warm front and allows for ceilings to lift to
MVFR. Periods of VLIFR sea fog will continue to impact GLS through
the afternoon. Webcams have shown some improvement around the
island and expect a window for IFR/MVFR this afternoon before fog
rolls back in this evening.

A developing 40 knot low level jet overnight and associated
mixing should help mitigate against overall fog potential, but
should result in ceilings lowering to IFR after 06Z. Associated
moisture advection may result in a few SHRA developing again early
Saturday morning.

Southerly winds 8-12 knots this afternoon should decrease into
the 6-10 knot range after sunset. Southerly winds are expected to
increase into the 10-15 knot range during the day Saturday ahead
of a cold front approaching the terminals after 21Z.




Webcams and platforms show fog has thinned or cleared around
Matagorda Bay and the nearshore waters west of Freeport, with dense
fog still being observed in the lower Galveston Bay and nearshore
waters east of Freeport. Short-term guidance has consistently
underestimated dew points across the waters today and with dew
points remaining in the upper 60s with backed winds, expect fog to
redevelop and thicken closer to sunset. Have reconfigured the marine
Dense Fog Advisory by adding Galveston Bay back to the ongoing fog
advisory and extending the advisory through 6 AM CST. With southerly
winds just off the surface (1000-2000 feet MSL) increasing to 30-35
knots early Saturday morning, concerned that mixing may cause fog to
lift or clear earlier than anticipated. Elevated onshore winds will
also result in caution flags for the offshore waters tonight. This
southerly flow will help keep fog limited on Saturday with periods
of fog returning Saturday night ahead of a cold front.

The cold front looks to make a run for the coast Sunday morning,
remaining near or just off the coast on Sunday. Where the cold front
ultimately ends up will have big implications for sea fog potential
late this weekend. If the front clears the coast, a break in the sea
fog will be possible Sunday night into Tuesday. If the front lingers
along the coast, sea fog may persist into the middle of the upcoming
week. With the front near the coast on Sunday, showers and
thunderstorms will be possible.




GM...Dense Fog Advisory until 6 AM CST Saturday for the following
     zones: Coastal waters from Freeport to the Matagorda Ship
     Channel out 20 NM...Coastal waters from High Island to
     Freeport out 20 NM.

     through late tonight for the following zones: Waters from
     Freeport to the Matagorda Ship Channel from 20 to 60
     NM...Waters from High Island to Freeport from 20 to 60 NM.

     Dense Fog Advisory until 6 AM CST Saturday for the following
     zones: Galveston Bay.



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