Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 240247
AFDHGX

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

.DISCUSSION...
A few minor updates were made to account for the latest trends.
Otherwise, the previous forecast appears to be on track. Expect
low ceilings to fill back in later this evening with some isolated
to scattered showers possible in the early morning hours.
Temperatures should remain fairly steady through the night. Some
patchy fog will be possible inland in the morning but should not
be nearly as dense as we`ve seen the past few days. However,
periods of dense sea fog are possible near the coast overnight. 11

&&

.PREV DISCUSSION... /ISSUED 541 PM CST Fri Feb 23 2018/

AVIATION [00Z TAF Issuance]...

Visible satellite shows mainly stratocumulus cloud streets with
some gusty flow at times. Overall stuck in the same pattern as the
last couple of days so look for IFR/MVFR ceilings primarily after
04-06Z tonight. There is an approaching jet streak and shortwave
coming into Texas after 06Z so there may be some showers across
the area during the morning with most of the activity over north
Texas. MVFR/IFR decks may hold on until 16-18Z when winds begin to
mix and likely have some 25 knots gusts tomorrow afternoon.
Frontal boundary begins to work into the area around 21Z tomorrow
based on hi-res WRF models. Capping should be strong to limit deep
convection but may not be quite as strong for an area near KCLL
and KUTS so included VCTS for those TAFs. Otherwise look for the
front to affect the other terminals 00-06Z Sunday. Likely keep
VCSH for those terminals with limited instability and capping
still in place.

The KGLS TAF is a whole another planet which will contend with
sea fog most of the day so expect prolonged LIFR/IFR conditions
until the front can push off the coast likely early Sunday
morning. Even then, the fog may not complete go away.

Overpeck

PREV DISCUSSION /Issued 326 PM CST Fri Feb 23 2018/...

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
morning.

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.

MARINE...

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.

Huffman

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      71  66  74  50  65 /  40  20  70  20  50
Houston (IAH)              79  70  78  59  66 /  20  20  40  60  80
Galveston (GLS)            75  67  72  61  66 /  20  10  10  70  70

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
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...Galveston Bay.

     SMALL CRAFT SHOULD EXERCISE CAUTION until 6 AM CST Saturday 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.

&&

$$

Discussion...11



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