Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 151726
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1226 PM CDT Sun Oct 15 2017

.DISCUSSION...

18Z AVIATION...Northerly winds will increase this aft and eve
behind the front to around 15 KTS with higher gusts as it
progresses southeast. The front is nearing UTS and has passed CLL.
Should reach GLS late this aft. A couple of hours of MVFR
ceilings are expected behind the front across inland areas this
afternoon. Isolated shra possible along the front and just
behind it as well, but coverage looks very minimal. Will see NE
winds 15 to 20 KTS tomorrow morning once heating begins. 33

&&

.PREV DISCUSSION... /ISSUED 1024 AM CDT Sun Oct 15 2017/

DISCUSSION...
The cold front is steadily approaching from the northwest and shows
up nicely on visible satellite as it begins to pass through the
northern parts of our CWA. There are a few sparse showers along the
leading edge of the front, so chances for precip were lowered to
isolated through this afternoon. Liked how the HRRR and RAP handled
the morning precipitation the best, so these were used for this
afternoon/evening.

An additional area of precipitation is possible this afternoon along
the coast as the onshore flow persists ahead of the frontal passage.
This afternoon and evening, showers and thunderstorms are most
likely offshore near the area of precipitable water over 1.7". Rain
chances quickly diminish across the area tonight into tomorrow.

The inherited temperature forecast was not altered, with high temps
today ranging from upper 70s farther north to mid to upper 80s closer
to the coast.

22

PREV DISCUSSION... /ISSUED 641 AM CDT Sun Oct 15 2017/

AVIATION...
Reduced vis due to FG still anticipated across all TAF sites this
morning besides GLS. Light winds are already out of the north,
ahead of the approaching frontal boundary. The cold front nearing
SE TX has picked up speed, and should near the CLL by mid morning.
A line showers ahead of the front could potentially hold together
long enough to impact CLL, so decided to include VCSH from
14-16Z. Short term guidance such as the HRRR and RAP13 indicate
this line dissipating as the front continues to track to the SE.
Therefore, kept VCSH out of the remaining TAF sites for now,
besides at GLS to account for the few isolated showers approaching
from the coastal waters this morning, prior to the passage of the
front.

Moderate to strong northeasterly winds will pick up behind the
front,  which is expected to reach IAH by midday. Closer to the
coast near GLS, conditions could get quite gusty as we head into
the late evening hours. VFR conditions will follow in the wake of
the front as high pressure builds back in from the NW.

Hathaway.

PREV DISCUSSION... /ISSUED 529 AM CDT Sun Oct 15 2017/

UPDATE...
Quick update to issue a Dense Fog Advisory for areas north and
west/southwest of the Houston metro where patchy dense fog has
developed. Webcams show visibilities fluctuating between clear and
near zero within the advisory area and motorists are urged to use
caution when encountering fog banks. Visibilities are expected to
improve after sunrise.

Huffman

PREV DISCUSSION... /ISSUED 341 AM CDT Sun Oct 15 2017/

DISCUSSION...
A cold front is surging southward across northern and western
Texas early this morning, draped along a Midland-Abilene-
Gainesville line as of 3 AM CDT. Simple extrapolation of current
frontal motion brings the front into the forecast area after
sunrise and Houston metro by mid morning, but with surface
pressure rises behind the front beginning to decrease (now around
6 mb/3 hours) expect this frontal timing to slow a bit. With this
in mind, expect the front to reach the Brazos Valley sometime
between 8-11 AM and the Houston metro between 12-3 PM before
reaching the coast late afternoon.

Ahead of the cold front, clear skies and light winds have allowed
for another round of radiation fog to develop. Slightly drier air
that advected into the region from the Gulf yesterday has
minimized the development of widespread dense fog this morning,
but a dense fog advisory may be needed for a period of time this
morning should more development occur. Temperatures will also warm
quickly ahead of the front today, potentially rising into the mid
to upper 80s across the southern two-thirds of the region. Highs
today will be largely dependent on the speed of the front as well
as cloud cover and temperature trends may need to be updated later
this morning based on the front`s progress.

With the best upper level support remaining well north of the
region today, frontogenetic forcing is expected to produce only a
thin band of showers with an isolated thunderstorm or two along
the front. Best rain coverage along the front today will be
relegated to areas with greatest moisture; based on trends in the
GOES-16 total precipitable water imagery this appears to be
across the Brazos Valley (1.4-1.6" PWATs). Interestingly, the
coastal waters may end up seeing the most rain out of the entire
forecast area today as a plume of 1.8-2" PWATs moves into NW Gulf,
but this is expected to remain relegated to the waters before the
front sweeps off the coast. Rain chances will end northwest to
southeast behind the front today, with a tight surface pressure
gradient behind the front resulting in northerly winds increasing
into the 10-20 MPH range. Stronger winds are expected along the
coast and a brief wind advisory may be needed tonight for
immediate coastal areas as northerly winds may climb as high as
20-30 MPH.

Clearing skies and cold air advection behind the front will allow
for temperatures to fall into the 50s north of Interstate 10
tonight with low to mid 60s elsewhere. Dry northwest flow aloft
becomes established by Monday and persists into Tuesday, keeping
rain chances nil with temperatures below seasonal normals. Expect
highs in the mid 70s to near 80 and lows in the upper 40s to mid
50s inland, upper 50s to low 60s along the coast.

Shortwave ridging aloft builds across the region Wednesday into
Thursday ahead of an amplifying shortwave trough over the Southern
Plains, allowing for temperatures to rise back to near seasonal
normals. Rain chances enter the forecast again by Friday and
continue through the upcoming weekend as return flow resumes and
remnant energy from the aforementioned shortwave trough lingers
over Texas.

Huffman

MARINE...
Light onshore winds will become northeasterly by mid morning out
ahead of the approaching cold front. Wind speeds will pick up
shortly after sunrise, remaining between 10-15 kts over the
coastal and offshore waters Sunday afternoon. Still expecting the
cold front to reach the coast between late Sunday afternoon into
early evening. Small craft should exercise caution starting at 03Z
Monday over the coastal and offshore waters. Went ahead and
issued a Small Craft Advisory for the coastal and offshore waters
beginning at 06Z, as sustained winds are expected to reach
criteria between 20 to 25 knots with seas between 5 to 7 feet.
Small craft should exercise caution in both Matagorda and
Galveston Bays starting at 06Z as well.

By Monday afternoon, northeasterly winds will slowly weaken, and
seas should lower to 2 to 4 feet by late Tuesday. Easterly winds
are expected to prevail by Wednesday, and wind speeds will once
again begin to increase. A long easterly fetch will set up across
the Gulf of Mexico Thursday, and remain through the weekend. Seas
will reach at least 5 feet by Thursday afternoon. Therefore,
elevated seas and tides will be possible late next week.

Currently, tides are running a little over a foot above MLLW.

Hathaway

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      81  55  77  50  78 /  20   0   0   0   0
Houston (IAH)              88  60  78  53  79 /  10  10  10   0   0
Galveston (GLS)            86  67  78  62  79 /  20  10  10   0   0

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...Small Craft Advisory from 7 PM this evening to 7 AM CDT Monday
     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...
     Matagorda Bay...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...99
Aviation/Marine...33



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