Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 181140
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
540 AM CST Sat Feb 18 2017

.AVIATION...
The model forecast soundings showed the low-level inversion nicely
at 11Z. Moisture under the inversion has led to LIFR to MVFR
across the area terminals. Expect that best chances for patchy
dense fog will occur from KCLL to KSGR and KLBX through around
14Z. All of the inland sites will likely only see a gradual
improvement to overall MVFR by 15Z.

Model data shows marked improvement between 17Z and 18Z when the
low-level inversion breaks. This will lead to VFR conditions but
with some breezy conditions at the surface due to mixing.

At the coast, KGLS may see more breaks by mid morning; however,
developing sea fog is expected later today and probably between
23Z and 03Z. The sea fog may work its way inland to KLBX by 04Z.
Elsewhere, expect MVFR to LIFR conditions to develop by around 06Z
as the low-level inversion becomes re-established.

40

&&

.PREV DISCUSSION... /ISSUED 333 AM CST Sat Feb 18 2017/

DISCUSSION...
At 2 AM, weak low pressure was located over north central Texas
with high pressure over the eastern Gulf of Mexico. Fog has
developed and and some of the fog has gotten dense with visibility
down to a 1/4 mile at PSX and BYY. The Dense Fog Advisory in
effect for the SW zones may need to be expanded north prior to
sunrise. The fog should burn off between 9-10 AM with skies
quickly becoming mostly sunny. 850 mb temps have warmed and
considering a slightly warmer start to the day and expected
sunshine, aftn temps should warm into the lower 80s. Clouds are
expected to redevelop this evening and this will likely inhibit
much of a temperature drop overnight. Winds don`t look like they
fully decouple either so expecting overnight min temps to remain
very warm.

Sunday will start out warm and there will likely be some
intermittent sea fog near Galveston as sfc dew pts will be in the
mid/upper 60s and water temps remain in the lower 60s. The threat
for sea fog will persist through Sunday night. Further inland,
deeper moisture will be drawn into SE TX as a deep upper trough
off the west coast begins to move east. The system continues to
look progressive and by Sunday afternoon, the trough axis will
extend from central CO into southern NM. Skies will become mostly
cloudy and it will also become breezy. Warming temps at 850
suggest very warm temps to continue but with the extensive cloud
cover and mixing from stronger winds, feel max temps might be a
few degrees cooler than Saturday. Fcst soundings also show
convective temps between 79-81, weak capping that looks like it
can be broken and overall a profile that looks unstable with CAPE
over 2000 j/kg and LI values of -8. SPC has areas west of I45
outlooked in marginal risk. Think the higher threat for severe
weather will remain further west but could impact the College
Station/Brenham areas late in the aftn.

The upper level trough axis moves east Sunday night and numerous
shra/tsra are expected across SE TX. PW values increase to between
1.60 and 1.80 inches. 850 mb winds will be around 35-40 kts with a
hint of some 850 wind convergence around 12z Monday. Storm motion
should be pretty quick with these storms but there could be some
training of storms between 09-15z Monday. Jet dynamics look
impressive with this system and SE TX will lie in a well defined
split in the jet and also lie in a RRQ of a departing 120 speed
max. All in all, a pretty good set up for widespread rain, and
some of the rain will be locally heavy. The storm motion and the
speed of the upper level trough will probably spare much of the
area from excessive rain but there will be some pockets of heavier
rain possible due to the high PW values and strong jet dynamics.

The system will continue to move east and drying should begin
late Monday afternoon as PW values drop to 1.2-1.3 inches by late
afternoon. A weak area of high pressure will build into the Ozark
plateau Tues/Wed with generally clear skies and above normal
temps. Low pressure will develop over the central plains on
Thursday and the low will move NE on Thursday night and drag a
cold front across SE TX early Friday. At this time, it looks as
though the front will remain dry and no precip is expected along
the boundary. Cooler temps will filter into the region behind the
front for next weekend. 43

MARINE...
Surface moisture advection was leading to surface dewpoints of the
mid 60s moving over the cooler continental shelf waters just off of
the coast early this morning. Water temperatures ranged from about
62 to 63 on the coastline to about 63 go 65 20 nm offshore. The
water temperatures then increased to 70 about 60 nm offshore.
Southeasterly winds has lowered the fetch of higher moisture over a
more narrow cooler water area; so, have not noticed any sea fog
development as of 3:00 AM. However, a slow increase in the surface
moisture should lead to better chances for sea fog formation later
today -- most likely during the mid evening tonight through mid
morning tomorrow according to the statistical guidance and the SREF
probabilities, and the high resolution models such as the HRRR and
RAP13. The guidance and models are showing good chances even with
increasing wind speeds tonight and Sunday morning.

An increasing pressure gradient will then lead to increasing onshore
wind speeds, and expect at least SCEC conditions over the nearshore
and SCA over the offshore waters by Sunday afternoon. An approaching
storm system from the west will then help diminish the pressure
gradient leading to slightly weaker wind speeds Sunday night and
Monday. However, thunderstorm chances will return, including chances
for strong storms, Sunday night and Monday.

40

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      82  64  79  63  74 /  10  10  40  80  70
Houston (IAH)              82  66  79  67  74 /  10  10  30  80  80
Galveston (GLS)            73  66  72  66  71 /  10  10  20  70  80

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Dense Fog Advisory until 9 AM CST this morning for the following
     zones: Austin...Brazos...Burleson...Colorado...Jackson...
     Matagorda...Washington...Wharton.

GM...NONE.
&&

$$

Discussion...43
Aviation/Marine...40


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