Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 191144 CCA
AFDHGX

Area Forecast Discussion...CORRECTED
National Weather Service Houston/Galveston TX
544 AM CST Sun Feb 19 2017

.AVIATION...
Difficult and complicated forecast for the terminal sites over the
next 24 hours. Confidence levels are best for the first 6 to 12
hours.

For the first 6 hours, LIFR/IFR should lift to at least MVFR by
around 15Z and then VFR between 15Z and 18Z. Radar showed some
potential for light rain or drizzle at 1130Z but the chances were
too low to mention at this time. With the ceilings lifting late
this morning, wind speeds will pick up and some inland sites may
experience gusts between 20 and 25 knots.

MVFR to IFR/LIFR expected to return this evening. Models then
differed on the timing of showers and thunderstorms during the
overnight period. The GFS and Texas Tech 3km WRF were the faster
of the models and took at blend of both. Good chance that the low
ceilings will lift as the storms arrive between 08Z and 12Z.

There are indications that periods of thunderstorms could last at
least from 6 to 12 hours on Monday. Planning should include the
possibilities of localized flooding and isolated strong
thunderstorms.

40

&&

.PREV DISCUSSION... /ISSUED 351 AM CST Sun Feb 19 2017/

DISCUSSION...
Patchy fog and low clouds prevail early this morning. The fog is
expected to dissipate by mid morning but skies will remain
generally cloudy through the day. Could be a light sprinkle or
some drizzle this morning beneath a strong capping inversion. 850
temps remain very warm and considering the warm start to the day,
it won`t take much heating to boost high temps to 80. Limiting
factors would be the cloud cover and stronger winds. Trimmed PoPs
for today as ascent from the approaching upper trough won`t arrive
until tonight and fcst soundings show relatively dry moisture
profiles and a capping inversion in place for most of the day.

Moisture increase rapidly tonight as an upper level trough
approaches West Texas. PW values reach 1.5-1.6 inches by 09z and
1.80 inches by 12z. Fcst soundings show a saturated profile from
the sfc to 500 mb at 12z over the central/coastal zones. The GFS
dries things out over the west with very dry air moving into the
900-700 mb layer at 12z which considering the dynamics and
orientation of the moisture axis, well, it looks weird. The GFS
fcst soundings tries to dry things out quickly on Monday but with
the upper level trough axis to the west, shra/tsra likely to
persist into the mid afternoon before drying commences. The TT WRF
which performed very well on Friday maintains rain all day
Monday. Upper level winds still look very favorable as SE TX will
lie in a splitting jet at 300 mb and will also lie in a weak jet
couplet. Have added locally heavy rain to the weather grids. At
this time, it appears widespread rainfall of 1 to 2 inches with
isolated totals between 3 and 5 inches will fall across the area.
SPC has placed the western half of SE TX in a marginal risk for
severe weather for late tonight. Could get some gusty winds and
small hail but it appears the primary hazard will be heavy rain.

Drier air will work into the region Mon night and Tuesday as weak
high pressure moves into the state behind the departing upper
trough. Temperatures will remain unseasonably warm with highs in
the mid/upper 70s. Unseasonably warm temps will prevail for much
of next week as 850 temps stay warm. The air mass will be dry so
there should be a relatively large diurnal range each day. Low
pressure will develop in the lee of the Rockies on Thursday and
this system will move northeast and drag a cold front across SE TX
Friday evening. Might have enough moisture to squeeze out a
shower or two but will keep the fcst dry for now. Temps will trend
cooler next Saturday in the wake of the front. Warm air advection
next Sunday will bring a few showers and slightly warmer temps
back to the area. 43

MARINE...
Will keep the marine dense fog advisory through 10:00 AM over
Galveston Bay and from 0 to 20 nm offshore east of Freeport.

Patchy areas of sea fog, some dense, will continue to affect the
Gulf waters within 20 nm of the coast mainly east of Freeport and
also over Galveston Bay. There have been some indications of patchy
sea fog west of Freeport and over Matagorda Bay but do not think (at
this time) that the fog will become dense. However, will continue to
watch the observations and may need to expand the current marine
dense fog advisory if needed.

The models have backed off a bit on the wind speeds over the marine
areas later today. Still think at least caution conditions will
develop over the Gulf waters mainly between 20 and 60 nm offshore of
the coast this evening.

As the main storm system moves into the upper Texas coastal areas,
am expecting widespread rain and thunderstorms to occur tonight and
Monday. Conditions should improve Monday night and Tuesday and even
though offshore winds will develop, the potential for the strongest
winds will be on Monday and Monday night.

40

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      80  65  72  57  76 /  30  90  80  20  10
Houston (IAH)              80  67  72  60  75 /  10  80  90  30  30
Galveston (GLS)            74  67  70  63  72 /  10  60  90  40  30

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...Dense Fog Advisory until 10 AM CST this morning for the
     following zones: Coastal waters from High Island to
     Freeport out 20 NM...Galveston Bay.

&&

$$

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



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