Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 171742
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1142 AM CST Fri Feb 17 2017

.AVIATION.../18Z TAF/
Water vapor imagery shows one last vorticity maximum rotating
through the base of the upper low over north Texas. This has
allowed for a second round of convection to form along the coast,
some of the storms becoming strong. TAFs this afternoon will keep
a mention of SHRA/TSRA down along the coast with SHRA for Houston
terminals. Showers should be clearing out of the area after 21Z
this afternoon.

Models have some clearing through the evening which looks
reasonable given satellite trends. Models then show ceilings
dropping with a decrease in visibility. TAFs mostly have MVFR
ceilings and visibility but have added TEMPO groups for possible
IFR conditions for a few hours. SREF probabilities show at least a
few hours of IFR in the morning. Conditions should improve to
MVFR/VFR late Saturday morning.

Overpeck

&&

.PREV DISCUSSION... /ISSUED 952 AM CST Fri Feb 17 2017/

DISCUSSION...
With the main batch of showers moving off to the E/NE (at present)
we are continuing to see additional development near the coast off
to the SW. Based on current trends, banking on this activity to re-
main generally over the coastal counties as it moves across during
the afternoon. The rest of the forecast for short-term looks good.
41

PREV DISCUSSION...  /ISSUED 359 AM CST Fri Feb 17 2017/

At 2 AM, surface high pressure was located over the eastern Gulf
of Mexico and a trough of low pressure was located over high
plains. A weak area of low pressure was noted at 850 mb in north
central Mexico but 850 moisture looked sparse. Moisture was deeper
at 700 mb and a 700 mb trough extended from the central Rockies
into northern Mexico. At 300 mb, a well defined upper low was
spinning near the Big Bend and this feature shows up very well in
water vapor imagery. Upper level diffluence was noted over East
Texas and the western Gulf. The upper low over the Big Bend will
move east today and lift will increase over the eastern half of SE
TX today.Pw values will increase to through the day and reach
about 1.30 inches near the coast. Radar is already showing precip
and much of the rain is evaporating before reaching the ground
since the lower levels of atmosphere remain very dry. It`ll
moisten up with time and rain will begin to reach the ground later
this morning. Not sure how far rain will move inland today but
the higher rain chances will be near the coast and maybe a tier of
counties inland. Further inland, just expecting cloudy skies and
maybe a sprinkle.

Saturday looks nice with SE TX between high pressure to the east
and low pressure out west. There could could be some morning fog
and added patchy fog to the grids. 850 mb temps support sfc temps
in the lower 80`s with morning clouds giving way to aftn
sunshine. Not as clear cut on Sunday as fcst soundings show PW
values increasing to 1.50 inches during the afternoon and clouds
hanging around for much of the day. GFS and NAM both support
shra/tsra developing in the late afternoon and have raised PoPs
for the central and western zones. Temps are a bit tricky as
clouds and rain could keep temps lower than currently fcst, but
considering the warm start to the day, even nominal heating should
bump the temp to near 80. The SREF ensemble shows some potential
for sea fog near Galveston Bay and the Gulf waters off of
Galveston. Have added patchy fog to marine zones for Sat night
into Sun morning.

Made a few changes to the previous forecast and increased PoPs
for Sunday night as models want to speed the next system up. There
are some timing differences between the GFS and the slower ECMWF
and Canadian. PW values will increase to around 1.80 inches and
fcst soundings look saturated from the sfc to 300 mb. Upper level
winds split over SE TX and the region will lie in a 300 mb jet
couplet. Have increased rain chances Sunday night to 80 percent.
There will be some heavy rain but the system is looking more
progressive with each new model run so not quite ready to add
heavy rain to the grids. FWIW, WPC has placed SE TX in a marginal
risk for excessive rain for Day 3. The rain will likely linger
into Monday but the GFS dries things out pretty quick with PW
values falling to 1.40 inches by noon and to 1.13 inches by 00z.
The ECMWf/Can are slower but still progressive. Can`t completely
ignore the timing differences so have carried higher PoPs into
Monday afternoon but confidence is not terribly high for the rain
to continue through Monday aftn.

Rest of the week ahead looks quiet with dry conditions with above
normal temperatures though the end of the week. 43

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      72  57  82  62  80 /  30  10  10  10  40
Houston (IAH)              70  57  82  63  80 /  50  10  10  10  30
Galveston (GLS)            67  63  73  66  73 /  70  10  10  10  20

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...NONE.
&&

$$

Discussion...41
Aviation/Marine...39



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