Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 220115

Area Forecast Discussion
National Weather Service Houston/Galveston TX
715 PM CST Sat Jan 21 2017

Sharp low level inversion producing lots of ducting and AP on the
radar. Virga and a few showers moving through northern Hill
Country that will track east and across the northern TAF sites of
CLL/UTS and possibly CXO. Not likely that any significant impacts
will occur there. Further south is more problematic...fog. Area of
fog and very low cigs blanketed the area around Matagorda Bay and
was expanding up the coast. Expect 2-4 mi visby at GLS to lower as
this overspreads the area. Dense fog with visby 1/2 mile or less
certainly within the realm of reasonable possibility. LBX will
also have fog issues and but may be more patchy early this evening
then thickening after 02-3z. UA showing the nose of the mid/ll
jet core sweeping east through WTX/into Hill Country bulging out
the cold front with pressure falls across Brush Country. Cold
front will move quickly east tonight (CLL around 6z- 9z GLS) and
winds will increase noticeably with westerly flow of 15-20knots
and gusty. After heating gets started Sunday morning much stronger
LL jet axis marches in and winds ramp up to 20-25kts with gusts
30-45kts becoming more NW in the afternoon. Wrap around moisture
(3500-5000ft) could expand down from northern sites into CXO-IAH
mainly in the 14-21z timeframe. Not very confident it will get
that far south. Winds Sunday evening diminish inland and slowly do
so at the coast.


.PREV DISCUSSION... /ISSUED 409 PM CST Sat Jan 21 2017/

Jet core advancing north out of the Rio Grande and streaming
across south central state. This strengthened slightly veered
westerly flow...along with the low-mid level advection of a Valley
dry air mass...has cleared skies out to clear. Full sun to the
surface...with a westerly component to the surface wind field...has
allowed some locations in (and south-west) of the city to touch
the lower 80s. Generally a day in the middle to upper 70s with an
anticipated clear evening allowing temperatures to quickly fall
into the low to mid 60s shortly after sunset. Enhanced PVA with
lingering moisture ahead of a nearing cold frontal boundary keep
slight NE forecast area evening rain chances in place. Hirez models
show a 20-30 percent chance of -shra (possible rogue storm) to
clip the far northern counties. Sea fog just off the coast will
pull back to the shoreline in the coming hours...locally dense in
the evening as the region falls just downstream of an approaching
cold front.

The upper trough axis will be east of the region by 18Z Sunday...
with the associated cold frontal passage to occur from the early
overnight Sunday morning hours through the late morning hours.
Strong offshore winds in this front`s wake will reach advisory
criteria by 9 or 10 AM and maintain these magnitudes through
around this time tomorrow. Recent rain has saturated the ground
enough that shallow rooted trees may topple within these strong
daytime northerlies. Transitory ridging at all levels Monday will
weaken offshore winds with backing mid-upper flow drawing up a
warmer southwesterly air mass...85H temps will cool to the 4-5 C
range tomorrow afternoon during the brunt of the CAA and warm
back to around 16-17 C by Tuesday morning. Thus...after a relatively
cooler Sunday in the 60s and a Monday in the 70s...upper 70 to
lower 80 afternoons will be the theme Tuesday. A weak cold frontal
passage early Wednesday will regulate warming to the low to mid
60s once again. Slight rain chances will be painted across the SE
forecast area/Gulf Wednesday just ahead (or along) the boundary
as it travels offshore by Wednesday noon.

Mid to late week weak upper troughing over the MS River Valley...
with surface ridging enveloping the state...has northeast winds
veering to east through Friday. A relatively dry and cold frontal
passage slated for early Saturday will allow an arctic based
chilled air mass to spill into the region over the weekend.
Subfreezing mid-level air reaching the coast Saturday night will
lower overnight (weekend) minimums to under 40 F. There are slight
POPs in place early Saturday and...depending on the arrival of the
coldest lower-middle layer air in relation to the highest downstream
moisture...the mention of frozen precipitation may work its way
into future forecasts. 31

A light to moderate southwest flow will persist through the early
evening before wins decrease ahead of a cold front. As winds
decrease, there will be a brief window for fog to develop near
Galveston Bay. The front is expected to cross the coastal waters
between midnight and 3 AM. Moderate to strong west winds will develop
and increase in speed toward sunrise. A Gale Warning has already
been hoisted for all waters and see no reason to reconfigure at this
time. The Gale Warning will expire at 03z Monday but some refinement
will be needed Sunday aftn to drop the bays.

The W-NW component to the winds will drive water out of Galveston
Bay and low water is expected at Morgans Pt and Manchester on
Sunday. Although tide levels are running about a foot above normal
today, the sustained west wind will quickly lower tide levels to
about a foot below normal by Sunday morning and possibly 1.5 to 2.5
feet below normal by Sunday afternoon. A Low Water Advisory has been
issued for Galveston Bay from 12z Sunday through 00z Monday.

Winds and seas should slowly diminish Sunday night into Monday,
becoming onshore Monday night and strengthen through Tuesday.
SCEC and possible SCA conds may be required Tuesday. Another cold
front will cross the coastal waters on Wednesday with offshore
winds prevailing through next weekend. 43

A strong cold front will cross SE Texas tonight. Strong west to
northwest will develop in the wake of the front and remain strong
and gusty through Sunday. Recent rains have left fuels wet but
significant drying is expected early Sunday as winds increase and RH
values drop. Min RH values are likely to range between 30 and 40
percent but grasses and other fine fuels will dry quickly in the
wind. Elevated fire weather conditions are likely on Sunday but the
antecedent wet conditions coupled with RH preclude a Fire Weather
Watch or Red Flag Warning at this time. RH values on Monday look
lower but wind speeds will be significantly lighter. 43


College Station (CLL)      50  67  44  74  51 /  30   0   0   0   0
Houston (IAH)              54  69  47  73  52 /  20   0   0   0   0
Galveston (GLS)            57  67  53  69  59 /  20   0   0   0   0


TX...Wind Advisory from 9 AM to 5 PM CST Sunday for the following
     zones: Austin...Brazoria...Brazos...Burleson...Chambers...
     Colorado...Fort Bend...Galveston...Grimes...Harris...
     Montgomery...Polk...San Jacinto...Trinity...Walker...

GM...Gale Warning from 2 AM to 9 PM CST Sunday 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.



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