Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 150513
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1113 PM CST Sun Jan 14 2018

.AVIATION...
Clear skies are expected this evening but have some concerns that
some shallow patchy ground fog could develop around sunrise.
Clouds will be on the increase on Monday with a BKN-OVC deck
possible by mid afternoon. Short range guidance hints at some
weak warm air advection showers over the W-SW zones Monday
afternoon. Will not mention showers at this time. However a cold
front will approach the area late Monday night and will introduce
rain chances between 03-06z across the NW zones. Temperatures
will remain above freezing through 06z so will carry rain at this
time. Winds will become north and increase in the wake of the
front. 43

&&

.PREV DISCUSSION... /ISSUED 939 PM CST Sun Jan 14 2018/

UPDATE...
East to southeast winds tonight have allowed for slow recovery of
dew points, with this limited moisture return and good
radiational cooling conditions promoting some patchy fog
development southwest of the Houston metro closer to sunrise.
Moisture return will also keep temperatures from free falling out
of the 30s tonight, but given hourly trends running a few degrees
cooler than forecast have lowered overnight lows a few degrees
into the lower to mid 30s inland and mid 30s to low 40s along the
coast. Warm air advection sets up during the day Tuesday ahead of
a strong cold front and a few streamer showers will be possible
across the southwestern counties/around Matagorda Bay as a result.

For the Monday night through Tuesday night portion of the
forecast, have held off on issuing any Winter Storm Watches.
Travel impacts will be possible as overrunning precipitation
behind a cold front early Tuesday morning transitions from
rain/freezing rain to sleet (and possibly snow) through the day
Tuesday, but forecasted accumulations do not support Watch
issuance at this time. However, a Winter Weather Advisory will
likely be needed for all or portions of Southeast Texas during
this time.

Huffman

PREV DISCUSSION... /ISSUED 354 PM CST Sun Jan 14 2018/

DISCUSSION...

Tonight through Wednesday...
Cool but benign weather is expected through Monday. A strong cold
front will push through the area early Tuesday morning with
periods of rain beginning overnight Monday night. Temperatures
will fall throughout the day on Tuesday with the rain gradually
changing over to a wintry mix starting early Tuesday morning
across the Brazos Valley and Piney Woods region. The change over
to a wintry mix will gradually work its way southward throughout
the day on Tuesday, even approaching the coast by Tuesday night.
Light ice accumulations of under 0.1 inch will be possible area-
wide, but are more likely across the northern and western portions
of the area. Light snow accumulations are also possible across
the Brazos Valley and Piney Woods region. Forecast confidence
continues to increase, and we now have moderate to high confidence
of at least some wintery precipitation falling. The finer details
of precisely what type of mix, accumulations, and timing will
likely change some as we get closer to the event. A Winter Storm
Watch could be issued in the next day or so.

Cold temperatures are expected Tuesday night in the wake of the
front, with lows reaching the low/mid 20s inland and near freezing
at the coast. Any remaining water could freeze and create
additional ice issues. A Hard Freeze Warning may be required for
portions of the area. Temperatures should gradually warm through
the day Wednesday, eventually climbing into the upper 30s to low
40s during the afternoon. 11

Wednesday Night through Monday...
Onshore flow returns Wednesday night as the surface high pressure
system moves eastward over the Tennessee Valley. Isentropic
upglide takes place ahead of an upper-level shortwave trough that
will cross the area Thursday night. The big question is whether or
not the moisture and lift will align with the sub-freezing
temperatures early Thursday morning. At this time, a slight chance
for a wintry mix is possible along the northernmost counties
Thursday morning. Models have trended drier and colder, so
confidence at this time is low. If any wintry precipitation
occurs, accumulations and impacts should be minimal.

The shortwave trough will linger in the Gulf and develop a weak
surface low off the Texas coast, which will keep rain chances
along the coast and offshore throughout the day Friday. Otherwise,
the warming trend will continue until a cold front passes during
the day Sunday. 22

MARINE...
Light east winds over the bays/coastal waters will be slowly shifting
to the SE tonight/early tomorrow (as the high continues to move
off to the east). The return of light/moderate onshore winds is
expected to remain in place through Mon night/early Tues morning.
The return of low-level moisture could produce some isolated
showers by Mon afternoon.

However, the main forecast problem looks to be the very strong cold
front progged to move into the Gulf waters Tues morning.
Scattered or isolated showers will accompany its passage into the
region. Behind this front, strong offshore winds will be
developing. Have issued a Gale Watch for just the coastal waters
starting Tues afternoon thru early Weds morning...in anticipation
of frequent wind gusts at/near 35 knots. This strong arctic high
is then expected to drift through the southern states...helping to
maintain moderate/strong east flow across the offshore waters the
rest of the week. Rain chances could increase Thur/Fri as a
coastal surface low develops near the middle TX coast. 41

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      35  61  30  32  23 /   0  10  60  50  20
Houston (IAH)              36  62  40  41  27 /   0  10  30  50  30
Galveston (GLS)            42  58  47  48  32 /   0  10  30  50  40

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...Gale Watch from Tuesday afternoon through Wednesday morning 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...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...14
Aviation/Marine...43



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