Area Forecast Discussion
Issued by NWS Houston/Galveston, TX
FXUS64 KHGX 231120
Area Forecast Discussion
National Weather Service Houston/Galveston TX
520 AM CST Mon Jan 23 2017
.AVIATION [12Z TAF Issuance]...
Winds are coming down, leaving a very quiescent forecast period
across SE Texas. The main forecast issue will be timing the shift
of light winds from northwesterly to more or less southerly. This
shift seems to have already begun, but is likely to take until
tomorrow morning to complete.
As high pressure settles into the region tonight, there will
certainly be the light winds and clear skies needed for radiation
fog, but getting enough moisture in place by tonight is very
questionable. Forecast soundings are pretty dry, but starting to
indicate shallow surface moisture towards morning. Right now not
enough confidence to reduce visibility at all, but may be
something to watch for.
.PREV DISCUSSION /Issued 404 AM CST Mon Jan 23 2017/...
.NEAR TERM [Through Today]...
Surface analysis this morning shows low pressure over the
Carolinas and high pressure over Texas. Pressure gradient from
this system has moved east allowing winds to relax this morning.
Yesterday most areas had 25 to 35 mph winds with wind gusts 40 to
50 mph. Winds today will be a lot less with high pressure building
over the area. Look for high temperatures today to reach the upper
60s to low 70s across the area.
Upper level pattern remains progressive with analysis showing the
stacked upper low over the Carolinas with another upper low off
the coast of the Pacific NW. Ridging aloft will be building over
the Plains today. Ridge will be moving east today and tomorrow as
the upper low moves down towards the Desert SW on Tuesday allowing
for SW flow aloft over Texas.
.SHORT TERM [Tonight Through Wednesday]...
Tuesday is on track to be a rather warm day. One shortwave trough
moves into the plains allowing for cyclogenesis in the plains and
warm air advection over SE Texas with return flow. Temperatures at
850mb increase to around 14C to 17C with SW LLJ of 40-50kts. With
this in mind, high temperatures in the low 80s look reasonable and
will be a degree or two from tying record high temperatures for
the day. Galveston and Houston IAH will be the locations record
will have the high chance to be broken.
This thermal ridge at 850mb over much of SE Texas also support a
decent capping inversion from the elevated mixed layer. Going into
Wednesday, a cold front should move into the area early in the
morning. Boundary layer moisture should be enough to support a
weak line of showers, but given the capping will leave out mention
of thunderstorms. Model soundings do not show too much instability
to work with even if the cap erodes enough. In addition, the jet
streak right entrance region will be slow to provide lift as it
moves by late Wednesday. Temperatures behind the front will be
about 10 to 15 degrees lower than on Tuesday and the airmass
should be plenty cold behind the front to keep temperatures near
normal for the end of the week.
.LONG TERM [Wednesday Night Through Monday]...
Upper level pattern remains progressive for the end of the week
with a second short wave moving across Texas Wednesday night into
Thursday and ridging builds over the Pacific NW. A broad long wave
trough develops from east of Hudson Bay through the Great Lakes. A
short wave trough over the Great Basin then cuts off over the
weekend with a short wave trough axis rotating through the mean
flow of the long wave trough in the Midwest. This pattern allows
for another cold frontal push Saturday with mainly just a re-
enforcing shot of cold air. Return flow sets up again next Tuesday
with another possible front next Wednesday. Moisture return seems
to be lacking ahead of each of these fronts so not expecting any
rain chances. The re-enforcing of the polar airmass will help keep
temperatures near normal for the end of January.
Gusty winds from Sunday continue to ease down tonight, but winds
over the nearshore waters, particularly off of Galveston Bay,
haven`t come down quite as much as anticipated, and will have to
extend the small craft advisory into this morning. Winds will
continue to diminish today as high pressure settles into the region.
This period should be rather brief, as a new low pressure system
looks to form in the lee of the Rockies, and we can expect winds to
turn onshore and strengthen as the developing low tightens the
pressure gradient. As the low moves on, expect its trailing cold
front to cross the area Wednesday, reversing flow again. At least
SCEC conditions are probable both on Tuesday and behind the front
Wednesday night, with Small Craft advisories potentially needed. The
best shot for a small craft would be Wednesday night in the offshore
After the front passes, either offshore winds or shore-parallel
northeasterly winds should dominate through the weekend. A brief
exception may come Friday, when winds may acquire enough of an
easterly component to restore some type of onshore connection.
However, those winds will become northwesterly again on Saturday
with the arrival of another front.
Moderate to strong W-NW winds will persist over the Gulf waters
tonight and slowly decrease after midnight. Will maintain the Gale
Warning over the Gulf waters but change the Bays to a Small Craft
Advisory as winds are expected to decrease very early this evening.
Considerably lighter W-NW winds are expected Monday as weak high
pressure settles over South Texas. Low pressure will develop in the lee
of the Rockies on Monday night and the pressure gradient will begin to
tighten. The onshore flow will increase on Tuesday. Lighter winds expected
on Tuesday night in advance of a cold front. The cold front will cross
the coastal waters early Wednesday with an offshore flow developing in
the wake of the front. Offshore winds expected through Thursday as high
pressure settles over Central Texas. Surface high pressure moves east on
Thursday night and sfc winds will become easterly through Friday night.
Another front will cross the coastal waters early Saturday. SCA conditions
possible behind the front next Saturday.
Water levels have been slow to recover tonight, and remain 1.5 to 2
feet below normal tonight. With winds continuing to relax, this
should improve through the day and return to more typical levels,
particularly later in the afternoon once winds begin to back and
become more westerly.
Some fire weather concerns will remain today, following
yesterday`s short fuse red flag warning due to very gusty winds
and near critical humidity. Indeed, relative humidity looks to be
marginally lower, with the same problem areas well southwest of
Houston dipping below 30 percent again, while most of Southeast
Texas falls into the 30-35 percent range. Fortunately, winds
should be much lower, mainly in the 5-10 mph range with an
occasional gust near or a little above 15 mph. ERC values remain
below the 50th percentile, though the low RH likely means an
outsize influence from wetter heavy fuels, while grassy fuels
will respond more to the second consecutive day of low humidity.
These lighter winds have forecast fire danger from TFS easing back
into the low-moderate range across the area.
.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 69 52 80 50 65 / 0 0 10 10 10
Houston (IAH) 70 52 81 59 70 / 0 0 10 20 10
Galveston (GLS) 68 62 76 62 70 / 0 0 10 20 20
GM...Small Craft Advisory until 6 AM CST early this 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.
Small Craft Advisory until 8 AM CST this morning for the
following zones: Waters from Freeport to the Matagorda Ship
Channel from 20 to 60 NM...Waters from High Island to
Freeport from 20 to 60 NM.