Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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064
FXUS64 KHGX 081607
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1007 AM CST Thu Dec 8 2016

.DISCUSSION...
Latest trends in observations show temperatures slowly falling
across SE Texas this morning. Much of the area should remain in
the 40s with low 50s right along the coast. Windy conditions will
continue as will the wind advisory until 6PM. Wind chill values
will run in the 30s to low 40s for much of the day making it feel
colder. Rain chances should be decreasing through the day along
the coast but linger in the offshore waters.

As always determining freezing temperatures in SE Texas is a
challenge and this is no different. Couple of factors to consider.
First, cloud cover overnight which should be moving east. This
will depend upon how quickly a passing shortwave now over the Big
Bend moves across Texas. Second, winds should continue overnight
so there will not be much decoupling of the boundary layer if
any. Third, wet grounds from recent rains could keep the near
surface air warmer than if it were dry. This may be a very small
contribution. Finally cold air advection will be strong as 850mb
freezing line should reach KCLL to KLFK Friday morning.

We will evaluate 12z model guidance before tweaking the Min temp
forecast for Friday morning but really do not expect much change.
High confidence that areas from Brenham/Conroe/Cleveland will drop
below freezing. It will be the area between that line and
Columbus/Houston/Liberty that will be a challenge determining if a
freeze will occur. Be sure to know that we are only looking at the
outlying NW to N areas of Harris County that may experience a
brief freeze. The rest of the county will not but due to county
based hazards the whole county is in the freeze warning. Also with
any precipitation chances ending during the day due to drier air,
there will not be any chances of frozen precipitation tonight into
Friday morning.

Overpeck

&&

.PREV DISCUSSION... /ISSUED 528 AM CST Thu Dec 8 2016/

AVIATION...
Still a little light rain ongoing this morning and some patchy
light rain could still affect KSGR and KHOU but most TAF sites
will remain dry. Moisture trapped beneath a strong temperature
inversion will keep skies generally cloudy today. Clouds should
begin to thin/break out by late afternoon. Fcst soundings keep a
thin broken cloud layer around 8000 feet tonight. Winds will be a
concern as well with a tight pressure gradient in place. Added
gusts everywhere today with the higher sustained/gusts closer to
the coast. Winds do not fully decouple overnight. 43

PREV DISCUSSION... /ISSUED 451 AM CST Thu Dec 8 2016/

SHORT TERM (Today through Friday)...
Changes are on the way for Southeast Texas today as colder and
windy conditions become established in the wake of a strong cold
front. Increasing northerly winds across the area and surface
analysis indicate that this frontal boundary has cleared the Upper
Texas coast, with some weak 925-850 MB frontogenetic forcing
behind the front resulting in a few light showers along the
Highway 59 corridor this morning. Greater rain coverage was
occurring offshore where this morning`s front was colliding with a
remnant boundary south of Buoy 42019, with enough instability (low
level lapse rates around 5.5-6 C/km) to even produce a few
lightning strikes. Expect best rain chances to remain offshore
today as a result of the front`s passage, but with lingering weak
forcing behind the front cannot rule out a few stray showers
generally along and south of the Highway 59 corridor through the
day.

A stout pressure gradient behind the front early this morning
(change of 7 MB over approximately 140 miles) will persist through
most of the day as a 1040 MB surface high associated with the
front noses farther into the Southern Plains. As a result, expect
winds 20 to 30 MPH with stronger gusts approaching 35 MPH for many
areas near and just inland of the coast. A Wind Advisory remains
in effect from 6 AM to 6 PM CST. Have added Fort Bend and Wharton
counties based on latest short term guidance, but expect these
areas to experience frequent wind gusts above 25 MPH (as opposed
to sustained winds at 25 MPH, which is Wind Advisory criteria).
Winds will decrease by this evening as the pressure gradient
begins to relax with the surface high`s arrival.

Temperatures today will continue to fall for a few hours this
morning as cold air advection behind the front increases, but will
rise a few degrees or remain steady around lunchtime as cold air
advection is offset somewhat by daytime heating. Expect afternoon
temperatures in the low to mid 40s inland, with upper 40s to near
50 along the coast. Drier air filtering into the region behind the
front tonight will help clear or thin the low clouds across the
region, but still have concerns on how much clearing will occur,
with some lower level saturation (800-700 MB) continuing to be
advertised on soundings and relative humidity progs as far north
as a College Station to Livingston line. These clouds would help
inhibit (but not prevent) radiational cooling, keeping
temperatures warmer.

Additional concerns include the recent rainfall that parts of the
region have received (especially the 5 to 7 inches of rain that
Walker and Montgomery Counties got last weekend) and light
rainfall that fell yesterday, which would help keep the ground
warmer. Winds also appear to not entirely decouple tonight and
this would allow for enough mechanical mixing to occur to also
keep temperatures from completely bottoming out. With all these
concerns in mind, have bumped up overnight lows a degree or two.
However, given the strength of the cold air advection behind the
front even this adjustment results in widespread freezing
temperatures along and north of a Columbus to Tomball to Dayton
Lakes line. Have gone ahead and issued a Freeze Warning for Friday
from midnight to 9 AM CST for these areas.

Dry and chilly weather will greet the region during the day on
Friday, with highs in the mid 40s to low 50s under mostly sunny to
partly cloudy skies.

Huffman

LONG TERM (Friday Night through Wednesday)...
The expansive surface high over the Southern Plains in the wake
of Thursday`s front will gradually shift east of the region Friday
night. The associated weak pressure gradient across the region
will result in light easterly winds across most of the region.
This, combined with clearing skies over all but the southwestern
counties, will contribute to another cold night across the region
with many locations along and east of Interstate 45/ north of
Interstate 10 again dropping near to below freezing on Saturday
morning. It is quite possible a few locations in this area may
actually be colder than what they observe Friday morning as a
result of less cloud cover and lighter winds.

Temperatures will moderate quite nicely on Saturday, however, as
onshore flow and associated warm air advection allow highs to
climb into the 50s to low 60s. Cloud cover will also increase
throughout the day Saturday as moisture returns. Isolated to
scattered showers are forecast to spread into the western
counties Saturday night and expanding eastward across the area on
Sunday from a combination of isentropic upglide and warm air
advection. Temperatures will continue to warm on Sunday, with
highs climbing into the mid 60s to low 70s on Sunday. A weak
frontal boundary looks to make its way towards Southeast Texas on
Monday, but (with guidance continuing to trend towards a more
zonal flow aloft) have lower confidence this boundary will
progress through the region and instead expect it to wash out
somewhere across East Texas.

Medium range guidance continues to advertise a second front
moving into the region on Wednesday, but with (vastly) different
intensities. The GFS slams the front (and an associated 1045 MB
surface high/ much colder temperatures) into Texas early Wednesday
morning as an upper trough swings into the Central Plains, while
the European spreads the front and surface high farther north and
east (keeping temperatures warmer). The Canadian and a few of the
GFS ensemble members are more supportive of the European solution
and have kept the far extended portion of the forecast warmer.
However, none of these models are (yet) showing surface
cyclogenesis as this storm system approaches the Great Plains, and
this would help the cold air spread farther east (as opposed to
south, which is what the GFS is showing). Regardless, will need to
monitor the middle of next week for another shot of much colder
weather for Southeast Texas.

Huffman

MARINE...
A strong cold front has pushed through the coastal waters and
winds at Buoy 35 are already over 20 knots so moved up the start
time for the Gale Warning to the present time. Very strong N/NE
developing in the wake of the front will persist all day and into
the evening. Winds over the Gulf will frequently gust in excess of
40 knots. SCA conditions will prevail over the bays today/tonight.

There might be some impact on Thurs for the more north-to-south
ship channels as water is pushed out of the bays. The N/NE wind
direction is currently in the forecast...and not expecting any low
water advisories at this time.

The strong offshore flow will slowly decrease on Friday as the
surface high moves east. A moderate onshore flow is forecast for
Saturday...but winds will be increasing back to near SCEC/SCA
criteria for Sat night/Sun as the gradient tightens in response to
the next storm system moving across the Southern Plains. The next
front on Sunday night will probably stall inland and not reach the
coastal waters. Onshore winds will persist through Tuesday night
but speeds will drop off as the gradient weakens. Although there
are some timing differences between the GFS and ECMWF, it appears
that another cold front will cross the Gulf next Wednesday or
Thursday. 43

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      44  30  47  34  53 /  10   0   0  10  10
Houston (IAH)              49  33  49  33  55 /  10  10   0   0  10
Galveston (GLS)            55  41  51  45  61 /  30  10   0  10  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Freeze Warning from midnight tonight to 9 AM CST Friday for the
     following zones: Austin...Brazos...Burleson...Colorado...
     Grimes...Harris...Houston...Liberty...Madison...
     Montgomery...Polk...San Jacinto...Trinity...Walker...
     Waller...Washington.

     Wind Advisory until 6 PM CST this evening for the following
     zones: Brazoria...Chambers...Fort Bend...Galveston...
     Harris...Jackson...Matagorda...Wharton.

GM...Small Craft Advisory until midnight CST tonight for the
     following zones: Galveston Bay...Matagorda Bay.

     Gale Warning until midnight CST tonight 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...39



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