Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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582
FXUS64 KHGX 151843
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1243 PM CST Sun Jan 15 2017

.UPDATE...
The forecast was strongly on track this morning, with temps that
tracked very close to forecast and scattered showers with a
thunderstorm or two. Of late, not only has fog dissipated, but
some breaks in the clouds have been seen, allowing for
temperatures to quickly jump into the middle 70s where the most
sun has been able to peek through. Additionally, showers have
become more numerous along a mesoscale boundary lifting into the
northern part of our area, and so have increased both PoPs across
the area and temps in the south. While the HRRR keeps the area
essentially dry in the wake of the northern showers and storms,
there is concern with offshore showers on radar, some favorable
jet placement, plenty of moisture, and potentially more
instability from higher than forecast temperatures. So have
instead opted to raise PoPs farther south rather than decrease
them as the model guidance might imply. Still, in deference to the
dry models, have kept them markedly lower than the likelies now
in place in the north.

Luchs

&&


.PREV DISCUSSION... /ISSUED 522 AM CST Sun Jan 15 2017/

AVIATION...
Showers moving in from the Gulf were helping to mix out the
airmass enough to lift the fog that had formed earlier in the
night. The ceilings are expected to lift enough for VFR at most
sites this afternoon. As this occurs, breezy winds gusting to
around 20 knots are likely. However, MVFR and lower conditions
will redevelop by or shortly after 00Z this evening. The higher
resolution models are showing better potential for low ceilings
over fog development.

40

PREV DISCUSSION... /ISSUED 341 AM CST Sun Jan 15 2017/

DISCUSSION...
At 07z...a weak front was located from just south of Lufkin to
south of College Station to just north of Hondo. The front is
progged to become diffuse with southeast winds returning by late
morning. Sea fog that has plagued the coast for the past couple of
days has dissipated as some rain showers over the Gulf moved
inland. Conditions still look favorable for sea fog today and will
continue to mention in the weather grids. Water temps have warmed
to 60 degrees and with winds veering to the SSE, the threat for
dense sea fog appears to be diminishing. The HRRR and SREF don`t
show much in the way of fog for the next 24 hours. As for the rest
of today, forecast soundings show a saturated layer from the
surface to 850 mb, so should get some streamer showers this
morning. Radar already showing some showers SW of Houston. By
afternoon, fcst soundings look a bit more unstable with a weak cap
eroding particularly over the western zones. Will add thunder to
the wx grids for the aftn. A deep upper level trough over the
western US will allow a series of short waves to move across SE TX
tonight through Thursday. The first s/wv will be ejected tonight
and move across the TX panhandle into central Kansas, This feature
coupled with slightly stronger jet dynamics will allow for
shra/tsra to develop tonight into Monday. Highest rain chances
should be over the WNW zones.

On Monday, another disturbance coupled with a weak cold front
approaching the region will keep rain chances in the forecast.
Fcst soundings show CAPE values near 1500 J/KG, modest shear and
strong low level lapse rates. SPC has maintained the Marginal Risk
for SE TX. Another short wave will drop into the base of the long
wave trough south of Baja and the s/wv will move east on Tuesday.
The front will move very slowly east across the CWA and serve as a
low level focus for shra/tsra. The front should get very close to
the coast and weak NNE sfc winds will develop behind the front with
some post frontal isentropic upglide possible Tues aftn. Another
short wave will move NE late Tuesday night into Wednesday and
bring much of Central and East Texas more rain. Fcst soundings
look saturated both Tues night and early Wednesday so a few spots
should get some locally heavy rain. There should be some limited
drying Wednesday afternoon as a brief period of subsidence in the
wake of the s/wv ensues.

The deep upper trough finally moves east Wednesday night and
Thursday. Jet dynamics look strong as the upper low moves east and
PW values climb back to near 1.50 inches. Another round of showers
and thunderstorms is expected to develop late Wed night into
Thursday. Finally some drying on Friday but more short wave
energy will approach from the west bringing a slight chance of
showers and thunderstorms both Saturday and Sunday. Temperatures
look to stay above normal through the period with a bit of a cool
down late next weekend. 43

MARINE...
The main issue for today and tonight will be fog chances. As of 2:30
AM, the fog had lifted across both Matagorda and Galveston Bays and
over the nearshore Gulf waters. As a result, the dense fog advisory
for the bays and nearshore waters have been canceled. The latest
SREF probabilities and the deterministic models (NAM12, HRRR, and
RAP13) only show the best potential over Galveston Bay through about
0600 this morning. Think that the potential will diminish throughout
the day as the winds become more southeasterly. SREF probabilities
show a small potential for dense fog redevelopment this evening. Two
factors should mean lower chances for dense fog development tonight
and Monday:  a more southeast to south-southeast wind flow and
mixing due to the development of scattered showers.

So, here is a summary for the next 48 hours:
- A break in the dense fog early this morning. Will monitor for
  any redevelopment and reissue a dense fog advisory if necessary.
- Patchy fog will be possible through the remainder of this morning.
- Possible fog redevelopment this evening but only low probabilities
  for any dense fog.

Winds off the coast will also increase to at least caution levels
this afternoon and tonight. A decrease in the winds are expected on
Monday. Along with the diminishing winds could mean the return of
sea fog; however, the winds will be more south to southwesterly
during the mid week period. Moderate onshore winds may return by the
end of the week over the Gulf waters.

40

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      72  64  74  55  63 /  60  60  70  60  50
Houston (IAH)              75  66  77  62  71 /  40  40  50  60  60
Galveston (GLS)            74  63  70  63  70 /  30  30  40  50  40

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION through Monday 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.

&&

$$

Discussion...25



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