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FXUS64 KHGX 171124
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
524 AM CST Sat Nov 17 2018

.AVIATION [12Z TAF Issuance]...

Generally VFR around the area, though IFR/LIFR fog has cropped up
at Angleton. Given high cloud cover, am going a bit conservative
and sticking with 1SM visibility at 12Z rather than the 1/2SM
currently observed. But...this may not be aggressive enough.

Otherwise, looking for VFR to persist (or return when fog
dissolves) through the day with winds becoming SE 5-10 knots.
However, clouds at MVFR heights are expected to develop, then
eventually become ceilings late tonight. Rain chances won't be
picking up until after the forecast period, but do hint at what's
to come in the extended at IAH with a PROB30, and may indicate
potential if rains start up a bit early.

&&

.PREV DISCUSSION /Issued 407 AM CST Sat Nov 17 2018/...

.DISCUSSION...

In short, get outside today and enjoy the near normal
temperatures. Below normal temperatures will return behind a cold
front on Sunday and persist through Thanksgiving with a return to
near normal temperatures by the end of the holiday week. Rain
chances look highest in the Sunday/Monday time frame with the
front and coastal trough development and again Wednesday with
another upper level trough and coastal trough system.


.NEAR TERM [Through Today]...

Temperatures this morning range from the low 40s to the low 50s
with a solid deck of cirrus. Combination of high clouds and very
light southerly winds will limit radiational cool the rest of the
morning. There may be some patchy fog in the usual rural areas.
Surface analysis has the cold front pushing into the TX/OK
Panhandle/SW Kansas. High pressure has moved east so southerly
winds will continue ahead of the front today with some moisture
advection.

Looking aloft at the upper levels of the atmosphere, southern
branch of the jet continues across the southern U.S. with a ridge
out west and broad troughing over the northern tier states. There
was a good shortwave over the Inter-mountain West that should
continue to track SE towards the Rockies.

Overall there are not really any forecast concerns for today other
than to monitor high temperatures for the low 70s.


.SHORT TERM [Sunday Through Monday]...

Main changes to the forecast in the Sunday to Monday time frame
is for better timing of the cold front and then increased rain
chances. Based on upstream sounding analysis and then comparing to
several model sounding data, the airmass coming south should be
fairly shallow when it arrives in SE Texas on Sunday. The NAM 3km
nest, WRF ARW/NMM and Texas Tech WRF all seem to have a better
handle on the front than the other models. A blend of these models
was used to establish temperature trends for Sunday both ahead of
and behind the front. Ideally I would like to use the higher
resolution models for the temps behind the front and the more
synoptic models for temperatures ahead of the front. There very
well could be a 10 degree temperature gradient across Harris
County on Sunday. Temperatures then stay in the 50s for most of
the area on Monday with cloud cover and rain chances expected.

Rain chances increase from west to east on Sunday as the front
slides into the region and meets up with decent moisture advection
ahead of it. Shallow front may also support elevated convection
although most unstable CAPE values are not all that great. Model
sounding still show some decent lapse rates aloft so cannot rule
out some thunderstorms along the coast. Higher rain chances hold
on for Monday as the aforementioned shortwave in the Rockies
shears out over the Plains and a jet streak with its right
entrance region over the area moves east late Monday. There may
also be a left exit region moving over the NW Gulf on Monday with
that southern jet branch. In the end this should support some
coastal trough/low development and then isentropic lift over the
frontal surface for higher rain chances mainly along the coast for
Monday. Rain chances decrease from south to north across the
area.

Overall do not see a severe weather threat or heavy rainfall
threat although there could be some areawide 1 inch rainfall
amounts for the two day period. This should not cause any flooding
problems but may see some localized ponding of water on streets
or typical low lying areas.

Overpeck


.LONG TERM [Tuesday Through Saturday]...

Let's be honest the only time frame of the forecast that anyone
cares about is the day before Thanksgiving and Thanksgiving. And
I'm sure folks are wondering about that severe weather/flood
event on a holiday jinx/curse that we seem to be stuck in for SE
Texas. Wednesday into Thursday still looks wet but for the most
part narrowed down to Wednesday and Wednesday night. Thanksgiving
day does not look that bad since that is when the upper level
trough will be moving out of the area. This could have some travel
impacts for the area so you do want to pay attention to the
forecast and plan accordingly how to get to grandma's house.

Upper low west of the current ridge over the Pacific looks to
undercut this ridge Tuesday and move into Texas on Wednesday.
There is a pretty good jet streak following it that increases NW
flow aloft Wednesday night. Large scale ascent should be at its
peak over the area basically from Wednesday afternoon through
Wednesday night. The ECMWF seems to be a touch faster with this
system than the GFS and timing issues are to be expected since
this system is coming from the Pacific. Overall we still think the
main coastal low that forms should remain offshore but the GFS is
trying to be a pain and brings the warm sector airmass just inland
late Wednesday. The ECMWF keeps the coastal low and warm sector
offshore and thank goodness because that is where the ECMWF
produces a bullseye of 4-5 inches in 6 hours. Overall given the
isentropic lift and meager elevated instability, we still think
the area could get another 1-2 inches of rain with this event on
top of the 1 inch of rain expected earlier in the week. At this
time it is hard to say if any antecedent conditions will play a
role in the flood potential but certainly something to keep in
mind doing the forecast next week. Rain chances should end quickly
Thursday morning and that is even with the slower GFS.

Temperatures for the week should stay below normal given the cold
airmass that moves into the area to start the week. Cloud cover
and rain should keep the airmass from modifying much. Temperatures
do increase for the end of the week closer to normal since the
series of short wave troughs will come to an end with zonal flow.

Overpeck


.MARINE...

Winds are becoming southeasterly over the waters tonight as high
pressure moves off to the east. These winds remain light, and
resulting seas are low. However, as a coastal trough develops by
Sunday morning, look for winds to continue to back more towards
easterly and rain chances will increase.

A cold front moves into the area Sunday, but is expected to slow
down as it approaches the coast, and does not look to push offshore
until Monday. Once the front moves through, winds look to become
more northeasterly, and will become moderate to strong towards the
midweek.

Water temperatures around the area range from the upper 50s to lower
60s. With dewpoints rising to around or above 60 degrees today, then
into the lower half of the 60s Sunday, we may have to keep an eye
out for a low potential for sea fog. A favorable indication though,
is that the Galveston Bay Entrance water temp has risen from 60 to
63 degrees in the past 24 hours. If waters can continue to warm,
this will mitigate any fog threat. Regardless, this stands as a
reminder that sea fog season is upon us - if not now, it won't be
terribly long...

Tides will remain around their astronomical norms into the weekend.
As winds become more easterly/northeasterly and stronger, it would
be reasonable to expect a drift above those normals into the
midweek, though model guidance does not yet strongly indicate this.

Luchs

&&

.PRELIMINARY POINT TEMPS/POPS...

College Station (CLL) 71 54 55 43 52 / 0 20 50 40 50
Houston (IAH) 71 58 65 48 56 / 0 10 40 40 50
Galveston (GLS) 69 65 69 56 62 / 0 10 30 40 60

&&

.HGX WATCHES/WARNINGS/ADVISORIES...

TX...None.
GM...None.

&&

$$

NEAR TERM...Overpeck
SHORT TERM...Overpeck
LONG TERM...Overpeck
AVIATION...Luchs
MARINE...Luchs
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