Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 231524
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1024 AM CDT Sat Sep 23 2017

.DISCUSSION...
12z sounding data from CRP/SHV support high temps near 90 this
afternoon so current temp forecast looks on track. Satellite
derived PW fields show higher moisture levels near Matagorda Bay
and other area of higher PW air over extreme East Texas.
Convective temps this morning are in the upper 80`s so feel
shra/tsra will increase in coverage with afternoon heating. Raised
PoPs to 30 percent near these two pockets of higher moisture.
Latest HRRR trends also support the slightly higher rain chances
this afternoon. Rest of the forecast looks on track so no other
changes planned at this time. 43

&&

.PREV DISCUSSION... /ISSUED 613 AM CDT Sat Sep 23 2017/

AVIATION...
A challenging night, and those challenges should be expected to
continue into today as there remains no new word on when the
issues with observations from the TAF sites might be resolved. IAH
and HOU have been augmented manually, which helps for those sites,
but this is not occurring at the other sites. Have appended AMD
NOT SKED to send the message that our ability to stay appraised of
conditions at the sites is not as high as normal. Will still
attempt to make amendments as other sources of data allow, but
this observation issue does pose difficulties.

Fog is developing tonight, and is starting to become dense west
of the area. So far, CLL has been just east of this more dense
patch, but with 11R and CFD in the neighborhood crashing, CLL may
follow shortly. Should see improvement to VFR shortly after the
open of the period, and is likely to continue until fog redevelops
late tonight. Onshore/Southeasterly flow can be expected again,
increasing to about 10 knots at a max this afternoon before
becoming light and variable again overnight.

Isolated to widely scattered showers should pop up across
Southeast Texas today, but with less coverage than even yesterday
expected, have opted to leave VCSH out of the TAFs for now. If a
more preferred area of development becomes apparent near a TAF
site, later cycles can address this.


PREV DISCUSSION... /ISSUED 401 AM CDT Sat Sep 23 2017/

DISCUSSION...
Normally I`d discuss current surface features and observations
but due to a communications issue observations from ASOS are not
being transmitted unless by an actual tower observer. This also
means we had to use early 1990s technology called a modem to dial
into the ASOS to get the daily climate report. We will also be
using that methodology to get updates on visibility across the
area. Fortunately we have a state of the art GOES 16 satellite to
help fill in the data holes especially for fog and low clouds.
Overall fog is patchy across the area but that could change over
the next couple of hours. We will of course be monitoring to issue
a dense fog advisory if obs indicate restricted visibility to a
quarter mile. Otherwise patchy fog should dissipate with the onset
of mixing through the boundary layer.

Looking at 00Z soundings precipitable water values around 1.8
inches at LCH and closer to 2 inches at CRP. GOES 16 PW imagery
shows that plume of higher moisture over CRP but lower values of
1.5 to 1.6 over SE Texas and over to LCH. Upper level analysis has
deep long wave trough over the western U.S. and an elongated
ridge through the plains into the Midwest. Weak cutoff low was
noted over the SE U.S. Water vapor imagery captures this pattern
well. With all this in mind, forecast will hold onto 20 PoPs for
Saturday but likely not see much coverage in shower activity.
Latest tends in the HRRR show some showers along the coast after
16Z and this activity moves inland. Coverage looks spotty at best.

Sunday through Tuesday moisture from the Gulf increases. Amplified
jet stream pattern continues through Tuesday even with one upper
low moving into the northern Plains and a jet streak diving south
across the Pacific NW Tuesday morning. A cold front looks to push
into the Texas panhandle but will be slow to move. Forecast will
keep mainly 30 PoPs with the increase in moisture and instability
but there will at least be some sinking motion from the ridge to
limit convection.

Higher rain chances look possible Wednesday into Thursday as the
cold front finally pushes southward. Upper low over the 4 Corners
region cuts off from the main flow and a trough over the Great
Lakes develops. This northerly flow aloft helps bring a re-
enforcing area of high pressure into the plains. Cold front should
push through the area on Thursday. The 850mb front lags behind
but pushes through on Friday. High pressure becomes more
entrenched over the Plains for next weekend. GFS still wants to
bring much higher moisture into the region ahead of the front but
the amount of QPF it generates Wednesday into Thursday does not
correspond well. Given the more consistent ECMWF in the extended
range, forecast tries to keep with lower PoPs the ECMWF suggests
with weak 500 mb ridging aloft and drier air pushing in with the
front.

Overpeck

MARINE...
A prolonged period of light to moderate onshore winds with seas
in the 2-3 foot ballpark continues, and is expected to continue
well into next week. Isolated to scattered showers and storms can
be expected daily. Tides also continue to run above astronomical
values with the continued onshore flow, and may run up to a foot
above normal to begin the new week. While this may start to
approach values at which we begin to see coastal impacts, current
expectations are that tides will stay below those critical values.
A cold front is expected sometime in the back half of next week,
which will increase winds and seas.


&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      91  72  90  71  90 /  20  10  10  10  30
Houston (IAH)              90  73  89  73  89 /  20  10  30  10  30
Galveston (GLS)            90  79  90  79  88 /  20  10  30  10  30

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...NONE.
&&

$$

Discussion...43



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