Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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404
FXUS64 KHGX 241511
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1011 AM CDT SUN JUL 24 2016

.UPDATE...
Marine convection has waned in the last hour or so as temperatures
rise and the land breeze shuts down. As opposed to yesterday,
which saw subsidence generally succeed in suppressing convection,
cumulus on the developing seabreeze front shows better vertical
development, and a couple showers have already popped up east of
Galveston Bay in Chambers County. Still, activity in our area
lags well behind what is being seen along the coast to the east.
This would indicate that we should see greater shower and
thunderstorm activity than yesterday, but it`s clear that we are
still seeing lingering influences of subsidence from the
retreating upper ridge. For that reason, did nudge up temperatures
slightly this afternoon, but the big picture forecast appears on
track.

One concern is that convection from the approaching vort max out
of Arkansas could push towards our area late this evening as
depicted in the NSSL WRF ensemble and the WRF-ARW. However, these
are still relative outliers and will hold off from raising evening
PoPs for now as the "slight chance" wording likely still covers
the potential. Will keep an eye on convective trends in Southern
Arkansas and Louisiana though.
25

&&


.PREV DISCUSSION... /ISSUED 632 AM CDT SUN JUL 24 2016/

AVIATION...
The HRRR and RAP13 both agree with bringing a few more showers
into the coastal areas this morning as compared to 24 hours ago.
The HRRR was a bit overdone as compared to the 1130Z radar but was
on the right track over the Gulf. The upper high will still have
some influence; however, slightly better rain chances are expected
this afternoon as the seabreeze combines with the upper pattern.
For the big metro airports, best chances for thunderstorms will be
from 19Z to 00Z this afternoon. Less chances are expected to the
north of KIAH and KCXO.

For Monday, better chances for thunderstorms are still looking to
occur mainly in the afternoon. However, there is some indication
that isolated coverage may begin during the mid and late morning
period.

40

PREV DISCUSSION... /ISSUED 447 AM CDT SUN JUL 24 2016/

DISCUSSION...
At 3 AM, a weak trough of low pressure extended from western KS
to southern NM. A weak 850 mb high was centered over SE OK with a
plume of deeper 850 moisture extending from southern AR to E TX
and LA. At 300 mb, an expansive ridge of high pressure was
centered over NE NM but its reach remains very broad extending
from S CA to the FL panhandle. The LCH 00z sounding showed PW
values at 2.10 inches and very little capping. Water vapor imagery
shows several weak disturbances heading west with one disturbance
approaching the northern half of SE TX this morning and a second
disturbance over SE LA approaching in the afternoon. Fcst
soundings show PW values ranging from 1.85 to 2.15 inches.
Soundings also show a weak but breakable cap in the 800-700 mb
layer. The RAP/ECMWF are the most aggressive today with afternoon
convection and the HRRR has begun to trend toward this solution as
well. That said, have trended PoPs lower for today since the ridge
is in nearly the same position it was 24 hours ago, feel
subsidence may be a bit stronger as advertised by the GFS. 30 PoPs
will cover things today and this may be a bit generous.

After the evening convection wanes, expect skies to clear with
clouds moving back in after 09z. An inverted 500 mb trough will
be approaching from the east but the mid level flow between the
ridge out west and the trough over the Gulf will bring a strong
disturbance into the area from the northeast. This feature will
trigger shra/tsra over the NE zones early in the morning with
convection increasing in coverage as the system moves SW. Will
maintain likely PoPS for Monday. Some of the rain on Monday could
be locally heavy as storm motions are around 5-6 kts. Fcst
soundings show PW values between 2.20 and 2.40 inches but the NAM
and GFS differ with the moisture profile as the GFS shows some dry
air near 700 mb while the NAM has a nearly saturated layer between
900-500 mb. Will keep rain chances going Monday night as the
inverted trough over the Gulf pushes west.

SE TX will lie on the east of the inverted trough axis on Tuesday.
PW values will be between 2.20 and 2.40 inches in the morning with
some drying noted in the afternoon. Fcst soundings are in better
agreement with a saturated layer between 925-625 mb so feel
best rain chances may actually be on Tuesday. Will carry likely
PoPS areawide. Again storm motions look slow, so locally heavy
rain a possibility.

GFS and ECMWF differ with regard to mid-late week rain chances as
the GFS dries things out while the ECMWF keeps things wetter. The
inverted trough exits the area and a ridge over FL tries to build
across the Gulf into TX but the periphery of the ridge looks to
stop over LA. This will keep SE TX in a weakness aloft. A weak
s/wv trough will also be moving across the central plains mid-week
which should reinforce the weakness/lower heights over the area.
Will raise PoPS on Wednesday to high end chance as both the ECMWF
and Canadian look wet and lower PoPS to 30 on Thursday as slightly
drier air moves into the area from the east. Upper level ridging
tries to assert itself next week from the east and am expecting
rain chances to decrease at that time with temperatures going back
up. 43

MARINE...
Onshore winds are expected through the week. A more moist and
unstable airmass is expected to move over the marine areas and bring
increasing coverage of showers and thunderstorms on Monday and
Tuesday. There is some indication that the coverage could linger
through Wednesday.

40

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      98  78  95  76  92 /  20  20  50  30  60
Houston (IAH)              96  79  94  78  92 /  30  20  60  30  60
Galveston (GLS)            92  82  90  82  88 /  30  30  60  40  60

&&

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

$$



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