Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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427
FXUS64 KHGX 260450
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1150 PM CDT Tue Jul 25 2017

.AVIATION...
Showers continued to approach the coastal sites at 0430Z and
expect these to continue at least through 10Z; although, the
trends for the rainfall area size was diminishing. An outflow will
move inland and could help to generate isolated showers further
inland than KGLS and KLBX. There have been indications that wind
gusts to 25 to 30 knots are possible with the strongest showers
associated with the outflow boundary. Will need to focus on the
movement of the storms off of the coast to see how far inland they
will get during the overnight hours.

After 09-10Z, there is a chance that MVFR ceilings could develop.
Best chances look to have VFR conditions with a scattered MVFR
deck per the latest model forecasts. On Wednesday a moisture
channel from off of the Gulf of Mexico will continue over or near
the I-45 corridor. Chances for showers and thunderstorms will be
best near the coast by 16Z and then inland after 18Z.

40

&&

.PREV DISCUSSION... /ISSUED 901 PM CDT Tue Jul 25 2017/

DISCUSSION...
High pressure over southern LA and a trough of low pressure over
eastern CO will maintain light onshore winds tonight. Winds may
not fully decouple over the western half of the V+CWA where the
gradient looks tighter. SHRA/TSRA continue to develop in a
corridor of deeper moisture that extends from about Hempstead to
Freeport and then offshore. An 850 mb High was located over the
north central Gulf and deeper moisture was rotating into SE TX on
the back side of this feature. At 300 mb, there was a well defined
albeit weak trough axis that extends into SE TX. The combination
of the upper level feature and deeper moisture should allow for
additional showers overnight, mainly over the marine zones and
adjacent coast. Have increased PoPs slightly for tonight and
bumped up mins a bit due to mixing out west and more cloud cover
toward the coast.

Also bumped PoPs up to 30 percent for areas south of Houston on
Wednesday and feel this still might be too low. An upper level
disturbance will move across SE TX on Wednesday and coupled with
an increase in moisture (PW values reach 2.15 inches) and a subtle
weakness aloft will trigger SHRA/TSRA on Wednesday afternoon.
Numerical guidance not too impressive but other parameters suggest
higher rain chances. 43

PREV DISCUSSION... /ISSUED 648 PM CDT Tue Jul 25 2017/

AVIATION...
Moisture channel over SE Texas can be seen by satellite derived
PWs of 2 inches nudging inland between KGLS and KLBX and by the
isolated to scattered showers and thunderstorms inland to west of
KCXO. Expect these to diminish by 01Z to 02Z with the lost of
solar heating; however, with the higher moisture available
isolated showers could linger into the mid evening. Not as
confident that the showers will make it as far east as KIAH and
KCXO or as far inland as KCLL and KUTS.

Model data and statistical output suggests at least a scattered
MVFR deck after 09Z. Confidence in any more coverage than that was
low. There is a slight chance for MVFR due to restricted
visibility or to ceilings -- confidence is low but best
possibility looks to be KCLL and possibly KLBX and KSGR. For
Wednesday VFR conditions with at least a slight chance of showers
and thunderstorms after 17Z.

40

PREV DISCUSSION... /ISSUED 355 PM CDT Tue Jul 25 2017/

DISCUSSION...
KHGX radar has been fairly quiet today...except for a stray SHRA
near Eagle Lake earlier this afternoon. All in all, it does look
like the combination of slightly lower PWs/weak upper level ridging
is currently helping to keep things quiet across SE TX. But we
are starting to see some changes offshore. Strengthening flow from
the Gulf will be drawing slightly deeper moisture (PWs near 2.2")
into the area tonight through tomorrow. Combined with daytime
heating and perhaps the seabreeze, isolated to widely scattered
activity will be possible. As this surge of moisture mixes out and
high pressure builds back into the area, rain chances to lower a
bit as temps/heat indicies climb a bit for Thurs/Friday. Heat
index values are progged range from 105 to 110F during this time
frame...but we will have to keep an eye on things Saturday.

Models remain very consistent with bringing a cold front through
the region from the NE on Sat. While there is still a certain amount
of skepticism with this scenario...it is getting harder to ignore
the long range guidance. That being said, the big concern with
this boundary looks to be the progged PWs of 2.2-2.6" along and
ahead of the front and where it could potentially stall. For now
will keep with CHC POPS for this time frame. Also of note is the
possibility of very warm temps Sat afternoon given the insolation
ahead of this boundary. 41

MARINE...
Wind speeds will approach SCEC conditions this evening, but should
remain right below criteria. With high pressure in control, a
typical summer like pattern can be expected, with occasionally
scattered showers in the afternoon hours during peak day time
heating. Light to moderate south to southeast winds with wave
heights between 2 to 3 feet can be expected through Wednesday,
eventually dropping to 2 feet through Saturday. A weak boundary
will push into the bays and nearshore waters early Sunday morning
with northerly winds filling in behind this passage.

Hathaway

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      77  99  77 100  78 /  10  20  10  10  10
Houston (IAH)              78  95  77  97  78 /  10  20  10  10  10
Galveston (GLS)            82  89  82  93  82 /  30  20  10  20  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...High Rip Current Risk from 8 AM CDT Wednesday through Wednesday
     evening for the following zones: Brazoria...Chambers...
     Galveston.

GM...NONE.
&&

$$

Discussion...43
Aviation/Marine...40



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