Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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538
FXUS64 KHGX 190450
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1150 PM CDT Tue Jul 18 2017

.AVIATION...
VFR conditions are expected to prevail through the taf period. A
few spots of very patchy fog may develop right around sunrise this
morning across areas that received rain today, but confidence is
too low to include in any tafs at this time. Showers and storms
will likely develop across the southern half of the area (KIAH and
southward) tomorrow, with less coverage expected than on Tuesday.
11

&&

.PREV DISCUSSION... /ISSUED 959 PM CDT Tue Jul 18 2017/

UPDATE...
Radar cleared out around 8 PM and am expecting a stable interior
air mass to keep any overnight shower/storm re-development focused
over the Gulf waters. As has been the case these past couple of
days...scattered early morning Gulf -TSRA activity may clip the
coastal counties through sunrise then creep further inland through
the early afternoon hours. Further northern activity may blossom
later in the day once the lower 90s are met...but the bulk of the
precipitation should remain over the southern third of the CWA.
Energy is forecast to move down an East Coast trough axis and pinch
off around the south and eastern periphery of the large Central U.S.
ridge. This scenario should contribute to maintaining a region of
disturbed weather paralleling the Gulf Coast. An easterly flow
pattern should allow this unsettledness to still be a player for yet
another day...equating to scattered showers and embedded ordinary
thunderstorms. The main threats will be early day waterspouts that
could travel ashore as weak tornadoes...latter day bursts of
lightning and very localized flooding issues from 1 to 2 inch per
hour rainfall rates. The combination of low to mid 90 ambient
afternoon temperatures and lower to middle 70 dew points should
translate to Wednesday afternoon 100 to 105 F maximum heat indices.
31

PREV DISCUSSION... /ISSUED 315 PM CDT Tue Jul 18 2017/

DISCUSSION...
The convection which occurred over areas along and south of the
I-10 corridor earlier today has diminished. Scattered showers and
thunderstorms were occurring along the northward and westward
moving outflow boundaries at 3:00 PM. Tweaked the rain chances
for the southwestern and northern counties for the rest of this
afternoon to account for these ongoing storms. Could see an
isolated shower or thunderstorm to redevelop to the south and
southeast but with the cirrus shield overhead think these will be
limited.

The deep layer weak trough overhead of SE Texas will likely linger
overhead one more day before the deep layer upper level ridge in
the Plains edges southward. This pattern should lead to slightly
warmer temperatures and less rain chances. On both Wednesday and
thursday the maximum heat indices could reach into the 105 to 107
for a lot of locations with some isolated locations reaching 108.
Do think that the best chances for rain will be on Wednesday;
however, enough moisture will linger overhead to keep daily shower
and thunderstorm chances in place for Thursday and Friday. By
Saturday the general upper level troughiness over the Atlantic
Region will again extend into the Upper Texas coastal areas. Both
the GFS and ECMWF show a 500 mb low pressure area over the Mid
Atlantic moving southwestward into at least the lower Mississippi
Valley during the weekend. Both models differ on the evolution of
this system early next week but both show the weak trough again
developing either overhead SE Texas or near the Upper Texas coast.
For this reason, kept daily chances for showers and thunderstorms
in place for most areas through Tuesday. 40

MARINE...
A light onshore flow is expected through the end of the week with high
pressure over the eastern Gulf and lower pressures over West Texas.
Night time winds will be slightly stronger especially toward the end of the
week as low pressure moves across the southern plains. Tide levels will
remain slightly elevated through the week but will remain below critical
thresholds. 43

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      75  96  76  97  77 /  20  10  10  20  10
Houston (IAH)              74  94  76  95  77 /  20  30  10  30  10
Galveston (GLS)            81  89  81  90  82 /  20  30  10  30  20

&&

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

$$

Discussion...31
Aviation/Marine...11



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