Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 240453
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1153 PM CDT Fri Jun 23 2017

.AVIATION.../06Z TAF/
Squall line over NE Texas should continue to build south with a
strong outflow boundary surging ahead of it. Thunderstorm activity
should be decreasing with outflow surging out ahead of it. Latest
HRRR trends are not handling situation well, but WRF-ARW seems to
be continuing its trends from its 12z yesterday to 00z today
model runs. The 12Z Texas Tech WRF was on track but the 18z runs
seems to have convection too far east. New 00Z run seems too slow
with the line and none of the models have severe/strong convection
over SE Texas that is occurring. That said, modified TAFs at
KCLL/KUTS/KCXO to account for outflow and possible storms timed
around 11-12Z. Outflow may become a focus for convection later in
the day so will keep the same timing for afternoon thunderstorm
activity.

Overpeck

&&

.PREV DISCUSSION... /ISSUED 920 PM CDT Fri Jun 23 2017/

DISCUSSION...
A cold front was located from near Texarkana to just south of
Hobbes,NM at 7:00 PM. Storms were developing along and ahead of
the front over southern AR. Water vapor showed an upper low over
the southern Gulf of Mexico. An elongated moisture axis was
present west and northwest of this low over the central Gulf while
a dry area was further west over the Upper and Middle Texas
coastal waters.

The 00Z NAM12 was pushing the storms over AK southward toward SE
Texas overnight tonight. However, the model showed a weakening
trend in the storms with very little coverage by the time the
storms reached into the northern portions of the forecast area.
Better chances will occur after mid morning as the front moves in
from the north and the deeper layer moisture over the Gulf arrives
from the southeast. The latest models pretty much agree with the
current forecast. Did tweaked the rain chances mainly to take out
the isolated rain chances over the north and add isolated rain
chances over the offshore coastal waters for the rest of this
evening.

40

PREV DISCUSSION... /ISSUED 629 PM CDT Fri Jun 23 2017/

AVIATION.../00Z TAF/
Surface analysis has cold front boundary from Arkansas along the
Red River to west Texas. This has allowed for a line of storms to
form in Arkansas. Warm sector airmass over much of Texas south of
the boundary remains relatively capped except for west Texas.

Tonight we need to monitor the evolution of the convection
organizing in Arkansas. The 12Z WRF-ARW and TX Tech WRF-ARW both
show this line of storms pushing south and even southwest towards
KCLL to KUTS by 06-09Z Saturday. The KCLL/KUTS/KCXO TAFs may need
to be adjusted for this evolution but will wait and see for now.
Outflow may play a role in tomorrow`s convection for the area but
for now these models do not show much redevelopment of storms
until the afternoon like most other models. The TX Tech WRF does
start storms around 16-17Z along the coast so may need to adjust
the VCTS used in the TAFS for 18Z. HRRR is less robust with the
outflow and any storms redeveloping but still need to watch its
trends.

Otherwise TAFs will be close to the previous 18Z update with MVFR
ceilings overnight and mention of showers starting in the morning
hours turning to VCTS.

Overpeck

PREV DISCUSSION... /ISSUED 342 PM CDT Fri Jun 23 2017/

DISCUSSION...
A hot afternoon is well underway for Southeast Texas with 3 PM CDT
temperatures in the low to mid 90s inland and heat index values
ranging from 98 to 107. Visible satellite imagery shows a
scattered to broken stratocumulus deck developing around 4500 feet
and spreading south within an area of isentropic lift on the 310 K
surface. RAP guidance shows this area of lift gradually
translating east over the next few hours (likely as the remnants
of Cindy pull farther away from the region), allowing at least
some of these clouds to translate towards the south and east with
it. For those areas lucky to get some shade from these clouds,
temperatures may quickly drop 2-3 degrees and provide some relief
from the heat. Otherwise, cannot rule out a stray shower along the
coast or across the far extreme eastern counties through the
remainder of the day but this would be the exception and not the
rule.

Not much cooling is expected overnight with lows only falling into
the mid 70s to low 80s, but rain chances will increase across the
region on Saturday and Sunday as Southeast Texas remains situated
in a relative upper level weakness between two ridges. Speed
convergence along the coast Saturday will result in scattered
morning showers, with the northern counties seeing a thunderstorm
complex along an approaching (weak) cold front also during the
morning hours. Regional radar mosaic already shows storms
beginning to develop along this cold front across portions of the
Low Rolling Plains and along the Red River, with additional
upscale growth into a thunderstorm complex expected through the
remainder of the afternoon and evening hours as the front pushes
south towards the region.

The cold front looks to make a run for the Interstate 10 corridor
through the remainder of the morning hours Saturday, stalling
near or north of it as a sea breeze pushes inland during the late
morning and afternoon hours. Daytime heating and the collision of
both of these boundaries is expected to result in the development
of scattered to numerous showers and thunderstorms on Saturday,
with greatest coverage centering wherever the boundaries collide
(likely near Interstate 10). Convection should wane with loss of
heating by Saturday evening. Another round of morning showers are
expected on Sunday, with scattered to numerous thunderstorms again
developing with daytime heating and likely focusing along
wherever the remnant frontal boundary (or outflow boundaries from
Saturday`s convection) is. The front won`t have much of an effect
on temperatures but increased clouds on Saturday and Sunday will
keep temperatures a few degrees cooler than today with highs in
the mid 80s to low 90s.

Similar to what the previous forecast noted, storm motions will
be very slow both days (around 5 knots Saturday, 10 knots Sunday)
and this, combined with precipitable water values 1.8-2 inches,
will result in the threat for locally heavy rainfall and the
potential for some localized flood issues as thunderstorms have
the potential to remain nearly stationary before collapsing. SREF
plumes show forecast rain totals generally in the 1-2 inch range
during this time, but would not be surprised to see some isolated
2-3 inch totals occur given the aforementioned environmental
conditions. Will also have to keep an eye on a gusty wind threat
as well on Saturday. Relative humidity progs show drier air
evident over the northwest Gulf on afternoon water vapor imagery
working its way into the region from the south/southwest. This
drier air would help enhance evaporational cooling, accelerating
downdrafts and creating the potential for gusty winds in stronger
convection on Saturday.

The region remains under this relative weakness in the upper flow
through the middle of the upcoming week, with mainly daytime
shower and thunderstorm chances inland through mid-week.
Expect these chances to gradually decrease early to mid next week
as 500 MB heights increase and atmospheric moisture content drops
a bit. These increasing mid-level heights and decreasing rain
chances will also result in gradually warming temperatures with
highs increasing to near or slightly above normal (low to mid 90s)
by the end of the next work week.

Huffman

MARINE...
Winds are slowly diminishing today, and seas should also come
down with them on a bit of a delay. Though winds may not quite be
at the SCEC threshold, the lag in waves should justify keeping it
in place into tonight. Going into the weekend and early next week,
light to moderate flow is expected, generally onshore. An
approaching front may back winds slightly to more easterly from
Sunday, but will still be generally onshore. Some stronger winds
may be possible mid to late week.

Tides also remain elevated, and astronomical high tide at around
two feet at Galveston are not aiding matters. Another chance at
coastal flooding in vulnerable areas around high tide early
tomorrow morning can`t be ruled out. Will hold off on another
Coastal Flood Advisory for now to gauge tidal behavior through low
tide and into the upswing towards high tide.

Luchs

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      77  90  73  87  71 /  20  40  50  60  30
Houston (IAH)              78  90  75  87  73 /  20  70  40  70  40
Galveston (GLS)            81  88  80  87  78 /  30  40  20  50  50

&&

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

$$

Discussion...40
Aviation/Marine...39



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