Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 150309
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1009 PM CDT Mon Aug 14 2017

.UPDATE...
Radar imagery show showers have dissipated across Montgomery and
Harris counties this evening, leaving clear skies across much of
SE TX. Low temperatures tonight will remain above normal for this
time of year, with low 80s along the coast and upper 70s further
inland.

Minor changes were made to the forecast this evening.
Expecting a small break Tuesday from the dominant 500 mb ridge
which weakened and shifted west this afternoon, leaving us in an
area of weakness throughout the day tomorrow. Went ahead and
raised PoPs slightly to account for the better coverage indicated
by the 00Z HRRR and RAP13 short term guidance. With the seabreeze,
bay breeze, and potential pocket of positive vorticity (as
indicated by the 18Z GFS) moving across the region acting as
possible forcing mechanisms for tomorrow`s activity, scattered
shower and thunderstorm development will be possible mainly along
the coast and southeastern counties of the CWA. Tomorrow still
looks to provide the best chance of precip through the rest of the
week.

Although tomorrow will once again be another warm day,
areas that see the convection tomorrow could result in their high
temperatures being a degree or two cooler than what we`ve seen
over these last few days. Therefore, forecast high temperatures
along the coast and eastern counties are in the upper 80s to mid
90s. Regions that do not see precip tomorrow will still be
battling the heat with high temperatures reaching up into the mid
to upper 90s once again. By Tuesday 00Z, upper level ridging
begins to build back in from the east and should shift overhead,
parking itself over SE TX through the remainder of the week.

Hathaway


&&

.PREV DISCUSSION... /ISSUED 657 PM CDT Mon Aug 14 2017/

AVIATION...
Other than some (vicinity) thunder in and around CXO this
evening...VFR will prevail through the sunrise hour. Periodic
short-lived MVFR ceilings over far interior hubs...scattering out
to a FEW-SCT cumulus field tomorrow afternoon. An analogous
scenario with light onshore winds and isolated late day shower
activity. 31

PREV DISCUSSION... /ISSUED 313 PM CDT Mon Aug 14 2017/

DISCUSSION...
The main driver of the forecast over the next several days appears
to be the strength and location of ridging aloft, which will nudge
temperatures modestly up or down, and determining whether there will
be potential for scattered showers and storms, or a more suppressed
atmosphere. Day to day changes will likely be rather small into the
weekend, with only subtle changes. Thus, the focus will almost
certainly continue to be the characteristic hot, humid summer of
Southeast Texas.

Luchs

NEAR TERM [Through Tonight]...

Through 2 pm, the radar has been pretty quiet, outside of a couple
isolated showers in Liberty County. Though some subtle features
could be seen in the low level GOES-16 water vapor imagery,
subsidence under the ridge appears to largely be winning out,
except in the vicinity of Galveston Bay (which likely explains the
isolated showers in Liberty County). Meanwhile, after a fast
start, temperature rises this afternoon have leveled out somewhat.
The idea of a hot, humid day that sees the heat index near the
coast top out just below heat advisory thresholds still seems
safe.

This evening, any showers that do manage to initiate today should
wind down very quickly. However, despite the loss of solar heating,
temperatures aren`t likely to go into a tailspin. With overnight
dewpoints in the middle 70s to around 80, low temperatures tonight
will again be very warm. Houston, Hobby Airport, and Galveston are
all currently at least tied for their record warm mins today, and
though it may be close, there`s a strong chance all of them hold on.

SHORT TERM [Tuesday Through Wednesday Night]...

The upper ridge looks to briefly weaken Tuesday, and both the GFS
and Euro suggest some subtle midlevel vorticity slides across
Southeast Texas. But don`t want to sell out too hard on PoPs, as the
NAM modestly lowers heights, but doesn`t show any vort lobes and as
a consequence looks pretty dry. Put the highest PoPs in that subtle
Galveston/Gulf seabreeze convergence zone, which may benefit most
from the lower heights aloft. Temperatures may be a touch (read: a
degree or two) cooler, but with such a brief, modest change in the
column and such a warm start to the day, there should be little to
no change in temps.

After that, look for things to settle back down Wednesday as ridging
attempts to build in yet again from the east. Again, we`re only
looking for modest changes in heights and surface pattern, so
changes will be minimal, but may ultimately lock in Tuesday as the
best potential for rain, as Wednesday backs down to isolated or
widely scattered development.

Both days again look to have heat index values that are on the
fringe of the heat advisory threshold again. Whether an advisory
is necessary will likely depend on sky cover and the state of
boundary layer moisture, determining if dewpoints will mix out or
stay high enough to boost the heat index past 108. Both aspects
are very difficult to forecast from much range, so it seems calls
on any advisories will be a day to day call. Expect this trend to
continue through the week.

LONG TERM [Thursday Through Monday]...Discussion

Pretty good agreement in the guidance for a 595-ish midlevel high
stacked over a surface high to develop over the northern Gulf
coast and drift westward late in the week. This seems likely to
clamp down on rainfall potential pretty well for the late week,
with only modestly better potential this weekend on the backside
of the high. Another thing to watch for this weekend that`s
emerged in the 12Z guidance is a TUTT moving across the Gulf
behind this ridge. This may help to boost rainfall potential by
lowering heights and increasing vorticity advection over the
region. However, this is a relative newcomer with this morning`s
model runs and we`re looking nearly a week out, so it`s probably
best not to commit too much to a specific scenario.

Though a ridge in the area of 595 dm isn`t astoundingly strong by
the area`s standards, we should see response in temperatures from
subsident warming over time as it moves slowly along. It may not be
quite as apparent near the coast with the moderating water, but do
introduce isolated triple digit temps in the northwest towards
College Station late in the work week.

MARINE...

Moderate onshore winds (mainly from the south) will persist for the
next several days with caution level speeds expected during the
overnight hours. Winds will gradually weaken toward the end of the
week and over the weekend.  42

CLIMATE...

Houston Hobby is on track to break a record high min temp today.
Low so far is 81, record is 80 (2015). Both Galveston and City of
Houston (IAH) are on track to tie their previous records.
Galveston with 84 in 2010 and Houston with 81 in 1951.

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      77  98  78  98  78 /  10  10   0  20  10
Houston (IAH)              79  95  81  94  81 /  10  40  10  20  10
Galveston (GLS)            84  90  85  89  85 /  10  30  20  20  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 9 AM CDT Tuesday for
     the following zones: Coastal waters from Freeport to the
     Matagorda Ship Channel out 20 NM...Coastal waters from High
     Island to Freeport out 20 NM...Galveston Bay...Matagorda
     Bay...Waters from Freeport to the Matagorda Ship Channel
     from 20 to 60 NM...Waters from High Island to Freeport from
     20 to 60 NM.

&&

$$

Update...08



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