Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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869
FXUS64 KHGX 211719
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1219 PM CDT THU JUL 21 2016

.AVIATION...
Very little to change in the forecast from the 12Z set. There has
been little enthusiasm for shower/storm development in short range
modeling, which seems reasonable given activity so far. Still,
given activity on water vapor imagery around the edge of the
ridge and plenty of moisture present, it seems prudent to leave
VCSH mentions nearer the coast. Overnight, guidance is hinting at
MVFR ceilings and visibility towards morning at several sites,
but for now will only introduce that where it occurred this
morning. Did toy with introducing VCSH or the like for the
extended portion of IAH, but would like to see how today pans out
to see just what mention might be needed - if any at all. 25

&&

.PREV DISCUSSION... /ISSUED 936 AM CDT THU JUL 21 2016/

UPDATE...
Previous forecast appears to be on track this morning, so no
major changes were made. We`re currently seeing some isolated
showers moving across the offshore waters this morning. Isolated
showers and thunderstorms are forecast to develop inland this
afternoon, primarily south of Highway 59. Another hot day is
in store for today, with high temperatures ranging from the low
90s near the coast to the mid/upper 90s inland. Portions of the
Brazos Valley and Piney Woods regions may approach or reach the
100 degree mark this afternoon. Although temperatures will be
quite hot, relative humidity in the 30%-40% range this afternoon
will keep heat index values around 100-107.  11

PREV DISCUSSION... /ISSUED 552 AM CDT THU JUL 21 2016/

AVIATION...
Some cirrus over the area this morning with some patchy fog near
KLBX. Expecting a cu field to develop between 15-17z with maybe a
few showers developing as temps warm into the mid 90s. Fcst
soundings show PW values AOA 2.00 inches this afternoon so can`t
rule out some scattered shra/tsra. HRRR/RAP continue to advertise
dry conditions across all TAF sites today. The gradient remains
weak and wind speeds should remain light and southeast today.
Generally VFR conds expected tonight with some patchy MVFR fog at
KLBX toward 12z. 43

PREV DISCUSSION... /ISSUED 353 AM CDT THU JUL 21 2016/

DISCUSSION...
Evening upper air analysis shows Southeast Texas remaining on the
southern periphery of a strong upper ridge centered over the
Southern Plains, with mid level heights nearly 600 decameters.
Precipitable water values across much of the region have fallen to
1.8 inches or less early this morning per SPC mesoanalysis, and
these lower moisture levels have resulted in a lack of convection
over the coastal waters. However, high resolution guidance
continues to advertise a few showers developing across the
offshore waters where greater moisture resides and have continued
low rain chances (20 PoPs) through the remainder of the morning.

For the rest of today, subsidence from the upper ridge will again
keep most of Southeast Texas dry. An isolated shower or
thunderstorm will again be possible along the sea breeze along the
coast (some may be capable of developing closer to the Interstate
10 corridor if an outflow boundary is produced from dying
convection), with greatest coverage southeast and east of the
Houston metro closer to better moisture over southwestern
Louisiana. If any convection does develop today, it will quickly
dissipate with sunset. Afternoon temperatures are expected to rise
into the mid to upper 90s inland, with low 90s along the coast. A
few sites across the Brazos Valley and Piney Woods regions
(including College Station) may even be able to reach 100. If
College Station reaches 100 today, it would be the first time it
has done so since August 15, 2015.

A warm start is expected again Friday morning with lows only
falling into the mid 70s to low 80s. The upper ridge appears to
nudge farther northwest of the region during the day on Friday and
there is fairly good model consensus for slightly higher PoPs on
Friday (as opposed to today) as a result. Have continued to
advertise 20-30 PoPs during the daytime hours with a somewhat more
active sea breeze. This shift may also allow for a few weak
disturbances rotating around the ridge to reach Southeast Texas on
Friday (further aiding in convective development). Interestingly,
tonight`s 00Z NAM continues the same trend it was showing 24 hours
ago, but with slightly slower timing (now in the late Friday-early
Saturday timeframe). Still have low confidence in this solution
given inconsistencies with other models and have kept the Friday
night forecast dry, but PoPs may need to be adjusted in this
timeframe for areas east of Interstate 45 should this feature
materialize.

A slow-moving shortwave trough remains off the Washington/Oregon
coasts early this morning per water vapor imagery and this
shortwave is forecast to slowly push east towards the Great Lakes
Friday through the weekend. As this happens, the upper ridge is
expected to flatten, expanding across the southern US and allowing
for a slight reduction in the influence of the ridge over
Southeast Texas as mid-level heights decrease. This will allow for
diurnally-driven scattered showers and thunderstorms to develop
this weekend and high temperatures a degree or two cooler (upper
80s coast to low-mid 90s inland) this weekend.

At the beginning of next week, the upper ridge begins to build
across the Great Basin as a secondary ridge develops over the
southeastern US. While medium range guidance disagrees on the
timing, persistent east/southeast mid-level flow will encourage
disturbances to retrograde under the upper ridge. While
temperatures are forecast to remain near seasonal normals, weak
lift associated with these disturbances will keep low daytime rain
chances in the forecast through the middle of next week.

Huffman

MARINE...
No significant changes to the forecast are expected through the
weekend for the marine areas as high pressure dominates the
weather pattern. High pressure over the eastern Gulf of Mexico and
low pressure over the central plains will produce generally light
to moderate E/SE winds across the area. A series of weak upper
level disturbances will bring scattered showers and thunderstorms
to the coastal waters Sunday through Wednesday. Tide levels will
remain slightly elevated through Friday. 43

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      99  77  98  77  97 /  10  10  10  10  20
Houston (IAH)              97  78  97  77  96 /  10  10  30  10  30
Galveston (GLS)            92  82  91  82  90 /  20  10  20  20  20

&&

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

$$



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