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Area forecast discussion
National Weather Service Houston/Galveston Texas
615 am CDT Wed Aug 21 2019

Aviation [12z taf issuance]...

Nighttime microphysics imagery not showing a lot in the way of
low clouds over the area this morning with a few showers
beginnning to develop just off the coast. The expectation will be
for a few showers and storms to form inland mainly affecting
klbx/ksgr and khou so will keep thunderstorms in the vicinity in tafs for those terminals.
Less certain there will be convection affecting kiah so decided to
go with a vcsh for now with kcxo/kuts/kcll staying dry. VFR
conditions are expected again overnight into Thursday am. There
looks like an increase in convection for Thursday as moisture
increases from the Gulf.

Overpeck

&&

Previous discussion /issued 350 am CDT Wed Aug 21 2019/...

Short term [today through Thursday morning]...
water vapor satellite imagery is picking up on a vorticity Max along
a shearing out trough over the Louisiana between 2 ridges. The
stronger ridge has become elongated over the Southern Plains so
there will be at least some easterly flow aloft over southeast Texas. There
is still some higher moisture with precipitable water values 1.8 to
2.0 inches over the area. This might be enough moisture to support
an isolated storm or two with day time heating. It will take some
convergence along the sea breeze and heating to get storms to
develop as the atmosphere is not quite as moist or unstable as
yesterday. Upper level ridge looks to be stronger as well with 595dm
to 593dm 500mb heights over the area.

Latest hrrr/href/WRF model runs seem on track with this kind of
evolution with showers and storms forming in the afternoon mainly
south of I-10 and east of I-69. Like the last couple of days the
main threats from any storms will be locally heavy rainfall causing
street flooding, lightning and gusty winds. Stronger storms could
produce a quick 1-2" of rain with 0.25" to 0.5" more common. With
there being less coverage in shower and thunderstorm activity
expected, high temperatures should be in the mid/upper 90s most
areas. Lone exception may be along the coast with low 90s but hedged
towards the mid 90s since storm coverage should be less and
therefore less cloud cover.

Overpeck



Long term [thursday morning through tuesday]...
the upper level ridge, centered northwest of southeast Texas begins to weaken and
retreat more to the west Thursday. As a result, more widespread
shower and thunderstorm activity is anticipated Thursday, with
precipitable water values (pws) remaining just shy of 2.0 inches
across much of the region, with the better moisture values
concentrated along the coast. The pressure gradient also begins to
tighten slightly in response the the upper level trough that
moves closer to the Upper Texas coast. Therefore, onshore flow will
continue to advect in better moisture values through the day
Thursday and into Friday.

Friday looks to be the best day for coverage of showers and
thunderstorms. The upper level trough should shift northward into
the northwest Gulf of Mexico before pivoting east on Saturday. As this
area of disturbed weather pushes north, very moist pws translate
with it, rising up to 2.2 to 2.4 inches by Friday afternoon.
Forecast soundings keep the atmosphere uncapped, with the
potential for some gusty winds beneath any stronger storms that
do develop. The best rainfall accumulation totals for the
Thursday through Saturday time frame still remains well to our
east over la and across the Gulf waters. At this time still
thinking a possible one to two inches will be possible over the
coastal counties and essentially along and south of I-10. That
said, the main change made to the forecast in this period was to
nudge pops inland down a bit, given the agreement amongst the
global models in terms of coverage. Otherwise, high temperatures
through the rest of the week will still reach into the low to
upper 90s, with cloud cover over the coast maybe keeping temps a
touch cooler.

The nam12 is drying things out a touch faster than the GFS on
Saturday, shifting the upper level trough east quicker than the
European model (ecmwf) and GFS in the latest model runs. Regardless, we should
still have enough moisture in place for the typical summertime
like showers and thunderstorms to develop, focusing along the
sea/Bay breezes. By Monday, the upper level ridge attempts to
build back in from the west, helping to suppress widespread
convection for the start of the work week.



Marine...
light to moderate onshore flow continues across the bays and Gulf
waters this morning and should prevail most of the day. Overall
expectation is for a typical Summer time pattern with onshore winds
increasing at night and decreasing during the day. Seas should
remain low through the next couple of days. We are going to have to
monitor a tropical disturbance now located over the northwest Caribbean Sea
that should move into the Gulf for the end of the week and weekend.
The system at this Point May cause a brief increase in winds and
seas Friday into Saturday but conditions may not even increase to
needing small craft exercise caution. We are not expecting any
tropical development.

Overpeck



&&

Preliminary point temps/pops...

College Station (cll) 99 76 98 76 97 / 10 10 10 0 30
Houston (iah) 96 79 94 78 93 / 30 20 30 10 50
Galveston (gls) 93 83 93 84 92 / 20 20 50 50 50

&&

Hgx watches/warnings/advisories...

Texas...none.
GM...none.

&&

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