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Area forecast discussion
National Weather Service Austin/San Antonio Texas
841 PM CDT Fri Jun 23 2017

Update...
heat indices have fallen below heat advisory criteria into the lower
100s and 90s across the region, so we have allowed the advisory to
expire. Attention now turns towards the north and west in particular
where a relatively strong cold front reinforced by convection will
help provide south central Texas with some relief form the heat
tomorrow. A strong to severe line of showers and thunderstorms is
continuing to push south through San Angelo towards northern Edwards
and Val Verde counties where cape values are still in excess of 2000
j/kg, but cinh values should continue to increase given the loss of
daytime heating. Hi-res models are generally not handling the current
intensity and speed of convection over san angelo's County Warning Area well. Given
the frontal forcing and relatively fast speed of the system, we have
increased pops to 30 percent along our their southern border before
tapering them back quickly to the south as these cells would reach
Edwards and Val Verde counties by 10 PM, but should weaken before
making it too much farther south.

The rest of south central Texas should remain dry for the majority of
the evening and overnight hours. There is still some uncertainty
about whether or not showers and thunderstorms along the cold front
over The Ark-la-tex region and North Texas will be able to expand
upscale as they move south or southwest towards sunrise. Right now,
the outflows themselves are probably not strong enough to push the
front into Burnet, Williamson, and Lee counties before sunrise.
However, forcing associated with a weak low-level jet and shortwave
to our north may be enough to allow for storms to move into the
region in northerly flow aloft prior to sunrise. Thus, we have
retained slight pops late in the overnight hours to account for this
uncertainty even though the rain chances will most likely hold off
until after sunrise. The best rain chances for tomorrow currently
appear to be during the morning hours with a dissipating line of
showers of thunderstorms along the front and tomorrow afternoon into
the early evening hours as scattered showers and thunderstorms
redevelop along the front and/or remnant outflow boundaries. Rain
chances may be a bit higher in the coastal plains where sea breeze
forcing may play a role, with the highest rain amounts where the sea
breeze collides with the front. However, we left tomorrow's forecast
unchanged for now and will let the midnight shift reevaluate.

&&

Previous discussion... /issued 655 PM CDT Fri Jun 23 2017/

Update...
see below for the 00z aviation discussion...

Aviation...

Currently VFR at all taf sites with southeasterly winds. VFR is
expected to continue until around or shortly after midnight tonight,
at which time cigs are anticipated to lower to MVFR at the Interstate
35 sites. The primary forecast question is how far south will the
cold front reach, as well as the coverage and intensity of any
showers or thunderstorms associated with it. Presently the cold front
is analyzed from near Hobbs nm northeast through southeastern OK and
slowly making its progression southward. A complex of showers and
storms are ongoing from roughly Midland eastward toward the Abilene
area. High-res models suggest this activity should dissipate before
entering into our northwestern counties. However, models show a new
mesoscale convective system forming in the dfw region Saturday morning and heading southward.
It is unclear if this will stay together long enough to reach aus,
but have included vcsh in the aus taf starting at 15z. Additional
showers and thunderstorms are possible Saturday afternoon and evening
for the Interstate 35 sites.

Previous discussion... /issued 317 PM CDT Fri Jun 23 2017/

Short term (tonight through Saturday night)...
hot and humid conditions continue across south central Texas this
afternoon. Given recent observations and short term model guidance,
the current heat advisory is in good shape and will continue until 8
PM. Southeast winds remain intact this evening and cooling after
sunset will be rather slow given plenty of low-level moisture in
place. Rain chances for tonight will remain low and generally
confined to areas north of a del Rio to Austin to La Grange line. The
hi-res models continue to show convection developing across west
central Texas this evening, with some of this activity possibly
reaching the southern Edwards Plateau and western Hill Country around
or shortly after midnight. This convection is expected to weaken as
it moves southward into our region. Elsewhere, the hi-res models also
show convection developing across North Texas early Saturday morning
as a cold front moves southward. We should see enough convection to
help usher the cold front southward during the morning hours on
Saturday. The front will likely halt it's southward progress during
the afternoon and should remain north of the Highway 90 corridor.
However, we should see enough convergence along the front and outflow
boundaries to initiate scattered shower and thunderstorm development
on Saturday. Temperatures will cool given the expected increase in
cloud cover and precipitation. However, areas south of the front
could still see highs in the mid 90s to near 100.

Long term (sunday through friday)...
a reinforcing shot of high pressure moving into Oklahoma and
Arkansas early Sunday morning should be enough to help the front
slide a little farther southward on Sunday. We should continue to see
a chance for scattered showers and thunderstorms, with better coverage
in the afternoon and evening during peak heating. As we head into
early next week, the frontal boundary will continue to weaken and
become ill-defined. A fairly active northwest flow aloft is still
expected to continue into early next week and we'll continue a
chance for showers and storms across south central Texas. We should
see enough influence from a subtropical ridge building in from the
west toward the middle of the upcoming week for a return of warm
temperatures and dry weather for most areas. We can't rule out some
sea breeze convection near the coastal plains and Highway 77 corridor
and will mention a low chance in the forecast.

&&

Preliminary point temps/pops...
Austin Camp Mabry 78 91 73 88 71 / 20 40 30 50 30
Austin Bergstrom Intl Airport 77 91 72 87 70 / 20 40 30 50 30
New Braunfels Muni Airport 77 92 72 89 70 / 10 40 30 50 30
Burnet Muni Airport 76 87 70 85 69 / 30 40 30 40 30
del Rio Intl Airport 80 96 76 94 74 / 20 20 20 30 20
Georgetown Muni Airport 77 89 70 86 69 / 30 50 30 40 30
Hondo Muni Airport 78 95 73 92 71 / - 30 20 50 20
San Marcos Muni Airport 78 92 72 89 71 / 10 40 30 50 30
La Grange - Fayette regional 78 92 74 88 72 / 20 40 40 50 30
San Antonio Intl Airport 79 93 74 91 73 / - 40 20 50 30
Stinson Muni Airport 79 94 75 91 73 / - 30 20 50 30

&&

Ewx watches/warnings/advisories...
none.
&&

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