Area Forecast Discussion
Issued by NWS Austin/San Antonio, TX

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000
FXUS64 KEWX 240547
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1247 AM CDT Sat Jun 24 2017

.AVIATION...
Showers and thunderstorms from Brackettville to Del Rio to the Big
Bend will sag to the southwest. Have prevailing for KDRT 06Z-0730Z.
Showers and thunderstorms from KBBD to K6R6 will sag southwest, as
well. However, will carry only VCSH for KDRT as those showers and
thunderstorms will slowly decrease. Other showers and thunderstorms
from the KDFW area eastward will move to the southwest overnight,
possibly reaching our area early Saturday morning. Have introduced
VCSH mention to KAUS, KSAT, and KSSF after 16Z. For the remainder of
forecast, outflow boundaries and a cold front will generate
additional showers and thunderstorms. For now, will only go with
VCSH. VFR skies will prevail early, then stratus with IFR/MVFR CIGs
will develop much of our area overnight into morning hours. However,
outflows will disrupt the stratus development with timing uncertain.
CIGs mix to VFR by midday on Saturday. Brief IFR/MVFR CIGs/VSBYs are
possible in showers and thunderstorms. South to southeast winds 5 to
12 KTs will prevail, except east to northeast behind the front and
variable mainly northerly 15 to 30 KTs with gusts to 45 KTs in and
near the stronger thunderstorms.

&&

.PREV DISCUSSION... /ISSUED 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 CWA 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.

PREV 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
MCS 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.

PREV 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              73  88  71  90  71 /  30  50  30  40  20
Austin Bergstrom Intl Airport  72  87  70  89  69 /  30  50  30  50  20
New Braunfels Muni Airport     72  89  70  90  70 /  30  50  30  50  20
Burnet Muni Airport            70  85  69  88  69 /  30  40  30  40  20
Del Rio Intl Airport           76  94  74  94  74 /  20  30  20  30  20
Georgetown Muni Airport        70  86  69  89  69 /  30  40  30  40  20
Hondo Muni Airport             73  92  71  92  71 /  20  50  20  50  20
San Marcos Muni Airport        72  89  71  89  70 /  30  50  30  50  20
La Grange - Fayette Regional   74  88  72  89  72 /  40  50  30  50  20
San Antonio Intl Airport       74  91  73  91  72 /  20  50  30  50  20
Stinson Muni Airport           75  91  73  91  73 /  20  50  30  50  20

&&

.EWX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

Mesoscale/Aviation...04
Synoptic/Grids...05
Public Service/Data Collection...Williams



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