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

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FXUS64 KEWX 240540 AAC

Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
1240 AM CDT Sat Aug 24 2019

Convection continues this evening west of I-35 and currently no
impacts at the terminals. Convection will be the main concern for
this forecast period. MVFR cigs are developing at the I-35 sites and
the MVFR conditions will prevail through 13Z-15Z. Do expect DRT to
remain VFR. Light S/SE winds are expected through sunrise when winds
become E/SE 9-13 knots after 15Z. Winds will be stronger and gusty
in or near any convection. Looks like best potential for SHRA/TSRA
will be after 20Z at the terminals so have included VCSH during the
period from 20Z to 03Z at all locations. Once convection develops
forecast will updated for timing and wind potential.


.PREV DISCUSSION... /ISSUED 1013 PM CDT Fri Aug 23 2019/

Finally had enough clarity to update the forecast for the rest of the
night through 12Z Saturday. A combined sea-breeze and outflow from
storms on the coastal plains pushed all the way to the Edwards
Plateau and Rio Grande Plains late this evening. This has re-
invigorated convection, but already the bump seems to be past the
peak and we expect convection to decrease over the next few hours.
That said, areas with storms in the vicinity now can expect a bit
more rain before midnight, then a fairly quick tapering off.
Otherwise, the rest of the forecast is in good shape, but we still
re-trended hourly variables through 12Z.

PREV DISCUSSION... /ISSUED 653 PM CDT Fri Aug 23 2019/

00Z Aviation forecast below.

Isolated to scattered SHRAs and TSRAs ongoing across portions of
South Central Texas this evening. Activity near and east of the I-35
corridor should diminish after sunset. Convection across portions of
the Hill Country and near the Rio Grande could persist longer into
the evening, before diminishing overnight. A few storms could produce
gusty winds. In addition, outflow from earlier storms, combined with
the sea-breeze boundary, is racing inland and producing strong wind
gusts at AUS, HYI, and BAZ and should arrive at SAT very shortly.
Wind gusts between 25-40 kts have been recorded with this boundary.
Outside of convection VFR conditions will prevail through the evening
and most of the overnight. A small area of MVFR ceilings may occur
between 09Z-15Z near the I-35 corridor.

PREV DISCUSSION... /ISSUED 250 PM CDT Fri Aug 23 2019/

SHORT TERM (Tonight through Saturday Night)...
Early afternoon water vapor imagery showed a few larger scale
features around the continental US with a compact upper low spinning
over Montana, Wyoming, and Idaho and a shortwave trough axis located
over the northwestern Gulf of Mexico. Additionally, regional VAD
wind profilers indicate that the mid-level trough that was evident
over West Central Texas on this morning`s radiosonde observations is
still lingering over West Central Texas. Visible satellite imagery
has shown an enhancement in the cumulus field in the vicinity of this
feature. Continued heating combined with weak lift from this trough
and residual surface boundaries from last night`s thunderstorms will
allow for deeper updrafts to develop through the remainder of the
afternoon hours and into the early evening. This will result in rain
chances focusing in two areas this afternoon: the Hill Country and
parts of the Rio Grande Plains, which are closer to the trough, as
well as the Coastal Plains as the sea breeze moves inland. Surface
dew point depressions around the region are close to 25 to 30 degrees
this afternoon and this relatively dry sub-cloud airmass will mean
that any strong thunderstorm will be capable of a gusty wind threat.
GOES Total Precipitable Water satellite imagery shows that
precipitable water values range from 1.6 to 1.9 inches across the
region this afternoon in a weakly sheared environment and
thunderstorms will also be slow-moving and capable of locally heavy

Regional radars shows a southward-moving outflow boundary nearing
the Interstate 20 corridor as well, which a few HRRR runs have
indicated may reach Central Texas before midnight tonight. Only
carrying a silent 10 percent chance of rain for this feature, but a
mid-evening update to increase rain chances for the Central Texas
counties may be needed should it hold together. Otherwise, storms
may linger into the the early morning hours across Val Verde County
given the proximity of the mid-level trough with a few streamer type
showers edging into the Coastal Plains by dawn. Redevelopment of
nocturnal stratus will again keep overnight lows elevated in the low
to mid 70s.

Broad mid/upper-level ridging spreads across California into the
Desert Southwest tonight as the weak mid-level trough axis remains
centered over Texas. As the closed low near Montana opens up and
crosses the Central Plains during the day Saturday, the weakness over
Texas gets pushed east of the region and and allows for ridging to
begin spreading back into the state Saturday night. This will mean
that isolated to scattered showers and thunderstorms will be possible
across most of the region during the late morning through early
evening hours on Saturday as convective temperatures are reached,
with greatest coverage along mesoscale boundaries either leftover
from storm`s today or the sea breeze. Forecast soundings continue to
indicate an inverted-V profile, indicating stronger cells on Saturday
will once again be capable of gusty winds. While a few storms may
linger into the evening hours Saturday across the Rio Grande Plains,
loss of heating will allow for most activity to dissipate with lows
again in the low to mid 70s.

LONG TERM (Sunday through Friday)...
With mid-level ridging building back into the region on Sunday,
temperatures will gradually get hotter Sunday through the mid-week
period. This will also suppress rain chances across most of the
region save for the sea breeze as it reaches the Coastal Plains. A
series of troughs crossing the Central Plains late week may attempt
to send a cold front into North Texas by late in the forecast, but
inconsistencies amongst medium range guidance precludes introducing
any kind of significant changes to the temperature or rain forecast
late week.


Austin Camp Mabry              78  99  78 102  78 /  10  20  10  10  -
Austin Bergstrom Intl Airport  77  98  78 101  77 /  10  20  10  10  -
New Braunfels Muni Airport     76  98  77 100  76 /  10  20  10  10  -
Burnet Muni Airport            75  98  76 100  76 /  10  20  10  -   -
Del Rio Intl Airport           78 102  79 104  80 /  20  10   0   0   0
Georgetown Muni Airport        77  99  78 101  78 /  10  20  10  10  -
Hondo Muni Airport             76 100  77 102  77 /  20  20  10  10  -
San Marcos Muni Airport        76  98  77 100  76 /  10  20  10  10  -
La Grange - Fayette Regional   77  98  78 100  78 /  10  30  10  20  -
San Antonio Intl Airport       78  98  79 101  78 /  10  20  10  10  -
Stinson Muni Airport           78  98  79 101  78 /  10  20  10  10  -




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