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

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FXUS64 KEWX 190302

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1002 PM CDT Tue Sep 18 2018

Just sent a forecast update to remove low PoPs for western Val Verde
County late tonight and early Wednesday, as diurnal convection has
shut down for the night and return Gulf flow should not result in
more than light drizzle if anything at all. Otherwise, we re-trended
the hourly forecast values through 12Z to reflect expected trends.


.PREV DISCUSSION... /ISSUED 639 PM CDT Tue Sep 18 2018/

00Z Aviation forecast below.

VFR conditions through the evening hours. Stratus is forecast to
develop from DRT-SAT and north into the Hill Country 07Z-10Z
resulting in IFR ceilings. HRRR indicating the stratus could advect
north to near or just south of the AUS area around daybreak. Current
SCT010 for AUS reflects uncertainty, but if trends continue northward
BKN IFR or MVFR ceiling may be needed for AUS in the 06Z TAF cycle.
The stratus will gradually scatter out 14Z-17Z, perhaps a little
longer near the Rio Grande. S to SE winds diminishing to under
10 kts tonight.

PREV DISCUSSION... /ISSUED 303 PM CDT Tue Sep 18 2018/

SHORT TERM (Tonight through Wednesday Night)...
The latest water vapor imagery shows an upper low centered in the
northwest Gulf of Mexico, with broad cyclonic flow in the mid and upper
levels across roughly the southern half of Texas. In the low-
levels, weak high pressure was located over southeast Texas with
southerly winds in place across our region. Late afternoon
temperatures across the region were generally in the 80s with a few
readings in the lower 90s.

For the remainder of this afternoon and early evening, we will maintain
a low chance for convection along the Rio Grande. The latest hi-res
models are not very aggressive in coverage and will keep rain chances
limited to 20%. Most activity is expected to diminish with daytime
heating, although a few showers can`t be ruled out during the early
morning hours as the low-level jet strengthens. Elsewhere, look for a
rain-free forecast tonight with some patchy fog developing after
midnight along and east of the I-35/I-37 corridor. The coastal plains
will be favored for lower visibilities during the overnight hours
into early Wednesday morning as winds will be lightest here.

On Wednesday, the overall pattern will change little as the upper low
in the northwest Gulf drifts northward. We still expect some isolated
showers and thunderstorms to develop, mainly in the afternoon hours
along the Rio Grande. The latest suite of hi-res models do not show
much coverage of showers and storms and we will limit rain chances to

LONG TERM (Thursday through Tuesday)...
On Thursday, the weather pattern will begin to change as the subtropical
high shifts eastward and strengthens over the eastern U.S., while a
broad trough approaches from the west. The latest round of model data
continues to advertise a good chance of rain for south central Texas
during the latter half of the week. The remnants of a weak tropical
disturbance in the eastern Pacific are still not handled too well by
the models. However, it does appear we can expect some increase in
moisture from the Pacific along with southerly flow in the lower and
mid-levels, leading to increasing moisture from the Gulf of Mexico.
Rain chances on Thursday will initially be favored across the Rio
Grande plains where low-level upslope flow and a weak upper
disturbance moving in from the west will be found. As weak upper
disturbances continue to filter in from the west, rain chances will
spread eastward and increase on Friday and Saturday. The models
continue to show precipitation will be fairly widespread and have
also increased rainfall amounts in the latest MOS data. With a lack
of a well-defined surface feature, it will be difficult to pinpoint
which areas will see the heaviest rains as we head into late this
week and the upcoming weekend. For now, we have increased rain
chances across all areas on Friday and Saturday. If subsequent model
data remains consistent, we will need to increase the chance of rain
for all areas on Saturday, with the focus for rainfall expected to
shift eastward to along and east of the I-35 corridor on Sunday. We
have included the mention of locally heavy rainfall in the Hazardous
Weather Outlook for Thursday through the weekend.

For early next week, we should see a gradual decrease in rain chances
with only a very minimal decrease in moisture. Areas east of I-35
will remain favored for some afternoon seabreeze convection on Monday
and Tuesday. The medium range models also show potential for an
inverted trough moving in from the Gulf early next week, but differ
on the timing.


Austin Camp Mabry              74  92  74  88  75 /   0  -   -   30  20
Austin Bergstrom Intl Airport  72  92  73  89  75 /   0  -   -   30  20
New Braunfels Muni Airport     72  90  73  88  74 /   0  -   10  30  30
Burnet Muni Airport            71  90  72  86  73 /   0  -    0  30  20
Del Rio Intl Airport           74  87  74  85  74 /  10  20  20  40  50
Georgetown Muni Airport        73  92  72  89  74 /   0  -   -   30  20
Hondo Muni Airport             72  88  73  88  74 /   0  -   10  40  50
San Marcos Muni Airport        72  91  73  88  74 /   0  -   10  30  30
La Grange - Fayette Regional   74  93  74  90  75 /   0  10  -   30  20
San Antonio Intl Airport       73  89  74  88  75 /   0  -   10  30  40
Stinson Muni Airport           74  90  74  89  76 /   0  -   10  30  40




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