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000
FXUS64 KEWX 211720
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1220 PM CDT Wed Oct 21 2020

.AVIATION...
MVFR ceilings are continuing to scatter out and the area is mainly
 fair weather clouds with some TCU and area showers near SAT. Those
showers should diminish in the next area and leave the terminal
unaffected. Tonight, MVFR ceilings return for all sites then becoming
IFR for SAT and AUS. SSF may also reach IFR, but have opted for the
optimistic and may need to adjust in a later issuance. Winds will be
light and out of the southeast through the TAF period.

&&

.PREV DISCUSSION... /ISSUED 632 AM CDT Wed Oct 21 2020/

UPDATE...
Please see the 12Z aviation forecast discussion below.

AVIATION...
Low clouds continue to expand across the region early this morning.
Overall, no significant changes have been made to the forecast, with
predominant, low-end MVFR cigs expected to continue through this
morning. We did extend the TEMPO groups for IFR cigs a little
further in time at SAT and SSF based on recent obs and incoming data.
We have also removed the TEMPO group for IFR cigs at AUS. Low clouds
continue to expand westward and DRT can still expect MVFR through
this morning. Improvement at all sites is in store late morning and
early afternoon as clouds lift and scatter. For late this evening
into early Thursday morning, another round of low cloud development
is highly likely. For now, we will mention MVFR beginning 06Z for the
I-35 sites. A fair amount of the numerical guidance members suggest
IFR could develop within a few hours of MVFR cigs. Our confidence is
not that high this far out in time, but this trend will certainly
need to be monitored.

PREV DISCUSSION... /ISSUED 604 AM CDT Wed Oct 21 2020/

UPDATE...
We have updated the forecast to add a mention of patchy fog across
the coastal plains through mid-morning. Rain chances for this morning
have also been expanded southward slightly to cover the light showers
now developing over Atascosa county.

PREV DISCUSSION... /ISSUED 423 AM CDT Wed Oct 21 2020/

SHORT TERM (Today through Thursday)...
A fairly broad and weak upper level trough will remain intact across
northeastern Mexico and west Texas through Thursday. This trough
along with daytime heating and adequate low-level moisture will
result in a low chance for showers and thunderstorms across portions
of south central Texas today and Thursday. For this morning, most of
the Hill Country, areas along the I-35 corridor and into the coastal
plains could see some isolated showers. Rainfall amounts will be very
localized, with amounts generally at or below one-tenth of an inch.
Highs today will be in the lower 80s to lower 90s across the region.
Persistent, moist southeast flow in the lowest 5000 feet of the
atmosphere will yield plenty of cloud cover into the early afternoon,
with decreasing cloudiness for the late afternoon through evening
hours. Overnight lows will be quite warm for mid October, ranging
from the mid 60s to lower 70s.

Similar weather is in store for Thursday with some isolated morning
showers for the Hill Country, I-35 corridor and coastal plains. We
can`t rule out an isolated thunderstorm across the coastal plains in
the afternoon and have included a low chance for this in the latest
forecast. Highs on Thursday will again range from the lower 80s to
lower 90s.

LONG TERM (Thursday Night through Tuesday)...
Clouds will increase overnight late Thursday night into Friday
morning with lows in the mid 60s to lower 70s. As the morning period
goes by, a cold front is forecast to push across central Texas and
then moves across the Hill Country around mid-day or early
afternoon. Most model guidance has the frontal boundary pushing
across the Hill Country/Edwards Plateau area between 10 AM to 1 PM
on Friday with the exception of the SREF, which brings it in late in
the afternoon. Also, the same earlier models, bring convection along
the boundary for parts of the Hill Country and Edwards Plateau on
Friday afternoon. The convective signal goes away with the loss of
daytime heating.

Looking at the area forecast soundings, this is a shallow boundary
with a slightly cooler air mass behind it. If the front pushes over
the area as expected (around noon time Friday), there is a good
chance for the highs to occur around that same time before dropping
to the mid 70s across the Hill Country in the mid to late afternoon.
Overnight lows (Saturday morning) will get down to the lower 50s
across the Hill Country and 60s elsewhere.

The weekend looks good with dry weather conditions and plenty of
sunshine for the afternoon period. Highs on Saturday a bit cooler
between the upper 70s to upper 80s with a warming trend for Sunday
with the return of southerly flow with highs in the mid 80s to lower
90s across the Rio Grande.

Big changes are expected for early next week as a strong cold front
pushes across the area on Monday. Global models agree on the frontal
passage across South Central Texas but when it comes to how cold the
airmass will be then there is a huge disagreement. For example,
Monday`s highs for Austin is 64 degrees based on GFS but 88 degrees
for the ECMWF. What about on Tuesday? Any better? So here we go,
Tuesday`s highs for Austin is 46 degrees based on GFS and 79 degrees
for the ECMWF. What about the NBM solution? So, let`s look at
Monday`s highs for Austin: 89 degrees based on the NBM solution.
Having said that, we took a middle of the road approach for this
forecast package and hope for the models to become better aligned in
future runs as far as temperatures go.

The one thing these models have a good handle on is the potential
for rain early next week across most areas especially over the
eastern two-thirds of South Central Texas. Stay tuned as we modify
the extended forecast for next week as the strong cold front nears
the local area.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              86  69  86  69  84 /  -    0  -    0  20
Austin Bergstrom Intl Airport  87  68  87  68  85 /  -    0  -    0  10
New Braunfels Muni Airport     89  70  89  70  88 /  -    0  -    0  -
Burnet Muni Airport            85  68  85  68  78 /   0   0   0   0  20
Del Rio Intl Airport           89  69  89  68  89 /   0   0  -    0  -
Georgetown Muni Airport        86  67  86  68  83 /   0   0   0   0  20
Hondo Muni Airport             89  67  89  68  89 /  10  -   -    0  -
San Marcos Muni Airport        88  68  87  68  86 /  -    0  -    0  10
La Grange - Fayette Regional   89  69  87  70  87 /  -   -   10   0  -
San Antonio Intl Airport       87  70  87  70  87 /  10  -   -    0  10
Stinson Muni Airport           87  69  87  69  87 /  10  -   -    0  -

&&

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

$$

Short-Term/Aviation...YBVP
Long-Term...KCW
Decision Support...Runyen