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

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FXUS64 KEWX 211922

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

.SHORT TERM (Tonight through Thursday Night)...

Weak upper troughing persists as we maintain the southerly flow in
the low levels. While fair weather and mostly sunny skies are
expected during the day today, tonight clouds increase again as the
moisture continues to flow into the area. Chances for showers have
lowered for Thursday. While there may be a stray shower in the area,
there is enough uncertainty and low enough chances to leave it out
of the forecast. Overnight lows tonight will be much like last
night, with some high 60s in the Hill Country and low 70s elsewhere.
Highs on Thursday will be also be almost a carbon copy of today`s
highs with mid to upper 80s across the area. Winds stay generally
light and out of the southeast.


.LONG TERM (Friday through Wednesday)...

We`ll start the long term on Friday with another day of above normal
temperatures and high humidity, but a cold front will be knocking on
our doorstep by the afternoon and temperatures will begin to fall
quickly through the evening over northern portions of the region.
After highs in the 80s to near 90, lows will drop into the low 50s
north and low to mid 60s south Friday night. A few isolated showers
and maybe a thunderstorm or two could impact primarily our northern
counties in the afternoon and evening behind the front, but chances
are slim.

After a beautiful Saturday with highs in the mid 70s to mid 80s and
mostly sunny skies, flow will quickly return to southerly on Sunday
and warm us back into the mid 80s to mid 90s. Our attention then
turns to the next potential front expected to drop south towards the
region Monday as a deepening positively tilted trough digs
southeastward through the western CONUS.

While model divergence remains large and suggests there`s still a
chance the front slows and/or stalls on approach to the gulf,
ensemble guidance is leaning in the direction of FROPA late on
Monday which could bring the coldest airmass of the fall thus far.
If the front slows enough or does stall, highs Monday would be
warmer than currently forecast and could potentially approach record
values with the assistance of compressional warming. If the front
passes during the afternoon Monday as currently forecast, Tuesday
morning lows as cold as the mid 30s would be possible over the Hill
Country. Given the slow-down in the mid-level trough, there`s
unlikely to be enough support for the near-freezing temperatures
depicted in the deterministic GFS, which sits right near the bottom
of the GEFS envelope. With cloud cover expected, there will be
little radiative cooling and advective processes will dominate.
Keeping in mind that the new GEFSv12 was designed to be more
dispersive and better represent extreme events, we do believe the
coldest solutions to be less realistic at this time. Have opted to
keep the NBM as the official forecast for now, but the point is that
this is not a WYSIWYG forecast for Monday and beyond. As much as I`d
love for this to be a "target of opportunity" to improve on the
initialization, there`s just too much uncertainty at 6 days out to go
either way with any confidence. We should have a little better
handle on things in a couple of days once we get into the NAM time
frame, as the NAM has done a pretty good job with these shallow, cold
airmasses this and every year.

Rain chances in the pre- and immediate post- frontal environment may
not be all that impressive, although are nonzero across the northern
half of the region Monday. These chances will increase to near 40
percent Tuesday and Wednesday of next week as the parent trough
approaches, which may or may not cut off and slow further before it
reaches us as the northern and southern streams disconnect. Most of
the forcing for widespread and appreciable rainfall is forecast to
remain across north Texas, so this is unlikely to be a drought-buster
type of event. WPC QPF through 12Z next Wednesday is depicting
mainly less than a quarter of an inch. Nonetheless, this system will
provide the best chance for much needed beneficial rainfall since


.PREV DISCUSSION... /ISSUED 1220 PM CDT Wed Oct 21 2020/

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.


Austin Camp Mabry              69  86  69  84  57 /   0  -    0  20  -
Austin Bergstrom Intl Airport  68  87  68  85  57 /   0  -    0  10  -
New Braunfels Muni Airport     70  89  70  88  60 /   0  -    0  -    0
Burnet Muni Airport            68  85  68  78  54 /   0   0   0  20  -
Del Rio Intl Airport           69  89  68  89  62 /   0  -    0  -   -
Georgetown Muni Airport        67  86  68  83  54 /   0   0   0  20  -
Hondo Muni Airport             67  89  68  89  60 /  -   -    0  -   -
San Marcos Muni Airport        68  87  68  86  58 /   0  -    0  10  -
La Grange - Fayette Regional   69  87  70  87  60 /  -   10   0  -   -
San Antonio Intl Airport       70  87  70  87  60 /  -   -    0  10  -
Stinson Muni Airport           69  87  69  87  61 /  -   -    0  -   -




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