386
FXUS64 KEWX 231737
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1137 AM CST Mon Dec 23 2024

...New AVIATION...

.SHORT TERM...
(Today through Tuesday)
Issued at 158 AM CST Mon Dec 23 2024

Key Messages...

- High humidity and above normal temperatures, but little or no
chance of rain through midday Tuesday.
- Rain chances over Central Texas to increase by late Tuesday
afternoon.

A broad zonal pattern over TX might allow for some low level lift to
generate a few sprinkles today and Tuesday morning, but the finer
resolution models have trended slightly more stable for today. A
weak vorticity max moving over the area could generate a brief
streamer shower over the Coastal Prairies, but significant
measurable amounts of rainfall are not anticipated. Light to
moderate SE winds and continued deepening of the low level moist
layer could lead to a bit more coverage of mainly light fog late
tonight/Tuesday morning.

In the early morning hours sharpening vorticity over NW TX carves
out a clipper style upper trough to dig southeastward, leading to
greater moisture pooling over Central TX and possibly in a deep
enough layer to support a few daytime showers and perhaps an
isolated clap of thunder. A weak cold front will take shape over NW
TX and push close to our northern Hill Country counties by early
Tuesday afternoon, with the above normal temperatures and dew points
possibly supporting scattered, but still mainly shower coverage over
our NE counties in the afternoon.

Late in the day, the cold front and stronger PVA moves in closer to
Central TX to set up a better environment for early evening storms.
The NAM suggests more instability in the afternoon for the eastern
Hill Country, but we prefer the more stable and shallow moist layer
there with H925 to H850 winds more out of the SW to limit moisture
depth there through 00Z. This low level wind profile should change a
bit by the end of the day to allow for more dynamic lift to open up
further south along and east of I-35 after 00Z.

&&

.LONG TERM...
(Tuesday night through Sunday)
Issued at 158 AM CST Mon Dec 23 2024

Key Messages...

-Multiple weak weather systems are forecast to impact mostly eastern
 areas of our CWA with low chances for strong to severe thunderstorms
 Tuesday.

-Above normal temperatures continue throughout the period.

Starting off the long term period a cold front will be advancing
into eastern areas of our CWA with most Hi-Res and global models now
showing a broken line of convection impacting the Hill Country and
I-35 Corridor Tuesday evening and moving out quickly before sunrise.
The SPC has placed our eastern half of the CWA under a marginal risk
of severe storms. That being said there does look to be about
750-1000 J/kg of MLCAPE just ahead of this front that the storms
should they develop could take advantage of. Additionally, per SPC
and looking at models, effective shear in the 30-35kt range would be
present which isnt strong but it`s enough to cause some locally
severe wind gusts and severe hail. Add in temperatures that range
from the upper 70s to near 80 with dewpoints in the 60 to 65 degree
range and there is plenty of fuel for these storms to work with. The
caveat to this is that models have gone back and forth with this
event for days now. Didn`t feel confident enough to raise the pops
and capped them below 40 percent for most areas in case the front
washes out our completely misses us altogether as has been shown in
previous model runs. Should storms develop we aren`t looking at a
lot of rain with most ensemble guidance spitting out a few hundredths
to a tenth of an inch, however there could be higher amounts in any
thunderstorms that do develop. It should be noted that there is a
sharp cutoff for those areas that do see rain and storms to those
that don`t with the Austin metro area seeing a 30-40% chance whereas
areas in southern Bexar county southward could see little to no rain
at all. After the cold front moves through, Christmas day looks dry
and quite warm with temperatures a little cooler then Tuesday with
highs still in the lower 70s.

After the first system moves through our attention then turns to the
second system which looks to impact our area on Thursday. This
system looks to have a much better shot at affecting eastern areas of
our CWA for several reasons. The first as discussed prior is that
this system still will have some moisture to work with that is left
over from the prior system due to the weaker nature of the cold
front that tries to move through. Second, there is an attendant low
pressure that has a trailing cold front which would allow for more
dynamic forcing across the area triggering showers and thunderstorms.
Depending on where the closed low sets up will have a big impact on
what happens in our area. For right now it does seem that this system
will have more energy and forcing associated with it but its still
too early to determine any specifics at this time.

Finally, a third system approaches the area Friday into the weekend
this one looks promising as well but again its quite far into the
future so its best to wait until we get past this first system before
getting into any specifics at this time. One thing is certain we
definitely have turned the corner into a more progressive pattern for
at least the next several days. Regarding temperatures, highs for
most will range from the mid 70s to near 80 with lows in the upper
50s to low 60s throughout the forecast period.

&&

.AVIATION...
(18Z TAFS)
Issued at 1123 AM CST Mon Dec 23 2024

The eastern edge of the solid cloud deck is near the San Antonio area
and we expect the ceilings to become VFR by the start of this TAF
period. However, they could remain MVFR for around another hour. DRT
will remain MVFR until around 20Z. Then all airports will be VFR
through the afternoon and evening. Low clouds will redevelop late
tonight and all terminals will drop to IFR/LIFR by around sunrise
Tuesday. There is a slight chance for thunderstorms Tuesday afternoon
in the Austin area.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              75  62  76  55 /  10  10  30  30
Austin Bergstrom Intl Airport  76  62  77  56 /  10  10  30  30
New Braunfels Muni Airport     78  61  79  58 /  10  10  20  30
Burnet Muni Airport            73  60  72  52 /  10  10  30  20
Del Rio Intl Airport           76  58  75  52 /  10  10  10   0
Georgetown Muni Airport        73  62  74  53 /  10  10  40  30
Hondo Muni Airport             76  60  76  55 /  20  10  10  10
San Marcos Muni Airport        76  60  77  56 /  10  10  20  30
La Grange - Fayette Regional   76  60  78  57 /  20  10  30  40
San Antonio Intl Airport       76  63  76  58 /  20  10  10  20
Stinson Muni Airport           78  63  79  60 /  10  10  10  20

&&

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

$$

Short-Term...18
Long-Term...CJM
Aviation...05