613 
FXUS64 KEWX 091137
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
637 AM CDT Sat Oct 9 2021

.AVIATION...
VFR conditions will continue through the morning and into the day
today. Some brief patchy fog has formed along the Coastal Plains, but
indications are that this will stay just to the east of the terminals
through the morning hours. Winds will pick up out of the south this
afternoon between 08 and 14 knots, and be gusty at times at DRT. With
plenty of Gulf moisture returning to the area think at least MVFR
ceilings are possible in most areas tomorrow morning beginning some
time between 06z and 09z. Models are indicting IFR at the San Antonio
terminals, but not confident enough yet to prevail IFR. For now
included a SCT007 for SAT/SSF. Some indications are that the MVFR
will make it all the way out to DRT by daybreak on Sunday as well.
With winds becoming elevated not super confident in this so have only
mentioned a SCT025 at DRT for Sunday AM. 

&&

.PREV DISCUSSION... /ISSUED 256 AM CDT Sat Oct 9 2021/ 

SHORT TERM (Today through Sunday)...

Enjoy the warm and sunny weekend because big changes are on the way 
starting Sunday night and continuing for the middle to late part of 
next week as a pair of cold front arrive. In the short term though 
the upper level ridge will maintain its grasp on South Central Texas 
today before being forced south as a potent upper level trough 
arrives late Sunday afternoon into Sunday night. While the main 
impacts from the trough will be felt starting Sunday night (in the 
long term period) the trough will be approaching the Texas Panhandle 
by Sunday afternoon. At the surface the ridge to the east will 
continue to produce southerly winds across the area hastening the 
return of Gulf of Mexico moisture. This will result in the return of 
morning low clouds for Sunday. As the surface low pressure develops 
over north Texas late Sunday the pressure gradient ahead of it will 
tighten with the high to the east producing some gusty southerly 
winds during the afternoon hours. Temperatures will also be on the 
increase with the increasing moisture. Today will be another day in 
the lower 90s, but tonight rather than lows in the low to mid 60s 
(as we are seeing tonight), forecasted lows are roughly 5 to 8 
degrees warmer in the mid to upper 60s. Highs on Sunday will also 
follow this trend topping out in the low to mid 90s. Highs may even 
be a few degrees warmer depending on the progress of the front and 
compressional warming ahead of it. By late Sunday afternoon dew 
points will be in the 70s and the strong upper trough will be moving 
into North Texas. This will prime the atmosphere for the arrival of 
the front Sunday night.

LONG TERM (Sunday Night through Friday)...

Strong agreement in the model guidance with the placement of the H5 
trough axis over the TX Panhandle to begin the long term. Sunday 
evening, the breezy southerlies will begin to subside ahead of the 
arrival of a cold front associated with the system. The front will 
begin to move in from the NW right at the start of the period, but 
model soundings indicate CIN that will gradually erode away in the 
00Z-06Z time period. Showers and storms should develop as the cap 
breaks, likely entering our Hill Country counties around 10pm give 
or take 1-2 hours, then spreading south and east through the 
overnight then exiting the Coastal Plains after sunrise Monday 
morning. Even after midnight, CAPE values are forecast to exceed 
1500J/kg and deep layer shear, though more impressive well to our 
north, will be sufficient for organized, potentially rotating 
storms. A storm or two will have the potential to become severe with 
large hail and/or damaging winds possible, with the new SPC Day 2 
outlook expanding the Marginal Risk area to include locations north 
of Utopia to New Braunfels to La Grange. Precipitation amounts won't 
be too impressive, with most areas seeing less than half an inch but 
locally higher amounts up to 2" cannot be ruled out. 

Per NAM, which typically handles cold fronts well, we could be in 
for a cooler day Monday behind the front than is currently forecast 
and so I've hedged in that direction from the still relatively warm 
NBM. However, even if the cold front does clear south-central TX, 
it'll turn right back around as a warm front and pass back to our 
north Monday night. Could be some isolated streamer shower activity 
in the warm sector but have left mention out of the forecast for 
now. 

Tuesday will be warm, humid, and a bit breezy once again with 
southerly winds gusting to 25 and potentially 30 mph at times. The 
next trough, much deeper than the first, will be located near the 
Four Corners at 18Z Tuesday. It's progression appears slightly 
slower than the last few model runs, but confidence is beginning to 
increase in it's track as it deepens and turns to the NE and 
eventually N, passing over the Dakotas on Wednesday and Wednesday 
night. Here in TX, some isentropic lift in the warm sector could 
lead to precipitation development over the Rio Grande Plains early 
Wednesday, but chances for showers and storms will increase and
spread east through the day, continuing through the end of the 
period as the frontal boundary becomes nearly stationary. With 
southeasterly flow in the BL tapping into gulf moisture and SW flow 
aloft bringing additional moisture from the Pacific coincident with a
likely EPAC tropical system coming onshore somewhere over MX, 
confidence continues to increase in very anomalous PW potentially as 
high as 2.3". Ensemble mean values have increased run to run and now 
exceed 2" for parts of the area Wednesday night, and in combination 
with low level convergence along the front, divergence in the RER of 
a SW/NE oriented jet aloft, and PVA ahead of a secondary trough axis,
periods of showers and thunderstorms will be likely and locally 
heavy rainfall could be a concern in the Wed-Fri period. Details of 
timing and placement of the greatest risk will continue to be refined
over the coming days. Operational GFS remains more bullish on 
moisture and forcing than most guidance and impacts are still not a 
guarantee with many ensemble members still outputting manageable, 
drier solutions. Will keep POPs capped at 50 through the period until
things become clearer. 

Ridging will build into the western US as we head into next weekend, 
finally allowing the pattern to become more progressive and pushing 
the frontal boundary through the region Friday night or Saturday. We 
should see conditions dry out behind it over the weekend and cooler 
air should finally move in with highs likely in the 70s.

PREV DISCUSSION... /ISSUED 1234 AM CDT Sat Oct 9 2021/ 

AVIATION...
Another night of VFR conditions is expected tonight through tomorrow
as southerly winds continue across the I-35 terminals with
southeasterly winds at DRT. Moisture continues to stream into the
area with southerly winds picking up between 10 and 14 knots 
tomorrow at all TAF sites. This will allow for overnight stratus to
return for Sunday morning. While future TAF packages will nail down
the timing and the height of the ceilings, have gone ahead and
introduced low end MVFR at the two 30 hour TAF sites for Sunday
morning. 

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              90  70  92  69  86 /   0  -   -   60  -  
Austin Bergstrom Intl Airport  89  68  92  69  86 /   0  -   -   60  -  
New Braunfels Muni Airport     89  68  93  70  86 /   0  -    0  50  -  
Burnet Muni Airport            89  67  90  63  84 /   0  -    0  50  -  
Del Rio Intl Airport           93  69  95  66  91 /   0   0   0  10   0 
Georgetown Muni Airport        90  69  91  65  85 /   0   0  -   50  -  
Hondo Muni Airport             91  68  95  69  89 /   0  -    0  30  -  
San Marcos Muni Airport        89  68  93  69  86 /   0  -   -   50  -  
La Grange - Fayette Regional   90  70  91  72  86 /   0  -   10  60  20 
San Antonio Intl Airport       90  71  93  72  87 /   0  -   -   40  -  
Stinson Muni Airport           91  71  95  73  88 /   0   0   0  30  -  

&&

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

$$

Short-Term/Aviation...Treadway
Long-Term...KCW