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

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FXUS64 KEWX 101748

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1248 PM CDT Mon May 10 2021


Cold front has slowed almost to a halt today, visible on satellite
from northern Val Verde County across to just south of Blanco to San
Marcos to Giddings. The Storm Prediction Center upgraded locations
west of Kerrville to Hondo to Carrizo Springs to an enhanced risk
today primarily for the threat of large to potentially giant hail.
Although clouds have been stubborn along the Rio Grande north of
Eagle Pass today and the 18Z DRT special sounding still shows a
relatively substantial 850mb capping inversion, the atmosphere is
primed above that for scattered to numerous severe storms this
evening. Most models continue to show the inversion eroding away by
the early evening, although they could be a tad early with that given
the strong warming observed by the sonde. Could see some elevated
development even in the next 1-2 hours over the Edwards Plateau, with
the main show expected to be mainly in the 5-11pm time frame. The
expectation is that the vast majority of the severe risk today is
along and west of US-281 with a very low chance for a pop-up storm to
briefly become strong east.



CIGs are hovering just below MVFR thresholds at SAT this afternoon
but should lift to VFR for a time. AUS is seeing a brief clearing but
it isn`t expected to last. Scattered thunderstorm development late
this afternoon through the evening has the potential to impact
DRT/SAT/SSF but confidence is low in direct impacts for San Antonio,
thus carrying VCTS there for now. Deteriorating flight conditions
return tonight with IFR by 03z at AUS and MVFR at DRT/SAT/SSF by
03-05Z. SAT/SSF could see IFR as early as 09/12Z but confidence too
low to include at this time. Somewhat better shower and thunderstorm
coverage is expected late tonight near DRT and then by the afternoon
hours Tuesday at the I-35 sites, details to be refined.


PREV DISCUSSION... /ISSUED 248 AM CDT Mon May 10 2021/

SHORT TERM (Today through Tuesday)...
With the presence of a stalled surface boundary, there will be a
wide range of temperatures across our area. Movement of the line
could mean more than a few degrees depending on side you are on. In
our northern counties, highs only in the mid to upper 70s while the
southern counties and Rio Grande Plains reach over 100 degrees.
While this boundary meanders across South Central Texas, a mid-level
shortwave approaches from the west. Daytime heating near the Rio
Grande should provide enough destabilization while the surface
boundary provides the convergence. Initial development of strong to
severe storms will likely be west of the US/Mexico border and
movement south and east is expected. A generous amount of CAPE in
this region with values of over 4000 J/kg. Lapse rates across the
area are steep enough to support very large hail in the right storm.
Convection could be ongoing into the overnight hours with the severe
potential lessening after sunset. SPC has the area highlighted in a
Slight risk for the western half of the area up to San Antonio, then
marginal eastward.

With features still unsettled, more showers and thunderstorms await
on Tuesday. With the lingering front now sagging further south
providing the lift for moisture continuing to flow in and over the
front, showers and thunderstorms will spread throughout the day. SPC
has the entire area highlighted for Marginal risk Tuesday with hail
and wind being the main threat, especially in areas that may get
some breaks in the clouds to allow for more heating.

LONG TERM (Tuesday Night through Sunday)...
A weak mid level impulse riding over the frontal surface provide
upward forcing for showers and thunderstorms Tuesday night through
Wednesday evening. Although PWs decrease to 1.1 to 1.5 inches, these
are still above normal. The threat of locally heavy rains lingers.
Some flooding is still possible, especially in areas that received
heavy rains today through Tuesday. Some shear and instability remains
in the mid levels. Cannot rule out isolated strong storms with hail.
Cold advection underneath cloudy and rainy skies makes for well
below normal temperatures and have continued the trend of lowering
high temperatures for Wednesday.

As the mid level impulse moves away, forcing wanes and moisture
continues to decrease Wednesday night into Thursday. Showers and
thunderstorms gradually end from north to south. Fair weather is
expected on Friday. Mid level impulses move over our area bringing
chances of showers and thunderstorms for Saturday into Sunday. The
ECMWF remains the most aggressive on rainfall with the GFS and CMC
much less. As a result, have gone with the blended POPs for now.
A slow warming trend back to near normal is expected.


Austin Camp Mabry              62  73  61  69  59 /  40  90  70  60  20
Austin Bergstrom Intl Airport  63  75  61  69  58 /  40  80  70  60  20
New Braunfels Muni Airport     65  77  62  72  59 /  40  80  70  60  20
Burnet Muni Airport            59  71  57  66  57 /  50  90  50  50  20
Del Rio Intl Airport           69  81  66  75  63 /  40  60  50  70  30
Georgetown Muni Airport        61  72  59  67  57 /  50  90  60  50  20
Hondo Muni Airport             66  80  64  74  59 /  50  80  60  60  20
San Marcos Muni Airport        64  76  61  70  58 /  40  80  70  60  20
La Grange - Fayette Regional   68  81  64  72  61 /  40  70  80  70  20
San Antonio Intl Airport       66  78  63  71  61 /  40  80  70  60  20
Stinson Muni Airport           68  81  65  73  62 /  40  70  70  60  20




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