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

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS64 KEWX 290409

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1109 PM CDT SAT MAY 28 2016

Complex of storms continues to evolve into a possible overnight
heavy rain threat and continued threat of severe storms. Extended
the severe thunderstorm watch for two hours and added a row of
counties to the east to include Comal and Bexar Counties until



Complicated forecast evolution for the overnight period with the
ongoing thunderstorm complex across the northwest CWA. Convection
was kicked off this afternoon with daytime heating in an area of
surface moisture confluence. Some of the storms became severe,
but it appears at the present time that the main threat going
forward will be heavy rainfall. Forecast soundings do show some
de-coupling overnight, but not enough to really increase the
nocturnal cap to help suppress convection. There is little upper
forcing to really support the convection, but since it is now
ongoing, the storms will be able to continue as long as the cold
pools continue to move out from under the convection and help to
sustain and support new updrafts. This seems to be continuing
just fine at the present time as evident by continued cloud tops
on IR of near -75C.

The main question now is how long the storms will continue and
what the overall movement will be. the KEWX VAD wind profile shows
deep south/southeasterly flow of 20 to 30 knots in the lower 7 kft
of the atmosphere with model guidance slightly increasing the
wind speeds. This should help continue to feed the MCC with
moisture and help with some weak lift up the escarpment. The HRRR
has had a tough time with the placement of the current convection
but does show some continued movement of a potential MCC to the
south/southeast. This helps increase confidence of a prolonged
system. Forward propagation vectors do show movement to the east,
but we have not seen that at the present time.

Current thinking is that the system should sustain itself over the
next few hours before some slow weakening should occur. Upped the
pops across the west-central CWA to likely and mentioned locally
heavy rainfall for this area to continue the trend of a slow-
moving system to the SSE. Increased PoPs to the east a bit to
account for any possible eastward movement and to account for
lighter activity forming to the east of the main thunderstorm


AVIATION.../00z Update/
Concerns this forecast will be convection this evening and then
the development of MVFR/IFR cigs. Currently isolated showers and
thunderstorms have developed west of I-35. Expecting to see more
development this evening. If the convection does develop and can
last long enough we may see some approach the I-35 sites after
06z. prior to that showers are possible and have included a VCSH
group for KSAT/KSSF. Convection west of KDRT may get close to Del
Rio but timing is not certain and for this reason I did include a
VCTS through 02z. Onset of MVFR cigs likely to be a couple hours
sooner tonight and have all the I-35 terminals seeing the cigs
lower starting 04z- 05z. After 07z-08z should see IFR cigs along
I-35. KDRT will see MVFR cigs starting around 08z with the IFR
cigs expected around 12z. VFR conditions are expected after 17z-
18z. All site have the potential to see fog due to the wet ground.
Lowest visibilities likely at KAUS (2SM) with all other terminals
remaining in the 4sm-6sm range. E/SE winds near 10 knots tonight
then SE 10-15 knots after 15z Sunday. KDRT will see wind gusts to
around 20 knots after 18z through sunset.


SHORT TERM (Tonight through Sunday Night)...
At 230 PM, South Central Texas surface analysis showed
temperatures ranging from the mid 80s to low 90s with dewpoints in
the low to mid 70s, showing the entire CWA as quite moist and
unstable. North and west of the CWA a dry line was positioned from
just west of Sanderson to Sheffield up to Sweetwater. Latest
RAP/HRRR/LAPS soundings show capping eroding west of a line from
Uvalde to Junction. Weak capping is holding on in SAT/AUS per the
same forecast soundings. Aircraft soundings out of KSAT also show
weakening but still decent cap. With convective temperatures right
around 90-92 degrees and surface temperatures near 90 south of the
Plateau...believe convective initiation will take place in the
next 1-2 hours within the slight risk area SPC has annotated.

With SBCAPE values very high again and DCAPEs AOA 1000 j/kg, very
large hail and wind gusts up to 60 mph will be the main threat.
While the upper level support is lacking currently due to broad
ridging overhead...a shortwave disturbance is progged to enter the
Big Bend region after 7PM. This weak upper level support coupled
with the high instability, decent shear, steep lapse rates, and
theta-e convergence along the dry line, think the slight risk area
is laid out well for this afternoon and evening. Thinking the
tornado threat is rather low but 0-3 km SRH values are in the
150-200 range this evening west of I-35 and LCLs are lowest south
of the escarpment (Winter Garden), so cannot rule out one in this

Thinking storm coverage should wane before midnight as we lose
instability. Tomorrow looks to be a very similar pattern with
afternoon/evening convection along the dry line out west again.
SPC has included the same general area in a slight risk with the
same threats as well for Sunday.

LONG TERM (Monday through Saturday)...
A southwest flow regime will set up for the week with weaker
shortwaves impacting the moist air mass over the region through
Tuesday. Included 30-40 PoP values for both Monday and slightly
higher Tuesday as these pass over.

The next significant storm system for South Central Texas looks to
be on Wednesday ahead of a strong cold front. Models are
indicating 1-3 inches of storm total rainfall associated with this
system and with the moist soils from the last few days heavy rain
event, flash flooding would be the main concern Wednesday.
However, the progression of the cold front looks fast enough at
this time that training shouldn`t be an issue but due to the
antecedent conditions, the flash flood threat will be possible

Late in the week, the cold front should result in a drier and
cooler air mass at least through Saturday. Temperatures should be
below normal, with highs in the 80s for the first week of June.


Austin Camp Mabry              73  87  71  85  70 /  50  30  30  20  20
Austin Bergstrom Intl Airport  72  87  71  85  70 /  50  30  30  20  20
New Braunfels Muni Airport     74  88  71  86  71 /  60  30  30  20  20
Burnet Muni Airport            71  85  69  84  69 /  50  30  30  30  20
Del Rio Intl Airport           74  89  73  87  71 /  50  30  30  30  40
Georgetown Muni Airport        73  85  69  84  69 /  50  30  30  30  20
Hondo Muni Airport             73  89  72  87  71 /  60  20  20  30  40
San Marcos Muni Airport        74  86  71  86  69 /  50  30  30  20  20
La Grange - Fayette Regional   74  87  72  86  70 /  30  20  20  20  20
San Antonio Intl Airport       75  88  72  86  72 /  60  20  20  30  20
Stinson Muni Airport           74  89  73  87  73 /  60  20  20  30  20




Public Service/Data Collection...30 is the U.S. government's official web portal to all federal, state and local government web resources and services.