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

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FXUS64 KEWX 310548

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1248 AM CDT TUE MAY 31 2016


Mesoscale models show fair agreement on the next round of rain
forming around DRT by 09Z and tracking east toward I-35 during the
late morning hours. With radar loops showing disorganized clusters
of convection over Mexico and Far W TX, will show some VCTS and
update in the next few hours to add tempo or prevailing groups once
a distinct convective trend takes shape. The atmosphere remains
quite unstable and is capable of developing storm clusters at all
hours of the TAF periods, making it difficult to pinpoint storm
timing without some indication of a surface boundary. Aside from
these uncertainties, the area TAFs continue to dip into IFR skies
generally between 09Z and 16Z with a few hours of MVFR skies on
each side. Wind should remain mostly below 12 knots except near



Made few minor changes to the weather grids to reduce PoPs over
parts of the Rio Grande based on area radar trends and HiRes
models solutions. Still expecting scattered showers and isolated
thunderstorms across the Big Bend and northeast Mexico to push
eastward late tonight continuing overnight. New rainfall amounts
out west could range from few hundredths to one quarter inch with
up to one half inch over isolated spots. Widespread flash
flooding conditions are not expected for this period, however,
some local roads may end up with pounding of waters.


VFR conditions are prevailing at the TAF sites this evening. A
return to MVFR and IFR is expected overnight. While there is a
chance of storms at all sites at some point this valid period,
will try to only mention storms in the TAFs when the probability
is high enough to warrant the inclusion of activity. Think chances
will warrant a mention of VCTS for Del Rio this evening for
possible activity moving in from the west. VFR is expected to
return tomorrow afternoon. Southeasterly flow is expected to
continue through tomorrow.


SHORT TERM (Tonight through Tuesday Night)...
With the passage of the morning MCS, the CWA has enjoyed a period
of dryness that may be few and far between beyond today. There
currently is elevated convection ongoing out in West Texas which
is being largely being helped by a subtle shortwave at 500 mb.
While this activity could make it east into our CWA, the current
atmosphere still has over 100 J/KG of CIN and dewpoints in the low
60s, which is about 10 degrees less than in previous days. While
some destabilization is ongoing and capping will weaken,
confidence in significant severe or heavy rain activity reaching
the CWA is quite low. Having said that, some showers and storms
will probably impact the Rio Grande Plains and plateau areas and
result in measurable rain and latest HRRR does indeed show a sub-
severe complex approaching from the west. As a result...lowered
QPF quite a bit but kept the 40-50 percent PoP chances from the
previous forecast.

For Tuesday, while hi-resolution models are quite dry for most of
the day, synoptic models produce QPF by mid to late afternoon and
increase coverage into the overnight hours. Expect isolated to
scattered shower activity as instability increases and as low
level jet increases into the overnight hours, coverage should
increase across much of the CWA.

LONG TERM (Wednesday through Monday)...
Another possible MCS may occur overnight Tuesday and exit in the
morning hours allowing for a brief lull in rainfall until around
noon when the dynamics of the upper low begin to influence the
region. There has been the prospect of a cold front passage the
last few days through the CWA but now it seems this front will
stall well north of the area, which may be good news as a lack of
focused lifting prohibits the prospect of organized convection.
However...PWATs 1.8-2 inches are expected and with good upper
level support...think that at least isolated flash flood potential
will exist for the whole CWA, especially in locations already hit
with multiple inches of rain over the last 4-5 days.

The upper level pattern continues to slow down in its progression
through the state in the late week period. As a result, multiple
periods of heavy rainfall will be possible with the high PWATs and
broad, deep upper influences. GFS/EURO still disagree on the
evolution of the low as it exits to the east...or south even if
the EURO is to be believed.

So in the end, agree with the previous forecast that Flash Flood
Watches will be needed as early as Tuesday night which may need to
be an extended watch due to the periods of possible heavy rainfall
for the next 48 hours...or through Thursday.


Austin Camp Mabry              70  82  68  81  67 /  40  70  60  70  60
Austin Bergstrom Intl Airport  69  82  68  80  67 /  40  70  70  70  70
New Braunfels Muni Airport     70  83  68  81  67 /  40  70  70  70  70
Burnet Muni Airport            68  80  66  78  65 /  60  70  60  70  60
Del Rio Intl Airport           72  85  67  82  66 /  60  60  70  60  40
Georgetown Muni Airport        69  81  67  79  66 /  40  70  60  70  60
Hondo Muni Airport             70  83  68  81  66 /  50  70  70  70  50
San Marcos Muni Airport        69  82  67  80  67 /  40  70  70  70  70
La Grange - Fayette Regional   71  83  70  81  68 /  30  70  60  70  70
San Antonio Intl Airport       71  83  68  80  67 /  40  70  70  70  60
Stinson Muni Airport           72  84  69  81  68 /  40  70  70  70  60




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