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

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FXUS64 KEWX 010101
AFDEWX

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

.UPDATE...
Rain has nearly all moved off to the east with only a few showers
developing west of San Antonio. The atmosphere is fairly worked
over and we think the chances for any more rain this evening are
lower than we previously expected. Have lowered the POPs for the
rest of the evening. Temperatures across the eastern half of the
area are rain cooled and with the sun almost down can`t see any
recovery. So, have also lowered the low temperatures. Still
expecting precip to develop overnight with locally heavy rain
possible.

&&

.PREV DISCUSSION... /ISSUED 653 PM CDT TUE MAY 31 2016/

AVIATION...
This TAF period is a tricky one with ongoing high chances for
convection in the next 24 hours. Showers and thunderstorms should
be over in Austin and San Antonio for the rest of the evening and
VFR conditions should prevail. There is a weakening area of
showers in Mexico that may move across the river, but at this time
that does not look likely. So, DRT should remain VFR through the
evening. In Austin and San Antonio, CIGs will drop to MVFR and
then IFR overnight. Have included TSRA after 06Z or 07Z until
mid-morning Wednesday. This is likely too long a period of rain,
but can`t pin down exact timing right now. CIGs should improve
starting late morning reaching VFR by early afternoon. Convection
is possible during the day Wednesday, but have not included any in
TAFs.

AT DRT CIGs will drop to MVFR around 10z and chances for
convection will begin at that time. CIGs will improve to VFR by
around 15Z.

PREV DISCUSSION... /ISSUED 328 PM CDT TUE MAY 31 2016/

SHORT TERM (Tonight through Wednesday Night)...
The first of many heavy rain episodes and storm complexes is
currently passing through the CWA. The evolution of this system,
which is a combination of high instability, high PWAT, mesoscale
boundary interactions, and upper level shortwave disturbances will
be indicative of the next few days.

Hi-resolution models have been essentially guessing at how to
handle convective initiation and coverage over the last several
days...and with the exception of a decent HRRR handling of today`s
activity, have not improved. Thus, basically the forecast has
heavily favored the synoptic models in conjunction with
collaboration with neighbors and regional offices.

Looking west of the current convection...IR satellite is showing
convection enhancing across New Mexico and south of the Big Bend
region. Believe this area will be round number 2 of heavy rain
potential overnight tonight. While this round will not have the
benefit of the higher instability from this afternoon, and a
somewhat worked over atmosphere, would expect this activity out
west to evolve into a mature MCS and move east into at least the
western half of the CWA late tonight into tomorrow morning.

There may be a lull in activity between the Wednesday morning
activity but it will likely only be brief as the atmosphere
destabilizes again into the afternoon and yet another shortwave
swings northeast across...again...the Big Bend and Edwards
Plateau.

It is extremely difficult to hone in on specific amounts
in any particular region, but given the antecedent conditions that
have been well advertised, the flash flooding risk will be
significant between now and Wednesday night.

LONG TERM (Thursday through Tuesday)...
The heavy rain and flooding threats continue Thursday as the main
upper low responsible for all of these shortwave disturbances
enters the state. By Thursday morning, focused upper level lift
associated with the right entrance region of the upper low will be
positioned from Del Rio to Waco. This, coupled with the same
moisture and instability considerations to today and Wednesday
will likely be our most significant heavy rainfall threat.

At the surface, the EURO and GFS both indicate the development of
a surface low over West Texas and pushes southeast along the Rio
Grande River. This will...yet again...provide a surface based
focus to additional heavy rain development Thursday afternoon and
as the main upper low begins to slow in its movement and becomes
more stagnant, could potentially result in training heavy rainfall
as well. This round could persist through Friday morning before
the heavy rain potential begins to finally wane Friday
evening...if the upper low does indeed move east as progged.

As a result...QPF values have further increased, now expected the
potential for 4-7 inches between now and Friday morning but with
the potential for some areas to reach as high as 15 inches before
this event is over with. If this estimate comes to fruition, flash
flooding impacts will be severe. And with so much uncertainty in
the positioning of certain variables, it is not possible to
highlight any one particular area for this threat. So all persons
in South Central Texas should prepare for the prospect of flash
flooding, perhaps extreme flash flooding, and make plans to be
potentially impacted.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              68  82  69  80  66 /  70  80  80  70  60
Austin Bergstrom Intl Airport  68  82  68  80  66 /  70  80  80  70  70
New Braunfels Muni Airport     68  82  68  80  66 /  70  70  80  70  70
Burnet Muni Airport            67  79  66  78  64 /  70  80  80  70  60
Del Rio Intl Airport           71  86  69  84  66 /  70  80  80  60  40
Georgetown Muni Airport        67  80  67  79  64 /  70  80  80  70  60
Hondo Muni Airport             70  84  68  82  65 /  70  70  80  70  60
San Marcos Muni Airport        70  82  68  79  65 /  70  80  80  70  70
La Grange - Fayette Regional   68  82  70  80  68 /  60  70  80  80  70
San Antonio Intl Airport       70  82  69  81  67 /  70  70  80  70  60
Stinson Muni Airport           71  83  70  82  68 /  70  70  80  70  60

&&

.EWX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Thursday morning for the following
counties: Atascosa...Bandera...Bastrop...Bexar...Blanco...Burnet...
Caldwell...Comal...De Witt...Dimmit...Edwards...Fayette...Frio...
Gillespie...Gonzales...Guadalupe...Hays...Karnes...Kendall...Kerr...
Kinney...Lavaca...Lee...Llano...Maverick...Medina...Real...Travis...
Uvalde...Val Verde...Williamson...Wilson...Zavala.

&&

$$

Mesoscale/Aviation...Allen
Synoptic/Grids...05
Public Service/Data Collection...33


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