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National Weather Service Austin/San Antonio TX
431 PM CDT SAT SEP 24 2016

.SHORT TERM (Tonight through Sunday Night)...
A deep mid-to-upper level trough currently moving into the Rocky
Mountains is helping stream deep tropical moisture ahead of it
from west Texas into the Central Plains. A cold front currently
extends from an occluding low pressure system in North Dakota
through the central Plains into the Texas-Oklahoma panhandle, from
which a stationary front extends down through west Texas. Ahead of
this system in South Central Texas, isolated to scattered showers
and thunderstorms are ongoing along and east of Highway 281 as an
additional surge of Gulf moisture interacts with weak outflows
and 2000-4000 J/kg of CAPE. Brief heavy downpours and wind gusts
to 40 miles per hour due to DCAPE values near 1000 J/kg will be
the primary threats with these storms as rainfall totals generally
remain below half an inch. In addition, gusty S-SE winds up to 25
miles per hour are occurring across the region this afternoon
ahead of this frontal system. Convective coverage will be a little
greater for the eastern half of the CWA tomorrow afternoon with
the heavy rainfall threat remaining to the west.

Isolated showers and thunderstorms are possible tonight across
the entire region, but the best chances for more scattered to
widespread showers and thunderstorms will be in the Edwards
Plateau and northern Rio Grande Plains. Scattered showers and
thunderstorms currently forming over the mountains in Coahuila
will affect western Val Verde County late this afternoon and
early evening as they dissipate to produce up to 1-2 inches of
rain. Hi-res and global models display considerable uncertainty
for these areas later this evening and overnight as showers and
thunderstorms currently forming along a weak pre-frontal trough
or confluence zone in west Texas and Big Bend will gradually slide
southeast tonight. This will occur as a piece of energy splits off
of the trough to our west over the southern parts of AZ and NM,
potentially ejecting a weak shortwave to the northeast. If the
shortwave comes to fruition, storms may slip into the western
Hill Country towards the I-35 corridor by sunrise as a few hi-res
models suggest. Otherwise, most models depict a less progressive
solution keeping rainfall north and west of Val Verde and Edwards
Counties with some hi-res models and the EURO depicting some
heavier rainfall for Val Verde County between 6-12Z while most
hold off until after 12Z. However, locally heavy rainfall will be
possible over this area if the system becomes more progressive
given a southerly 30 knot LLJ that will help focus convection.

Most models depict the cut off low to our west will very slowly
retrograde to the southwest on Sunday as convection gradually
propagates south and east. Confidence continues to increase that
locally heavy rainfall capable of producing flash flooding will
occur along and west of the Highway 83 corridor. However, rainfall
amounts have increased slightly and the timing of this rainfall
has moved up to early tomorrow afternoon into the early morning
hours on Monday as models continue to trend towards a bit more
progressive solution. Convective coverage should increase early
tomorrow afternoon west of Highway 83 as increasing instability
with daytime surface heating interacts with PVA aloft, isentropic
ascent with the front approaching from the northwest, a southeast
LLJ, and deep moisture. This convection will continue to
propagate east into the I-35 corridor overnight Sunday into Monday
as the front moves through the region, but rain amounts should be
lower given lower dynamic forcing aloft from the retrograding low.

Rainfall amounts of 3-6 inches with isolated totals exceeding 8
inches will be possible for this event through Monday along and
west of Highway 83. Similar rainfall amounts across the border
into Mexico will also accentuate flooding issues for communities
along the Rio Grande like Del Rio and Eagle Pass. Rainfall amounts
of 1-3 inches are expected for areas between Highway 83 and the
I-35 corridor, while rain amounts east of I-35 should remain below
1 inch on average with some locally heavier amounts. If confidence
continues to increase for the timing and rain amounts with this
system, a Flash Flood Watch may be issued for the western counties.


.LONG TERM (Monday through Saturday)...
Scattered showers and thunderstorms will continue behind the cold
front on Monday across most of the region as isentropic ascent
occurs aloft behind the surface front. However, any locally heavy
rainfall threat that would exist (but be less likely as the upper
level low retrogrades further west) should remain confined to the
Rio Grande Plains. Given northerly winds, cloudy skies, and
strong cold air advection, temperatures on Monday and Tuesday will
struggle to get out of the 70s across most of the region.
Nighttimelows will dip into the mid 50s to mid 60s, but may fall
further Tuesday night into Wednesday if any significant clearing
is able to occur. A progressive upper level ridge will begin to
move over the region by Wednesday and continue through the end of
next week to allow temperatures to warm back up into the mid 80s
with mostly clear skies and dry weather.


Austin Camp Mabry              75  90  69  80  63 /  30  50  70  50  30 
Austin Bergstrom Intl Airport  74  90  69  81  63 /  30  50  70  50  30 
New Braunfels Muni Airport     74  90  69  82  63 /  30  50  70  60  40 
Burnet Muni Airport            73  86  65  75  60 /  40  60  80  50  30 
Del Rio Intl Airport           75  84  68  76  61 /  60  80  90  70  60 
Georgetown Muni Airport        74  88  66  77  62 /  30  60  80  50  30 
Hondo Muni Airport             76  90  69  82  63 /  30  50  80  60  50 
San Marcos Muni Airport        74  89  68  80  63 /  30  50  70  60  40 
La Grange - Fayette Regional   75  90  70  84  67 /  20  50  60  50  30 
San Antonio Intl Airport       76  90  70  81  64 /  30  50  70  60  40 
Stinson Muni Airport           77  90  71  83  66 /  30  50  70  60  40 




Public Service/Data Collection...Williams

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