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Area forecast discussion
National Weather Service Austin/San Antonio Texas
957 am CDT Tue may 23 2017

Update...
latest surface analysis showed the southward progressing cold front
near Abilene with a prefrontal north wind shift evident on surface
obs. Breaks in the cloud cover should allow for adequate surface
heating to lead to cape values this afternoon in the 2000-2500 j/kg
range. Shear values will be strong enough to support some
supercellular structures with the moderately strong instability
values with any afternoon convection. The latest day 1 outlook has
expanded the slight risk to cover a large portion of our eastern and
southern County Warning Area and this looks good. Convection chances should begin to
arrive to our northern zones around the noon hour and will last
through the early evening with rain chances ending from north to
south as drier air filters in behind the front. The main hazard will
be large hail this afternoon and evening but some damaging winds
will be possible, especially for the southern areas. Made some minor
adjustments to the pop grids to configure them based on latest
thinking.

&&

Previous discussion... /issued 656 am CDT Tue may 23 2017/

Aviation.../12z_tafs/
a wide range of ceilings exist across south central Texas this
morning due to multiple boundaries that pushed through overnight
associated with convection north of the region. Although aus is
currently LIFR and ssf is currently skc, MVFR is most prevalent north
of the Highway 90/Interstate 10 corridor including at Sat and drt.
Thus, the taf forecast generally trends all sites towards MVFR within
the next few hours with an IFR tempo group at drt before recovering
them to VFR as the cold front currently along the Interstate 20
corridor approaches and shower and thunderstorm chances increase.

Scattered strong to severe thunderstorms are expected along and
behind the front at the I-35 taf sites. If the complex along the
Interstate 20 corridor holds together and maintains its speed, it
would be at aus by 17z and Sat/ssf shortly thereafter. However,
aircraft soundings still show that the I-35 corridor is pretty
stable. Thus, for now have included general showers after 17z with
tempo thunderstorms and rain between 17-20z at aus and 18-21z at Sat/ssf. For now, have
left out any mention of rain showers or thunderstorms and rain at drt as chances are currently
too low to include in the tafs. Northerly winds may briefly gust to
20-25 knots behind the front before quickly subsiding by evening with
skies rapidly clearing.

Previous discussion... /issued 415 am CDT Tue may 23 2017/

Short term (today through wednesday)...
area radar data shows some convection ongoing across central and
North Texas early this morning. Radar and satellite trends do show a
gradual weakening trend with this convection as it moves eastward
into a more capped environment.

The main forecast concern for today will be the chance for strong to
severe thunderstorms. Given the recent observations and hi-res models,
suspect most of the morning hours should remain fairly quiet as
outflow from morning activity should tend to stabilize the lower
levels. However, given the active northwest flow aloft, we will keep
a chance of showers and thunderstorms in the forecast for most areas
this morning. For this afternoon, the active northwest flow aloft
will help drive a cold front into south central Texas. Low- level
lift along this front combined with an upper trough axis and cold
pool aloft should be enough to generate scattered thunderstorms this
afternoon. Given some decent CAPES (1500-2500 j/kg), 0-6km bulk shear
vectors of 40-50kt and steep mid-level lapse rates, some storms will
be capable of producing large hail and damaging winds. While the
best chance for severe storms should remain generally south of U.S.
Highway 90, we can't rule out a few severe storms across The Hill
Country and I-35 corridor. The chance for severe weather will
decrease by mid- evening as cooler and drier air in the low-levels
moves in behind the cold front. The forecast for Wednesday will
remain quiet as the above mentioned upper trough axis moves east of
the region.

Long term (wednesday night through monday)...
dry weather along with a warming trend can be expected across all of
south central Texas for Thursday through Saturday. Above normal
temperatures are expected with highs in the mid 80s to upper 90s
along with overnight lows in the 70s. The next chance for rainfall
will be late in the forecast period on Sunday and Monday as the flow
aloft becomes increasingly active. A weak cold front may also enhance
rain chances during this time frame. For now, we will keep rain
chances in the 30-40% range across most areas. Temperatures will also
trend downward given the potential for rain and a cold front.

&&

Preliminary point temps/pops...
Austin Camp Mabry 79 57 84 64 91 / 50 30 - 0 0
Austin Bergstrom Intl Airport 79 55 84 61 91 / 50 30 - 0 0
New Braunfels Muni Airport 80 55 84 61 91 / 50 30 - 0 0
Burnet Muni Airport 75 53 83 62 89 / 50 20 - 0 0
del Rio Intl Airport 82 59 86 65 94 / 40 10 - 0 0
Georgetown Muni Airport 77 54 82 62 90 / 50 20 - 0 0
Hondo Muni Airport 82 53 85 61 92 / 40 20 - 0 0
San Marcos Muni Airport 80 54 84 61 91 / 50 30 - 0 0
La Grange - Fayette regional 80 55 83 62 89 / 50 40 - 0 0
San Antonio Intl Airport 80 57 85 63 92 / 50 30 - 0 0
Stinson Muni Airport 79 57 85 62 92 / 50 30 - 0 0

&&

Ewx watches/warnings/advisories...
none.
&&

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