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Area forecast discussion
National Weather Service Austin/San Antonio Texas
629 am CDT Sat may 27 2017

Aviation...
MVFR ceilings and some patchy drizzle continues at the area airports
and should continue to see these restrictions until the early
afternoon hours before VFR returns. Southerly winds will be in the 10
to 15 knot range for the most part. Another round of MVFR stratus is
likely tomorrow night.

&&

Previous discussion... /issued 351 am CDT Sat may 27 2017/

Short term (today through sunday)...
rich low level moisture and favorable isentropic lifting in the
lowest 100 mb early this morning will result in drizzle/mist for the
eastern half of the County Warning Area. Rap moves this lifting area north around 12z
and should reduce the drizzle but many areas will likely wake up to
wet ground this morning.

Moving through the rest of the day, a dry line will set up to the
west again this afternoon. While dewpoints in the 70s, a dry line in
the west, and a continued southerly fetch typically is an Eyebrow
raiser this time of the year for storm development, a Stout cap at
around 800mb doesn't look to budge as evidenced in rap forecast
soundings over Austin, San Antonio, and The Hill Country. Farther
west near del Rio, much weaker capping is forecast but surface
moisture will be a bit less impressive which results in convective
temps of 101+ this afternoon. Looks like the best shot at any storms
for the County Warning Area this afternoon will be if any del burro supercells can
get going. There are some indications this may occur due to an
easterly shift to the low level wind field this afternoon which may
be enough to get convection firing over Mexico. Chances of these
cells crossing the border look slim though. Left slight pops out
there for now. Also, forecast heat indices may reach into the upper
100s this afternoon, but opted against a heat advisory at the moment
as values looked to be just below criteria. Will need to watch this
closely this afternoon.

Later tonight, an approaching cold front will be the focus for
lifting and perhaps some showers and thunderstorms tomorrow morning
as it approaches the northern periphery of the County Warning Area. However, a weak
shortwave disturbance is progged to move across the area Sunday
afternoon and amplify lift over our very moist atmosphere. Ttu-WRF
aggressively convects tomorrow afternoon along a line from Sonora to
Lampasas and then shifts the activity southeast into south central
Texas. With GFS precipitable water 1.7+" tomorrow afternoon across the area and
3000+ j/kg for surface based parcels to tap into as the convection
produces outflow and shifts southeast, should see heavy rainfall
rates and likely a straight line wind and hail threat. We are
currently slight risked for Sunday for 2/3 of the area.

Long term (sunday night through friday)...
a stalled front will be positioned north of the County Warning Area Monday which will
keep south central Texas in the moist regime it's been in. Weak low
level flow out of the east should limit potential for heavy rainfall
Monday beyond the previous night's complex. But having said that,
both the GFS and European model (ecmwf) produce another 1/2 inch to inch of rainfall
over the southern half of the cwa, likely due to an uncapped unstable
atmosphere. If remnant outflow boundaries are present Monday, they
would be the focus for potential heavy rainfall, but for now, have
kept quantitative precipitation forecast values generally conservative due to the unfavorable wind
field being advertised.

The 500 mb pattern agreement begins to diverge beginning mid week as
either weak ridging (gfs) or weak troughing (ecmwf) sets up across
the region. The troughing solution would prove to the rainiest as
continued broad upper level lifting allow for rain chances through
the next weekend. GFS solutions keep the majority of the quantitative precipitation forecast
generation north and west of the cwa, closer to the main shortwave it
advertises set up over The Rockies. As a result, opted to broad brush
at least chance pops or better throughout the remainder of the
extended, hopeful that more clarity will come in the extended with
later runs.

&&

Preliminary point temps/pops...
Austin Camp Mabry 76 90 69 83 68 / 10 40 60 50 30
Austin Bergstrom Intl Airport 75 91 69 82 67 / 10 30 60 50 30
New Braunfels Muni Airport 76 91 70 81 67 / 10 30 60 50 30
Burnet Muni Airport 73 86 66 81 64 / 20 50 60 40 30
del Rio Intl Airport 77 91 71 83 69 / 20 40 60 60 30
Georgetown Muni Airport 75 88 67 81 65 / 20 40 60 40 30
Hondo Muni Airport 76 91 70 83 67 / 10 30 60 60 30
San Marcos Muni Airport 76 91 69 81 67 / 10 30 60 50 30
La Grange - Fayette regional 76 91 71 81 68 / 10 30 60 60 30
San Antonio Intl Airport 76 91 71 82 68 / 10 30 60 50 30
Stinson Muni Airport 76 91 72 82 69 / 10 20 60 60 30

&&

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

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