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Area forecast discussion
National Weather Service Austin/San Antonio Texas
607 PM CST Wed Jan 18 2017

Aviation...
IFR/low end MVFR cigs this evening over The Hill Country to across
the I-35 corridor northeast of ksat into southeastern Texas will
lower to LIFR overnight into Thursday morning. As downslope flow
ends, cigs will redevelop and lower across areas along and south of
the Highway 90 Escarpment east to ksat to west of I-37 due to the
downslope flow, becoming LIFR overnight. Br with IFR/MVFR vsbys will
develop overnight into morning with possible vlifr/LIFR where the
soils are more saturated due to recent rains. Have kept these lower
vsbys out of the taf sites for now as low stratus may inhibit the
lower vsbys. Will monitor observational and model trends for later
mention. Lower level flow increases late morning with skies mixing
out to VFR midday into the afternoon. The upper level trough moves
across our area early Thursday generating scattered rain showers/isolated thunderstorms and rain east of
I-35 overnight into morning with no impacts to taf sites. Variable winds
5 kts or less tonight will become SW to west 5 to 12 kts on Thursday.

&&

Previous discussion... /issued 342 PM CST Wed Jan 18 2017/

Short term (tonight through Thursday night)...
showers and thunderstorms have pushed east of the region as
isentropic descent has settled in over the region behind this
morning's shortwave. Skies are beginning to clear across parts of the
Rio Grande plains from just south of del Rio to the I-35 corridor as
far north as San Antonio. This has allowed temperatures over those
areas to warm rather quickly up into the mid to upper 60s above
forecast highs whereas elsewhere low clouds should persist through
the rest of the afternoon to keep highs in the mid 50s to lower 60s.

Dew points tonight should remain in the upper 40s to lower 50s as
temperatures cool to their dew points which combined with weak winds
and clearing skies along and west of I-35 should allow for at least
patchy fog to develop after 12-2 am. There should be enough clouds
and shower activity east of the I-35 corridor to prevent fog from
developing in those areas as one final shortwave rotates around the
upper level low centered over SW Kansas and southeast Colorado to cause another brief
period of isentropic ascent after midnight over our southernmost
counties and the coastal plains. Light to moderate rain showers with
perhaps an isolated thunderstorm will occur over those regions
through mid-morning before any rainfall, cloud cover, and fog quickly
exits the region. Southwest winds at 5-10 mph under clear skies with
850 mb temps around 10 deg c should allow for effective mixing to get
highs generally in the mid 70s tomorrow.

Long term (friday through wednesday)...
dry weather is generally expected over the next seven days aside from
possibly some very isolated showers and thunderstorms east of the
I-35 corridor on Friday afternoon and evening and north of I-10 on
Saturday. Hi-res models and the NAM are not very bullish on rain
chances for Friday given some drier air aloft and weak isentropic
ascent, but have maintained 20 pops due to shortwave forcing moving
through the region. Rain chances for Saturday are trickier as a cold
front moves through the region but we generally remain on the west
side of the shortwave with negative vorticity advection aloft. For
now, have maintained 20 pops north of the I-10 corridor, but have
moved rain chances out of the region by early Saturday evening as dry
air should quickly filter in behind the front. Future model cycles
should better resolve the timing of the shortwave with the frontal
forcing that will either cause pops to be removed or increased.

The biggest weather story of the upcoming week continues to be windy
conditions on Sunday as the upper level disturbance responsible for
saturday's front continues to deepen and dig southeast from Oklahoma
into the lower Mississippi Valley. Northwest 50-60 knot winds are
forecast by the GFS at 925 mb over our southern counties by Sunday
morning before subsiding by the afternoon hours below 40 knots.
Sustained winds out of the northwest at 20-30 mph gusting in excess
of 40 mph are expected after midnight on Sunday and should extend
into the afternoon as the surface pressure gradient strengthens in
response to the deepening upper low to our northeast. However, if
the timing of the strongest winds at 925 mb and strengthening
pressure gradient are both delayed a few hours, we could have gusts
much greater than 40 mph as they would occur later in the morning
closer to peak heating with more effective mixing of the stronger
winds down towards the surface. Regardless, we expect a very windy
Sunday morning and afternoon with elevated to near critical fire
weather conditions over most of the region with relative humidity
values generally in the 20-30 percent range. Temperatures recover
quickly behind the front for Monday and Tuesday to allow for a few
more days of above normal temperatures before yet another dry front
passes through the region Tuesday afternoon and evening to possibly
begin a prolonged period of cooler than normal temperatures.

&&

Preliminary point temps/pops...
Austin Camp Mabry 50 75 51 78 55 / 10 10 0 10 10
Austin Bergstrom Intl Airport 49 75 50 77 55 / 10 10 0 10 10
New Braunfels Muni Airport 50 74 51 76 55 / 10 10 0 10 10
Burnet Muni Airport 45 73 47 74 50 / 10 10 0 10 10
del Rio Intl Airport 45 75 45 76 51 / - - 0 - -
Georgetown Muni Airport 47 74 48 76 53 / 10 10 0 10 10
Hondo Muni Airport 48 75 48 78 51 / 10 10 0 10 -
San Marcos Muni Airport 50 74 51 76 55 / 10 10 0 10 10
La Grange - Fayette regional 52 73 55 75 58 / 40 20 - 20 20
San Antonio Intl Airport 51 75 52 77 55 / 10 10 0 10 10
Stinson Muni Airport 52 75 51 77 55 / 10 10 0 10 10

&&

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

$$

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