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Area forecast discussion
National Weather Service Austin/San Antonio Texas
842 PM CST Sat Dec 16 2017

upper level trough has sped up as it moves across Texas this evening.
Currently, all rain has moved east of Highway 281 at around 20 mph.
Expect all rain to move east of our area by midnight and have trended
pops for this. The surface low southeast of our area will continue to
move away from our area taking the threat for thunder with it. Have
removed thunder from our forecast. Temperatures appear to have
bottomed out and expect them to remain nearly steady overnight as
little or no drop in dewpoints with low clouds and fog expected.
Remainder of south central Texas forecast is on track. Another round
of rain is expected Monday into Tuesday, as well as Thursday night
into next weekend. Models continue to show uncertainty with respect
to winter type precipitation.


Previous discussion... /issued 607 PM CST Sat Dec 16 2017/

Aviation.../00z tafs/

Near steady moderate to heavy rain will impact the Sat/ssf tafs over
the next hour and the aus taf over the next 2 hours. Rain has cleared
well east of drt and patchy fog and IFR cigs are already closing in
as indicated by observations to the south and east. Isolated
thunderstorms will be possible along I-35 in the next 3 hours or so,
but with no indication of discrete storm cells thus far, will keep
this out of the forecast for now. Rains should clear the I-35 taf
sites later this evening with IFR cigs and patchy fog expected to
form readily. No vlifr conditions are in the forecasts, but LIFR
conditions forecast around daybreak are a suggestion that some dense
fog conditions could arise at any of the taf sites. Cigs should
slowly improve during the day, but not all areas are expected to
return to VFR in the afternoon. An upstream disturbance is expected
to reinforce a low cloud presence with an east to southeast surface wind and
swly flow aloft.

Previous discussion... /issued 251 PM CST Sat Dec 16 2017/

Short term (tonight through Sunday night)...
water vapor satellite images show an upper level low pressure system
moving over West Texas and to the northeast. All hires and medium-
range models agreed on continuing to bring this system to the
northeast and into the Southern Plains this evening as it opens into
an upper level short-wave. As the upper level system moves to the
northeast for the rest of this afternoon and evening, light to
moderate rain is expected across the eastern two-thirds of south
central Texas. There will be a window late this afternoon and early
evening for isolated thunderstorms mainly along and east of
Interstate 35 as an upper level wind speed maxima moves across the
area. Also, it could enhance any activity for the period and result
in periods of heavy rain.

Overall, rainfall amounts should stay in the half to one inch range
especially along and east of i35 with the potential for up to two
inches of rainfall along and east of Highway 77.

The rain chances come to an end from west to east this evening with
rain-free weather over all areas overnight tonight. Due to a warm
night and wet surfaces, expect patchy fog to develop late tonight
across much of south central Texas.

Sunday should be dry with clouds lingering all day across the eastern
counties and highs in the 60s.

Long term (monday through saturday)...
another upper level low pressure system is forecast to slowly move
across The Four Corners region on Monday and brings showers and
thunderstorms across the area for the first part of next week. A cold
front passage will enhance the chances for rain on Tuesday. The cold
front and upper level energy will move to the east and southeast
with dry weather expect for Wednesday and Thursday.

Yet, another upper level disturbance and a much strong cold front is
expected on Friday. A cold airmass will spread across the area for
next weekend with lows in the 30s and highs only in the 40s.

There is still a lot of uncertainty for the extended forecast period
as far as the type of precipitation we will get if moisture is
around. We will be closely monitoring model guidance and adjusting
the forecast as you plan for the Christmas Holiday weekend.


Preliminary point temps/pops...
Austin Camp Mabry 43 65 52 64 57 / 100 0 10 30 50
Austin Bergstrom Intl Airport 43 64 51 64 58 / 100 0 10 30 50
New Braunfels Muni Airport 43 64 52 66 59 / 90 0 10 30 50
Burnet Muni Airport 41 64 48 62 55 / 80 0 - 30 40
del Rio Intl Airport 43 59 47 64 53 / - 0 - 10 30
Georgetown Muni Airport 43 64 49 62 55 / 100 0 10 30 50
Hondo Muni Airport 45 62 51 65 58 / 40 0 10 30 40
San Marcos Muni Airport 43 64 51 65 59 / 100 0 10 30 50
La Grange - Fayette regional 44 65 53 67 61 / 100 0 20 40 50
San Antonio Intl Airport 44 64 53 66 60 / 80 0 10 30 40
Stinson Muni Airport 44 63 54 66 60 / 80 0 20 30 40


Ewx watches/warnings/advisories...

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