Area Forecast Discussion
Issued by NWS Austin/San Antonio, TX

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FXUS64 KEWX 181753

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1153 AM CST Tue Dec 18 2018

Visibility has come up and ceilings are beginning to clear along the
I-35 terminals with SAT and SSF already going VFR. Fog and low clouds
are hanging on at AUS and along the Rio Grande at DRT, but clearing
should take place at both those sites over the next 1 to 3 hours with
VFR flying conditions across South Central Texas expected by 21z
this afternoon. Winds today will be light out of the east and

Ceilings and visibility will tank again tonight. MVFR should begin
between 04z to 06z with IFR setting in around 06z/07z. Cigs and visby
will continue to fall to IFR/LIFR levels between 09z and 12z and
will remain Wednesday through most of the morning. While this
pattern is almost a carbon copy of this morning, Wednesday could see
the addition of isolated showers overnight tonight into tomorrow
morning. While these are not mentioned in the TAFs at this point due
to their isolated nature the best chance will be after 06z and
around AUS. Later TAF cycles may need to add the mention of
precipitation to the TAFs.

Wednesday mid day will see the slow improvement in ceilings and
visibility again with any precipitation that was afoot ending by 18z
as VFR conditions return. West and northwest winds will work in
behind the departing trough on Wednesday.


.PREV DISCUSSION... /ISSUED 410 AM CST Tue Dec 18 2018/

SHORT TERM (Today through Wednesday)...
Very low stratus and dense fog are spreading to the northwest across
our area per surface observations and traffic cameras. Weak drainage
flow is keeping the dense fog away from the Escarpment. However,
expect that flow to stop allowing the dense fog to move into those
areas. The dense fog should persist through mid morning. As a result,
have issued a Dense Fog Advisory for areas along and southeast of the
Escarpment through 9 AM CST. Fog will move into the Hill Country and
may become dense. May have to extend the Advisory for those areas
later. The fog should lift by mid morning as lower level flow from
the south increases allowing for some mixing while the stratus lifts.

An upper level trough moving across New Mexico and Chihuahua state of
Mexico will move into Western Texas as the day progresses. Deepening
moisture and increasing upward forcing may lead to isolated showers
across northwestern Val Verde County and near the Coastal Plains this
afternoon. Strongest forcing and deepest moisture with PWs up to 1.2
inches are tonight. Have maintained chances of showers for all areas,
except along Rio Grande where drier air lingers. Have added a slight
chance of thunderstorms across eastern areas due to steep mid level
lapse rates. Lightning products have shown a few lightning strikes as
the system approaches El Paso. A shortwave dropping into Texas from
the northwest, slows the upper trough as it moves away on Wednesday,
keeping slight chances of showers a little further west than earlier
forecast. Regardless, chances end around midday.

LONG TERM (Wednesday Night through Monday)...
As the trough moves further away, the shortwave will rotate through
our area Wednesday night, then both features and a northern stream
trough generate a deep upper level trough that drifts to the east
across the Eastern States. In the wake of these features, a tight
pressure gradient develops and along with mixing of strong winds
aloft (models show 925 MB to 850 MB winds of 40 to 55 KTs), breezy
to windy conditions develop on Thursday. Wind gusts in excess of 40
MPH are possible. A Wind Advisory may be needed for parts of our
area. In addition, a drier airmass filters into our area to create
elevated fire weather conditions. However, weak cold advection
should keep humidities from bottoming out. Ridging at the surface and
aloft move across our area on Friday into Saturday with a warmer
southwesterly lower level flow developing. Models show a cold front
moving across our area this weekend. Have gone with slower frontal
passage as shown by the ECMWF due minimal support aloft for a faster
passage, although suspect it could be delayed even further. A dry
frontal passage is expected due to lack of moisture return. For
Christmas Eve into Christmas Day, there remains a potential for
showers due to upper level impulses moving in the southwestern flow
aloft combined with increasing moisture in a warm advection pattern.
Expect the forecast to fine tune the details of the holiday forecast
as models come into better focus.


Austin Camp Mabry              65  51  67  47  63 /  10  40  20   0   0
Austin Bergstrom Intl Airport  65  51  68  47  63 /  10  40  20   0   0
New Braunfels Muni Airport     64  51  68  47  63 /  10  40  20   0   0
Burnet Muni Airport            64  48  65  43  60 /  10  40  20   0   0
Del Rio Intl Airport           63  46  71  44  67 /  -   10  -    0   0
Georgetown Muni Airport        64  50  64  47  61 /  -   40  20   0   0
Hondo Muni Airport             65  48  72  44  69 /  -   30  10   0   0
San Marcos Muni Airport        65  51  69  47  64 /  10  40  20   0   0
La Grange - Fayette Regional   65  52  67  48  63 /  10  50  20  -    0
San Antonio Intl Airport       64  51  69  48  65 /  10  30  20   0   0
Stinson Muni Airport           64  51  70  48  67 /  10  30  20   0   0


Dense Fog Advisory until noon CST today for Bastrop-Fayette-Lavaca-



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