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

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452
FXUS64 KEWX 180001 AAA
AFDEWX

Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
601 PM CST Wed Jan 17 2018

.AVIATION.../00Z TAF CYCLE/

VFR conditions to prevail through the TAF period as OVC060
altostratus deck shifts north through the next 6 hours. KAUS will be
under the deck near 03-04Z with all other sites already under the
mid-level clouds. Cloud ceilings will slowly lower through Thursday
but remain VFR. Surface winds will be light and variable overnight
and then switch to the east and southeast Thursday afternoon while
remaining below 10 knots.

&&

.PREV DISCUSSION... /ISSUED 241 PM CST Wed Jan 17 2018/

SHORT TERM (Tonight through Thursday Night)...
The focus of the short term period was on tonight`s potential hard
freeze and prospects for any wintry precipitation associated with an
approaching upper low.

Over the course of the day, a stubborn cloud shield has been observed
across the southwest 2/3 of the CWA which prevented low temperatures
from plummeting much like locations in our northern CWA this morning.
This cloud shield, despite some model guidance indicating otherwise,
has not shown any signs of dissipating. As this upper low continues
to approach, GFS moisture fields bring in high clouds to boot in this
area. As a result, temperature guidance along the Rio Grande Plains
is probably too cold again tonight and likely won`t get as cold as
locations in the Austin area and Hill Country, where only slightly
higher lows from yesterday are forecast.

Additionally, some upper level energy is progged to wrap around the
low overnight and could produce some elevated precip over the Big
Bend and Rio Grande Plains. Interrogation of forecast soundings do
show a weak warm nose (+1C) just below 700 mb but due to dry air
below that layer, will likely be able to dry-bulb down to below
freezing, especially if hydrometeors are seeded above 500 mb. But, if
surface temperatures aren`t able to even reach freezing, then the end
result at the surface may end up being some very light rain and
snowflakes. Hi-res guidance has been inconsistent on resolving precip
development overnight, and synoptic models bring in this precip later
in the day, when most locations are above freezing. Either way, the
very dry low level atmosphere should prevent anything in the way of
significant QPF and thus no impacts are expected.

The low is expected to begin to push eastward from the Big Bend
region Thursday, tapping into low level moisture farther southeast
late Thursday and producing light shower activity into the overnight
hours. With mostly cloudy skies and warmer temperatures, feel pretty
confident this should all be rain in the southeast, although
temperatures will likely fall into the mid to upper 30s.

LONG TERM (Friday through Wednesday)...
A warm weekend looks to be in store as ridging takes place over the
state after the aforementioned low pushes east. Model guidance is
showing highs in the 70s for both Saturday and Sunday and especially
Saturday, that looks certainly valid.

Maintained southerly low level flow should allow for moisture to feed
into the eastern third of the state over the weekend as well which
will be key in the development for more showers and possibly even
thunderstorms Sunday afternoon as another low and associated Pacific
front push east through the CWA. An impressive LLJ, good lifting
along the front, and shear appears to be in phase along and east of
the I-35 corridor (according to the GFS) Sunday afternoon. Thus,
included isolated thunder mention in the Wx grid for now, but
greatest uncertainty isnt so much thunder potential but timing as the
GFS seems to be quite fast in translation of the front which is often
overdone at the mid-range. So for now, included PoPs across eastern
2/3 of the CWA to account for uncertainty with the higher chance PoPs
across the easternmost areas.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              22  45  35  52  46 /   0   0  10  20  10
Austin Bergstrom Intl Airport  20  44  33  51  45 /   0  -   10  20  20
New Braunfels Muni Airport     24  43  34  52  43 /   0  10  20  30  10
Burnet Muni Airport            19  44  32  53  43 /   0   0   0  10  10
Del Rio Intl Airport           30  47  31  59  39 /  20  20   0   0   0
Georgetown Muni Airport        18  44  32  51  45 /   0   0  -   10  10
Hondo Muni Airport             28  45  36  55  40 /  -   10  20  20  -
San Marcos Muni Airport        22  42  34  51  44 /   0  -   20  30  10
La Grange - Fayette Regional   21  42  34  52  46 /   0  -   20  30  30
San Antonio Intl Airport       26  43  36  52  44 /   0  10  20  20  10
Stinson Muni Airport           26  43  36  53  43 /   0  10  20  20  10

&&

.EWX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

Mesoscale/Aviation...Allen
Synoptic/Grids...05
Public Service/Data Collection...YB



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