Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Austin/San Antonio Texas
1129 PM CST Wednesday Dec 4 2013
no significant changes to ongoing tafs. South to southeasterly
flow will continue overnight bringing warm...moist air into the
region. Beginning to see visible dropping in fog. Expect this trend to
continue and also looking for ceilings to drop. Expecting flying
conditions to drop to IFR by around 07z and to vlifr a couple of
hours later. Should see some improvement near sunrise when a cold
front will move through and turn the winds around to the north.
Then ceilings will rise to MVFR late morning Thursday. Winds will be
out of the north at 15 with gusts to 25 kts during the day
Thursday. Expect slight chance for rain after 00z which should be
light and have little impact on visible. Better chance for rain after
06z at 30 hour airports.
Previous discussion... /issued 1005 PM CST Wednesday Dec 4 2013/
we have updated the forecast to include a dense fog advisory for
areas generally along and east of the I-35 corridor.
dew points in the upper 50s to upper 60s along with light winds
have allowed fog to develop late this evening. With continued
cooling and light winds...suspect we could see some areas of dense
fog after midnight across portions of south central Texas. The
latest hi-res RUC continues to support the above and we have opted
to issue a dense fog advisory for counties along and east of a
Carrizo Springs to Uvalde to San Antonio to Austin line.
Visibilities of one quarter mile or less possible in the advisory
The latest few runs of the hi-res RUC also continues to show a
quicker frontal passage early tomorrow morning. We have adjusted
the forecast to account for a little earlier arrival of the cold
front. Visibilities will quickly improve behind the front.
Previous discussion... /issued 327 PM CST Wednesday Dec 4 2013/
Short term (tonight through Thursday night)...
above normal temperatures will continue this evening with low
clouds and patchy fog developing late tonight. The strong Arctic
front is set to enter the forecast area by around 09z and into
Austin by 12z and Sat by 15z. Model run-to-run trends suggest a
slight acceleration of the front possible. Daytime temperature
trends continue downward for Thursday...and by late evening...a few
locations of the northern Hill Country may be at risk of
reaching the freezing mark. Similar to the previous Arctic
front... light to moderate rain showers are expected to overrun
the Arctic air and produce a threat of freezing rain...especially
late Thursday night. Pf amounts will be mainly below 1/10 inch...
and so a Winter Storm Watch is not anticipated at this time. A
Winter Weather Advisory level threat is currently anticipated...
with warm ground temperatures expected to confine early icing to
mainly bridges and overpasses.
Long term (friday through wednesday)...
precipitation rates are expected to decrease Friday as a shallow
shortwave trough passes mainly north of the area. Isentropic lift
over the front is expected to continue through the weekend...but
will have to overcome continued dry air reinforcement in the
lowest 3000 feet or more. Light rain and sprinkles will eventually
be reduced to drizzle at the surface...so very little icing is
anticipated...despite several hours of opportunity of freezing
drizzle and sleet shown in the forecast. Persistent evaporative
cooling from the light precipitation pattern and model trends on
temperatures suggest this air mass will be colder than the one
prior to Thanksgiving. If any shortwave activity is detected in
the broad zonal flow aloft...the higher precipitation rates that
result would warrant a Winter Storm Watch or warning to be
By late Sunday morning...a more significant shortwaves in
the flow aloft is expected to pass north of south central Texas.
As it does so...there is a good chance for wake subsidence to
clear out skies and modify the temperatures to end the freezing
precipitation potential. Model trends...especially from the
GFS...show the base of the broader upper trough becoming more
shallow Sunday into Monday...thus further increasing the chance
for clearing skies. Nevertheless...cold air advection will be
further reinforced on Monday with the coldest morning lows of the
season expected over many areas by Tuesday morning. A split flow
pattern remains in the forecast for the rest of next week...
leading to a higher chance for cloud cover and cooler than
normal temperatures continuing into next weekend.
Preliminary point temps/pops...
Austin Camp Mabry 51 57 33 38 29 / 10 30 70 60 20
Austin Bergstrom international Airport 54 59 34 38 28 / 10 30 70 60 20
New Braunfels Muni Airport 60 62 37 39 29 / 10 30 70 50 30
Burnet Muni Airport 46 49 31 35 25 / 10 30 70 50 20
del Rio International Airport 60 68 39 47 33 / - 20 60 20 -
Georgetown Muni Airport 48 53 31 35 26 / 10 30 70 60 20
Hondo Muni Airport 60 67 38 40 33 / 10 20 60 30 20
San Marcos Muni Airport 59 61 36 38 29 / 10 30 70 60 20
La Grange - Fayette regional 65 67 38 39 33 / 10 30 60 70 30
San Antonio International Airport 62 64 36 39 32 / 10 20 70 50 20
Stinson Muni Airport 63 65 38 41 34 / 10 20 60 50 20
dense fog advisory until 6 am CST Thursday for the following
counties: Atascosa...Bastrop...Bexar...Caldwell...Comal...De Witt...