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December 30, 2014

TK’s Special Briefing….

by troyk | on Dec 30, 2014 | Comments Off

Austin / Travis County and South Central Texas Weather Statement #2
Prepared by UT University/Incident Meteorologist Troy Kimmel
1110am CT – Tuesday / 30 December 2014

.. Colder Arctic Air and Precipitation Chances for the New Years Eve and New Years Day Period ..
.. NWS Issues Winter Storm Watch for Texas Hill Country ..

NWS WATCHES / ADVISORIES / WARNINGS:
NWS /  Winter Storm Watch (Valid 6pm Wed/31Dec2014 until 12noon Thu/01Jan2014)
Counties Included.. Blanco.. Burnet and counties westward through the hill country
Ice accumulations to 1/10th inch or slightly more possible.

SYNOPTIC/FORECAST REASONING:
A large center of arctic high pressure.. currently centered over Montana with a surface pressure
of 1053mb.. continues to slide south southeastward along and to the east of the Rockies into the plains states
on this Tuesday morning with the coldest air will settling over our area by late tonight into New Years Eve
and New Years Day. By tomorrow evening, the enter of the high pressure, 1036mb surface pressure, is
forecast to be over Oklahoma and Arkansas.

On this Tuesday morning, we’re seeing some patchy light rain and drizzle along with patchy fog over the area
with temperatures in the low and middle 40s.

As the day goes along, arctic air will continue to move in at the surface. At mid and late morning, single digit
temperatures have spread as far south as Amarillo where it is 9 degrees F. By late tonight into Wednesday
morning and continuing through New Years Day, as the much colder arctic surface air – forecast only a few
thousand feet thick – is overrun by moisture and by passing upper air low pressure disturbances, light
overrunning precipitation will develop over the area. Surface air temperature is going to be the key factor on
whether we simply see a cold rain/drizzle or whether we could see the possibility of freezing rain and freezing
drizzle. Based on forecast atmospheric soundings, sleet/ice pellets may be a factor in areas further northwest
of Austin while, at this point, snow should not be a factor based on the forecast of very shallow surface based
cold air.

At this point, my confidence of any freezing precipitation has increased slightly especially in areas along and
west of the IH35 corridor.  Although I’ve slightly expanded the time periods, I still believe that the main times
of concern around the south central Texas area are in a window 3am to 10am tomorrow morning and again from
5pm Wednesday through 12 noon on Thursday /New Years Day/. Although the main risk area is expected to
remain to the northwest of the Austin metro area/IH corridor, but it could be too close for comfort. Needless to
say, all areas from the Austin metro area/IH35 corridor counties of Williamson, Travis and Hays counties
westward through the hill country should remain alert to the latest watch/advisory/warning issuances from the
National Weather Service Austin-San Antonio.

The main part of the upper air low pressure disturbance will cross the area by late Thursday night into Friday
night with the best chance of rain and even a few thunderstorms across our area. It would appear that surface
temperatures will have warmed a few degrees by then with temperatures well above critical freezing levels.
A reminder that models, however, have a tendency to dislodge colder based surface air too quickly so let’s
watch this closely.

With the passage of the upper air low pressure disturbance, rain chances will end locally with clouds
breaking/clearing by midday into early afternoon Saturday.

THREAT(S):
Low to moderate probability – Freezing drizzle / freezing rain (some sleet/ice pellets northern hill country)
Geographic area: Western third of Travis, Williamson and Hays counties westward over the hill country
Time Period: Possible in the 3am to 10am Wednesday (31 Dec) time period
Time Period: Possible in the 5pm Wednesday (31 Dec) through 12 noon Thursday (1 Jan 2015) time period.

MY FORECAST CONFIDENCE:
Weather system evolution: High to very high
Precipitation chances: Very high
Liquid precipitation (rain) chances: Very high
Freezing precipitation (freezing rain/freezing drizzle) chances: Low to moderate
Frozen precipitation (snow/ice pellets-sleet) chances: Very low
Thunderstorm/lightning chances: High to Very High
Severe thunderstorm chances: None

AVIATION INFORMATION FOR THE AUSTIN/BERGSTROM
INTERNATIONAL AIRPORT (KAUS) AERODROME:

Any freezing precipitation occurring at ABIA would have impacts and all airport
interests should closely monitor this situation over the next 24 to 36 hours.

. Current KAUS Terminal Aerodrome Forecast (TAF) – Issued 301600z ..

KAUS 301600Z 3016/3118 03010KT 1SM BR OVC002
     FM301800 02015KT P6SM BKN015==

. For Our DAL/DFW Hub Aerodromes ..
Current NWS public forecasts have introduced a rain and ice pellet/sleet mix
for the Dallas/Fort Worth area for Wednesday night… precipitation probability 20%.

. For Our HOU/IAH Hub Aerodromes ..
Current NWS public forecasts do not have any freezing or frozen precipitation
for the New Years Eve/New Years Day forecast period. Isolated thunderstorms
are mentioned for Thursday night.. Friday.. Friday night and early Saturday.

Current FAA National Airspace Status

CALL TO ACTION:

Please remain “weather aware” and listen for the latest weather statements,
advisories, watches and warnings from the National Weather Service.

Make sure that your NOAA All Hazards Weather Radio is operational and are
set to alarm in case of severe and inclement weather watches and/or warnings.

FOLLOWUP STATEMENTS:

I will continue to keep you informed regarding this severe/inclement weather
event. Any questions, please let me know at tkimmel@austin.utexas.edu

GENERAL WEATHER INFORMATION LINKS:

NWS/Austin-San Antonio Current Statements/Advisory/Watches/Warnings
NWS/Austin-San Antonio Web Page
NWS/Storm Prediction Center (Outlooks)
NWS/Storm Prediction Center (Mesoscale Discussions – Severe Weather & Snow)
NWS/Storm Prediction Center (Severe Thunderstorm/Tornado Watches)
NWS/Weather Prediction Center (Mesoscale Discussions – Heavy Rain & Flooding)
NWS/National Hurricane Center

tk