Austin / Travis County and South Central Texas Weather Update #2
Prepared by UT University/Incident Meteorologist Troy Kimmel
820am CT – Thursday / 16 April 2015

A “Slight” Severe Thunderstorm Risk This Afternoon Through Tonight ..
A “Slight” to “Enhanced” Severe Thunderstorm Risk Tomorrow ..

NWS WATCHES / ADVISORIES / WARNINGS:
At this time, there are no watches/advisories/warnings that include the greater
Austin metro area or the IH35 corridor counties of Travis.. Hays and Williamson.

At the very least, I expect the NWS/Storm Prediction Center to issue severe
weather watch(es) that may cover parts of or the entire area later this afternoon
through tonight and into Friday. In addition, at least, I expect
NWS/Austin-San Antonio to issue Significant Weather Advisories (SPSEWX),
Airport Weather Warnings for Austin  Bergstrom International Airport (AWWAUS)
as well as the possibility of Urban and Small Stream Flood Advisories (FLSEWX).
This would be in addition to other possible short fused convective/flood warnings
that may be required.

SYNOPTIC/FORECAST REASONING:
On the surface weather maps, a surface cold front extends southward from
Nebraska and western Kansas into a surface low pressure area is over the
northwestern Texas panhandle with a cold front extending south southwesterly
through New Mexico. In the upper part of the atmosphere, a strong upper air
low pressure disturbance is located over southeast Utah and the four corners
region.

A south southeasterly surface wind flow continues over our area of Texas. The
upper air low pressure area.. over the four corners region.. advances slowly
east northeastward, this moist flow will continue and actually intensify over next
24 hours.

Meanwhile, atmospheric lift will increase by midday into afternoon today with
scattered rain showers and thunderstorms developing and becoming more numerous
late this afternoon into tonight and into tomorrow. Even though the main part
of the upper level low will remain to our west northwest as it moves east
northeastward, disturbances – like spokes on a bicycle wheel – will rotate
northeastward over our area into the counterclockwise flow around the upper air
low itself.  As these disturbances move through and by the area this afternoon
through tonight and into tomorrow, this will  greatly increase upward atmospheric
lift and will trigger waves of rain showers and thunderstorms and the attendant risk
of severe weather as well as periods of heavier rain.

The threat of severe thunderstorms is present this afternoon through tonight and into
tomorrow. Notice the “enhanced” risk of severe thunderstorms tomorrow in areas
south of Austin tomorrow. See threats area below.

At this point, while we could see upwards of 1 1/2 to 2 1/2 inches or slightly more of rain
and see what I think will be mainly localized urban and low water water crossing effects mainly later
tonight into Friday.

The latest NWS/Weather Prediction Center excessive rainfall guidance for the next
few days says that the best chance of exceeding flash flood guidance should be confined
to areas overhead through south through east of the Austin area proper. The threat of
heavier rain is highest for tomorrow (Friday) into tomorrow night. The weak cold front, that
I’ve been talking about for Friday, now looks like it will be slowed down a bit and will move
through the area Friday night into Saturday. This slower frontal movement will give us
heavier rainfall amounts (thus my numbers, as noted above, are up a bit) and is the reason
that the risk area above has been expanded – as seen below – a little more northwestward
into our area. Here is the latest NWS/Weather Prediction Center excessive rainfall outlook,
expressing the liklihood of rainfall exceeding flash flood guidance, for 7am tomorrow through
7am Saturday..

 

THREAT(S) FOR AUSTIN METRO AND IH35 CORRIDOR COUNTIES:

NWS/Storm Prediction Center Day One Outlook (through 7am Friday): “Slight” Risk of Severe Thunderstorms
Threats: Larger hail.. damaging straight line thunderstorm winds as well as the
presence of deadly cloud-to-ground lightning. The risk of tornadoes is slim.
Geographic area: All of the area
Time Period: Afternoon today into the predawn hours Friday morning.



NWS/Storm Prediction Center Day Two Outlook (7am Friday – 7am Saturday):
“Slight” to “Enhanced” Risk of Severe Thunderstorms
Threats: Larger hail.. damaging straight line thunderstorm winds as well as the
presence of deadly cloud-to-ground lightning. The risk of tornadoes is a little better
in areas south of the Austin area proper.
Geographic area: All of the area
Time Period: Tomorrow through tomorrow afternoon.




MY FORECAST CONFIDENCE:
Weather system evolution: High to very high
Precipitation chances: Increasing to high by afternoon today through Friday
Liquid precipitation (rain) chances: Increasing to high by afternoon today through Friday
Freezing precipitation (freezing rain/freezing drizzle) chances: NONE
Frozen precipitation (snow/ice pellets-sleet) chances: NONE
Thunderstorm/lightning chances: Very high tomorrow this afternoon through Friday
Severe thunderstorm chances: Low to moderate
Flood/Flash Flood chances: Low to moderate (mostly localized urban/low water crossing
flooding) mainly late tonight through tomorrow

AVIATION INFORMATION FOR THE AUSTIN/BERGSTROM
INTERNATIONAL AIRPORT (KAUS) AERODROME:
According to the NWS/Storm Prediction Center, the possibility of severe thunderstorms exists
for much of Texas today through tonight. Main risks for ABIA aerodrome includes
larger hail along with strong straight line thunderstorm wind and the occurrence of deadly
cloud-to-ground lightning. There is much smaller risk of tornadoes and mainly in areas south
of Austin tomorrow. Airport weather warnings (AWWAUS) will likely be issued by the
NWS/Austin-San Antonio this afternoon.. tonight into early Friday as thunderstorms develop
over or move over the aerodrome.

Current KAUS Terminal Aerodrome Forecast (TAF) – Issued 151140z ..

KAUS 161132Z 1612/1718 17010KT 5SM BR VCSH BKN020 BKN040
       TEMPO 1612/1616 BKN009
      FM161700 16012KT P6SM VCSH BKN025
       TEMPO 1620/1624 VRB20G30KT 3SM TSRA BKN020CB
      FM170000 14010KT P6SM VCSH BKN030 PROB30 1700/1704 VRB20G30KT
       3SM TSRA BKN020CB
      FM170400 15008KT P6SM BKN015 OVC050=

. For Our DAL/DFW Hub Aerodromes ..
There is a “marginal” risk of severe thunderstorms for the DAL/DFW aerodromes.
When and if thunderstorms develop or move over the aerodromes this afternoon through
tonight, expect delays and perhaps some diversions.

For Our HOU/IAH Hub Aerodromes ..
There is a “slight” risk of severe thunderstorms for the HOU/IAH aerodromes.
When and if thunderstorms develop or move over the aerodromes this afternoon through
tonight, expect delays and perhaps some diversions.

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.

Today is the day to make sure that your NOAA All Hazards Weather Radios are
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