ATS 351, Spring 2010
Lab #11
Severe Weather – 54 points
Question 1 (10 points): Thunderstorm development
a) Sketch and describe the stages of development of a single cell thunderstorm. About how long
does a single cell thunderstorm last?
Cumulus Stage: storm consists of a single updraft
Mature Stage: storm consists of both an updraft and a downdraft. At this point, drops have
grown large enough to fall out of the cloud. This is the most severe part of the storm.
Development of gust front.
Dissipating Stage: gust front undercuts updraft and suppresses storm growth. Only a downdraft
remains and the storm dies from the bottom up.
b) How does a thunderstorm gust front form? What might you expect to see and feel if a gust
front were to approach and pass you on the ground?
When the cool heavy downdraft air reaches the ground, it spreads out horizontally. The
boundary of this cold downdraft air and the environmental air is the gust front. You would feel a
temperature and dew-point decrease, a pressure increase, an increase in wind strength, and a
wind shift.
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Question 2 (8 points): Types of thunderstorms
In class, we discussed types of thunderstorms. Below each radar image, please identify the
corresponding thunderstorm type it represents (squall line, MCC, single cell thunderstorms or
bow echo).
Figure 1
Figure 1: squall line
Figure 3
Figure3: Bow echo
Figure 2
Figure 2: single cell t-storms
Figure 4
Figure 4: MCC
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Question 3 (10 points): Storm Severity
The two radar images below depict thunderstorms occurring over the U.S.
Figure 3
Figure 4
a) Which Figure shows severe thunderstorms and which ordinary thunderstorms?
Figure 3 shows severe thunderstorms and Figure 4 shows scattered convection over the eastern
U.S.
Below are two soundings.
Sounding 1
Sounding 2
b) Based on lecture, which sounding corresponds best to the environment needed to produce the
storms in Figure 3? Which sounding corresponds best to the storms in Figure 4? EXPLAIN
your reasoning for both answers. HINT: Focus on the air in the troposphere. The wind barbs on
the right hand side are plotted the same way as station plot wind barbs.
Sounding 1 corresponds to the storms in Figure 3 because severe convection requires vertical
wind shear, which is present in Sounding 1. Sounding 2 corresponds to Figure 2 for the opposite
reasoning.
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Question 4 (8 points) : Drylines
The dryline is the boundary between warm, humid air and drier air.
a) On the map below, draw a line where you believe the dryline should be found.
b) Why are drylines favorable locations for thunderstorm formation?
Drylines are boundaries between air masses of different densities, meaning that the less dense air
to the east can ride up over the denser air to the west, leading to convection.
Also (from Ahrens), the elevated western central plains can lead to hot, dry southwest air riding
up and over slightly cooler humid Gulf air, which sets up a potentially unstable atmosphere just
east of the dryline.
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Question 5 (8 points): Tornadoes and Hail
a) What is the first crucial element in the formation of a tornado?
Vertical wind shear
b) What are often mistaken for tornadoes:
funnel clouds
c) What is required for larger hail to exist?
Strong updrafts that transport hail higher in cloud causing interaction with more droplets and/or
the recirculation of hail within cloud due to multiple updrafts
d) What other process does hail aid in a thunderstorm?
Electrification, important in lightning production
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Question 5 (10 points): Surface Map
Below is a surface map with station plots and a low pressure center for April 7, 2010. On the
map, please mark the warm front and the cold front using the appropriate symbols. (Hint:
Remember that fronts are often associated with wind shifts as well as temperature changes.)
Using your knowledge of cyclones, fronts, and severe weather, please circle the location where
you think severe weather is most likely, and explain why you chose this location.
L
Severe weather is most likely in the location circled in black, because it is in the warm sector of
the cyclone. The warm temperatures and moisture in this mT air mass provide fuel for severe
thunderstorms. It is also located near the triple point, which is a common place for severe
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weather. Another possibility for an answer would be along and right ahead of the cold front,
which provides and important source of lift for thunderstorm formation. Here is what actually
happened:
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