Thunderstorms!
Tornadoes!
Thunderstorms and
Tornadoes--BWAA
HA HA!
- Chapter 10
- Mult.
Choice Question
Thunderstorms
- Mult.
Choice Answer:
- Thunderstorms form from cumulonimbus
clouds in warm, humid, and __________ environments
- Thus, when it’s _____, we
don’t get as many thunderstorms
- The warmer and more humid your
environment is throughout the year, the _______ thunderstorms you get
Thunderstorms—Fig.
10-3
Thunderstorm Formation
- In addition to the warm, humid
air, we often need a __________ mechanism, such as a ________, to help
lift the air upward to form a thunderstorm
T-storm Life-Cycle--Fig.
10-4
T-storm Life-Cycle--See
Fig. 10-4
- A thunderstorm grows vertically, so at
first it is all updrafts
- Once precipitation forms, it falls
down through the updrafts, causing drag on the air and initiating
downdrafts
T-storm Life-Cycle--See
Fig. 10-4
- Cool, dry air from outside the cloud
is drawn in, causing evaporation of some of the falling precip, which cools the updraft regions and aids
their transformations into downdrafts (cold air sinks)
T-storm Life-Cycle--See
Fig. 10-4
- Without the updrafts, new moisture
cannot rise and condense
- Downdrafts evaporate (80%) or
precipitate (20%) all the water, and the storm dissipates
The Good Stuff
- When we have the warm, moist, unstable
air, a lifting mechanism in place (such as a ______) and favorable
atmospheric _______, we can get more _____________ thunderstorms that
could be more severe and last longer
- Upper-air ____________ also helps
Severe Thunderstorms
- Let’s get right to these severe
thunderstorms
- A thunderstorm is classified as severe
if it produces one or more of the following:
- wind speeds of ___ kts (___ mph) or higher (what the book says is
incorrect)
- hail of diameter ____ in. or larger
(this had previously been 0.75 in., and this again makes the book
incorrect)
- a ________
- About ___% of U.S.
thunderstorms reach severe status annually
Severe Thunderstorms
- Severe thunderstorms usually can
_______ _______ than non-severe thunderstorms
- Why is that?
- Vertical wind shear—changes in
wind ______ and/or __________ with height
Vertical Wind Shear
- When the wind speeds __________ as
height increases, it _____ the thunderstorm
- This results in the precipitation
__________ occurring in different areas than the storm _______
- Thus, the _________ can continue
bringing in warm, moist rising air for longer periods
Tilted
Updrafts—Fig. 10-6
Overshooting Top--See
Fig. 10-6
- When storms contain a great amount of
instability, the air can be rising so fast in the updraft and have so
much momentum, that it can actually break through the tropopause and penetrate into the stratosphere
- That’s when we get the
overshooting top
Overshooting Top Example
Overshooting Top
- If you see an overshooting top,
it’s a signal the storm is very _______ and possibly _______
- What does it mean if you
see…THIS?
Roll Cloud—Fig. 10-7
What Should You Do?
Roll/Shelf Clouds
Roll/Shelf Clouds
- When you see a roll cloud or a shelf
cloud, it is marking the leading edge of the _____ downdraft air that
hit the ground and spread out--pushing out ________ ___ the storm
Roll/Shelf Clouds
- The "_____ _____" spreading out forms
from evaporation of falling precip
________ the air (remember it takes heat to evaporate water)
- At the leading edge of the _____
_____, it acts like a cold front and lifts _____ air up and can create
new thunderstorm cell development
Roll/Shelf
Clouds—Fig. 10-7
Gust Front
- The ____________ edge of the cold pool
is often called the ______ _______ because when it hits, the winds
change direction and become stronger and gusty—brrr!
- Whenever you notice the temperature
_____ sharply when a storm occurs, it usually means the _____ _____ has
moved in
- It can provide a ________ _________
from hot, humid summer conditions
Supercell Picture
Supercells
- ____ thunderstorms are supercells, but a ______ percentage of severe
weather is spawned by supercells—especially
__________ and _____
- The majority of supercells
____ _____ spawn tornadoes, but almost all extremely ________ tornadoes
are spawned by supercell thunderstorms
- A supercell
has an average lifetime of _________________ hours
Supercells--Fig. 10-8 (a)
Supercells
- A supercell
forms when two types of vertical wind shear are present: speed shear
and directional shear
- Speed shear is wind speeds changing
with height
- Favorable speed shear for supercells (and severe t-storms in general) is
wind speeds increasing with height
Speed Shear--Fig. 10-21
(a)
Supercells
- Favorable ____________ shear for supercells is wind directions turning __________
with height
- ___ degrees of turning from
surface to 500 mb is optimal
- We usually achieve this with ________
winds that are SE to S, but quickly turn to SW and to W as height
__________
Supercells
- The directional shear works with the
storm ________ to allow the storm to organize in such a way that the
storm itself _______
- All supercells
exhibit broad _________
Tilting--Fig. 10-21 (b)
Supercells
- A small low pressure center develops
in the middle of the storm, coinciding with the formation of a vertical
column of cyclonically rotating air. This
is called the mesocyclone, or just the "meso"
- Mult. Choice Question:
Supercells
Meso--Fig. 10-21 (c)
Supercells
- One theory for tornado formation is if
the rotation radius can be shrunk (thereby increasing the velocity of
rotation), and it can form all the way from the cloud base to the
ground, you can get the tornado
- Usually before the tornado forms, a
rotating wall cloud will form below the meso,
and the tornado will come out of the wall cloud
Supercell Sketch
Supercell Structure
Supercells
- Most large, damaging _____ comes from supercells as well
- The supercell
_________ are so powerful, they can suspend the ____________, allowing
them to get _______
Supercells
- On radar, look for dark reds and
_________--they may be indicative of large ______
- Also look for a _____ _____--it is
showing a well-defined meso, so it is a
sign a __________ might be there too
Examples of Supercells on Radar
Doppler Radar--Fig. 10-30