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 thunderstorms
Thunderstorms
- The warmer and more humid
your environment is throughout the year, the _____ thunderstorms you get
Thunderstorms—Fig. 10-3
Thunderstorm Formation
- You can get a thunderstorm
simply by heating the surface unequally and getting one part so hot that
the air rises on its own
- Also, most of the time, you need
a lifting mechanism like a front to help out
Air-Mass Thunderstorms
- Air-mass T-storms form in
summer ___ air masses in the afternoon and evening and are generally
_______ and short-lived
- A common term for these
storms are "________ thunderstorms"
Regular T-storms--Fig. 10-4
Regular T-storms--See Fig. 10-4
- A regular 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
Regular T-storms--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)
Regular T-storms--See Fig. 10-4
- Without the updrafts, new
moisture cannot rise and condense
- Downdrafts evaporate (80%)
or precipitate (20%) all the moisture, and the storm dissipates
The Good Stuff
- When we have the unequal
heating and the warm, moist, unstable air, but we also have a lifting
mechanism in place (such as a ______), 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 has one or more of the following:
- wind speeds of ___ kts (___ mph) or higher
- hail of diameter ____ in.
or larger
- 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
- 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
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 leading edge of the
_____ _____ is often called the gust front because when it hits, the winds
change __________ and become _________ and ______—brrr!
Gust Front
- Whenever you notice the
temperature _____ sharply when a storm occurs, it usually means the _____
_____ has moved in
- It can provide a brief
respite from ___, _____ summer conditions
Outflow Boundary/Gust Front
Outflow Boundary/Gust Front
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
________ tornadoes are spawned by supercell
thunderstorms
- A supercell
has an average lifetime of _________________ hours
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. 10-20 (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. 10-20 (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. 10-20 (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 cloud base to
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—Fig. 10-18
Wall Cloud
Here Comes the ‘Nader!
Tornado!
Structure
Supercells From Above--Fig. 10-8 (b)
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
Supercells on Radar
Which Storms Are Supercells?
Line of Supercells on Radar
Doppler Radar--Fig. 10-28
Linear Storms
- Supercells
also produce severe damaging ______, even when they don’t have ___________
- Many damaging _____ events
also form from storms that organize into ______
Damaging Winds!
Squall Line Examples
Squall Lines
- Linear severe thunderstorm
development is favored over supercell
development when there is strong favorable ______ shear, but not much
____________ shear
- _____ lines of
strong-to-severe thunderstorms are called squall lines
Squall Line Example
Squall Lines
- Squall lines sometimes form
in advance of _____ fronts or drylines
- Many are long-lived,
lasting ___ or more hours, on average
- Some can persist for more
than a ____!
- As their _____ ______
spread out they create new thunderstorm cells to keep the squall line
going
Cold Pool--New Cells
Squall Line Animation