Homework Questions #4:Answers
1. An unstable environment, one in which thunderstorms are likely to form, will be
____much warmer___ at the surface than at upper-levels (steep environmental lapse
rate). In his way, rising air parcels stay ____warmer____ than their environment (are
very “bouyant”) and thus rise quickly, creating a vigorous updraft.
2. What about the properties of the environment at the tropopause causes it to act like a
“lid” to this rising motion?(see the top of page 5 – II B 4. f. 2)
As we reach the tropopause, the environment changes its temperature structure from decreasing with height (troposphere) to increasing with height (stratosphere). Therefore, as our rising air parcels hit the tropopause and move into the stratosphere (where the environment warms with altitude) the air parcel will suddenly become colder than the surrounding environment and sink back down to the troposphere
3. What are the three environmental conditions necessary for thunderstorms to form?
1. Lifting mechanism
2. Instability
3. Low-level moisture
4. Ordinary (airmass) thunderstorms do not last long because, since they do not form in the
vicinity of the jet stream, they have an ____upright____vertical configuration causing
the___downdraft____ to be superimposed on the ____updraft____.
5. Why are mesoscale convective systems (MCSs) [systems of grouped thunderstorms] so
critical to human life (in a positive way)?
They provide the majority of the rainfall necessary in agricultural regions during the growing season
6. Why do these groups of thunderstorms last so much longer than ordinary
thunderstorms?
Because the updraft becomes tilted so that the downdraft is not superimposed on it
7. Thunderstorms are designated “severe” if they generate any one of what three
conditions?
1. Hail with 3/4 inch diameter or more
2. Winds in excess of 50 knots (58 mph)
3. A tornado
8. _____Supercell_____ thunderstorms are by far the most intense and generate the
vast majority of violent tornadoes.
9. In question #3, note was made of three environmental conditions necessary for
thunderstorms to form. What is the fourth condition which enables “extreme” (question #7) thunderstorms to form?
Strong vertical wind shear (wind increasing rapidly in speed and changing direction with altitude)
10. This fourth requirement necessitates that these thunderstorms form in the vicinity of
____extratropical cyclones and the polar front jet stream_____ .
11. This fourth requirement enables the storm to tilt and ____rotate_____, separating
the updraft from the downdraft and setting the stage for tornado formation.
12. These storms tend to form in the “______warm_____ sector” of ECs, between the cold
front (or dryline) and warm front.
13. These four conditions, all superimposed in large quantity, are relatively unique to
_____Great Plains and Midwest of the U.S._______ (geographical location) during _____Spring_____ (season) which make these extreme storms more numerous in this region than anywhere else in the world.
14. What is the fifth condition, also unique to this location, which contributes to the
formation of these storms by serving like a “lid on a boiling pot”?
Capping inversion
15. The rotating updraft of one of these thunderstorms is called the ___mesocyclone____.
16. The rotating cloud from which a tornado may eventually descend toward the ground is
called a _____wall cloud______.
17. Not much is known about tornado formation. What are thethree reasons that they are
difficult to study?
1. They are rare
2. Exactly where they will occur is difficult to predict
3. For safety reasons, they are difficult to get close to
18. The scale to categorize tornadoes based on the damage incurred by the winds is called
the ______Fujita (F)______or ______“Enhanced” Fujita (EF)______scale.
19. ___EF4___ and ___EF5__ tornadoes (~2% of all tornadoes) are responsible for 70% of
tornado deaths.
20. “Tornado alley” is located where?
Southern Great Plains of the U.S.
21. The majority of tornadoes occur in this region (tornado alley) during what season?
Spring
22. During what time of day do tornadoes peak?
Late afternoon to evening
23. The radar hook echo is indicative of a ____supercell thunderstorm_____. Doppler
radar detects _____rotation_____ in a thunderstorm.
24. A tornado watch means ____conditions are right (conducive) for tornado formation______.
A tornado warning means ____a tornado has been spotted or rotation is identified in a____
______thunderstorm by Doppler radar_____.
25. Hail stones grow by collecting ______supercooled water droplets______as they
get pushed up and down by the updraft and downdraft in a thunderstorm.
26. What is the most importantimpact of hail?
Crop damage
27. a) There has been a(n) ____increase____ in reported tornadoes since 1950?
b) What is the likely reason for this?
Most likely because of a marked increase in tornado awareness, increased population in areas where tornadoes occur and storm spotters
28. There has been a(n) ____decrease____ in violent (F3 – F5) tornadoes since 1950?
29. a) There has been a(n) ___decrease___ in tornado deaths since the early 20th century?
b) Why?
Most likely due to increased tornado awareness, improved tornado forecasting and warning systems, and better construction
30. The change in violent tornadoes with global warming to this point and the likely change
in atmospheric conditions necessary for tornado formation with further warming suggest a possible _____decrease_____ in supercell thunderstorm and tornado formation in the future.
31. Given the scale and complexity of tornado formation, as well as our limited
understanding of their behavior, any projection of change in number and intensity of these features in the warmer climates of the future is ____speculative____ at best.
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