ATMS 120 Exam 2

Most tornadoes are on the ground for _________ and the current average warning time for tornadoes in the U.S. is ___________.

10 minutes ; 13 minutes

In total, how many severe weather reports does the SPC receive each year in the U.S.?

20,000 - 30,000

If you see lightning and hear thunder 15 seconds later, how far from you was the lightning strike?

3 miles

To what temperature can lightning heat the air that immediately surrounds the bolt?

30,000 C

What is the lowest radar reflectivity value meteorologists used to assume that a radar echo contains hail?

55 dBZ

At what pressure level would you find the level of free convection?

900 mb

At what pressure level would you find cloud base (i.e., the lifting condensation level)?

925 mb

Which of the following is not true with respect to tornadoes?

A funnel cloud is another name for a tornado

Which of the following statements is true about tornadoes?

All 50 states have experienced tornadoes

What is the leading cause for death in a tornado?

Being hit with debris

Heat lightning is caused by...

Distant lightning that is seen but not heard

What time of day are tornadoes most common?

Evening (5-6 pm)

What is the process by which a parcel of air cools as it rises?

Expansion

True or False: A parcel of air will cool at the Moist Adiabatic Lapse Rate if is it rising and has a relative humidity greater than 50%.

False

True or False: Lightning is one of the criteria used by the National Weather Service to determine if a thunderstorm is severe.

False

True or False: Of the three types of thunderstorms we investigated this semester (the ordinary thunderstorm, the mesoscale convective system and the supercell); the supercell is by far the largest storm system.

False

True or False: Positive values of the Lifted Index favor thunderstorms while negative values favor stable conditions.

False

True or False: Since the 1940s lightning fatalities in the U.S. have been relatively constant at around 60 per year.

False

True or False: The "anvil" of a thunderstorm is a low-level cloud that rotates at the base of the supercell thunderstorm

False

Which of the following states has twice as many lightning fatalities than any other state?

Florida

What direction do most supercells track?

From SW to NE

The downdraft of a thunderstorm often produces a cold pool of air that hits the surface and rushes out ahead of the storm. What is the name meteorologists use to describe this feature of the storm?

Gust front

What part of the supercell does the rear flank downdraft create?

Hook echo

Which of the following must a thunderstorm contain to create lightning?

Ice

Which of the following statements best describes how a cloud builds an electrical field capable of producing lightning?

Ice crystals collide with hail stones and graupel and exchange electrons. The ice crystals are then swept to the top of the cloud with a net positive charge, while the hail and graupel remain in the lower part of the cloud with a net negative charge.

To which level in the atmosphere must an air parcel be lifted to in order to get a cloud to begin to form?

Lifting Condensation Level

What is the physical process that occurs in the thunderstorm that produces the sound of thunder?

Lightning heats the air around the bolt which causes a rapid expansion of this air which produces a huge pressure surge that travels as sound wave.

During which stage of thunderstorm development does the downdraft first appear?

Mature Stage

During which month are tornadoes most common in the US?

May

What type of thunderstorm is described here: "A series of thunderstorm cells packed so closely together that each thunderstorm cell is indistinguishable from its neighbor. The leading edge of the convection is a narrow line of intense precipitation that is usually accompanied by fast winds and frequent lightning. Behind these intense thunderstorm cells there is a large trailing stratiform region where light to moderate rain may fall for hours after the main thunderstorm has passed.

Mesoscale Convective System

In which of the following locations are the most tornado fatalities reported?

Mobile homes

Myth or Fact: A person should not be touched immediately after they have been struck by lightning because they carry an electrical charge that could harm you.

Myth

Myth or Fact: If there is a tornado warning for your area, open all of the windows in your apartment or house before taking shelter.

Myth

Myth or Fact: If you are driving on the interstate and a tornado is chasing you, find the nearest overpass or bridge and hide under it.

Myth

Myth or Fact: The movie twister is scientifically sound and is an accurate representation of how tornadoes form and how tornado chasers behave and conduct research.

Myth

Which of the following cities would you want to avoid at all costs if you are terrified of tornadoes because of its history of being hit by tornadoes?

Oklahoma City, OK

Which of the following statements is true with respect to lightning?

On average there are 100 lightning strikes per second on Earth

What meteorological instrument would you use to determine how fast the winds are in a rotating thunderstorm?

Radar radial velocity image

If you were planning on going storm chasing and you wanted to determine if the atmosphere was stable or unstable, what instrument would you use?

Rawinsonde data displayed on a sounding

What does the term "mesocyclone" refer to?

The rotating updraft of a supercell thunderstorm

Which of the following is not true with respect to lightning?

The rubber soles of your shoes will protect you from being struck by lightning.

Which of the following conditions prevented severe thunderstorms from forming?

The surface wind speed and direction matched the wind speed and direction near the tropopause

What typically happens when vortex breakdown occurs?

The tornado becomes very large

Which of the following is not true with respect to the stability of the atmosphere?

The tropopause is an unstable layer in the atmosphere

Which of the following is true with respect to thunderstorms?

Thunderstorm season in the U.S. typically starts in March and lasts through September

True or False: About 75% of the world's tornadoes occur in the U.S.

True

True or False: If you are in the path of a supercell thunderstorm, as the storm approaches you the precipitation would start out as light rain and intensify to moderate rain, heavy rain and then hail. Then, while under the updraft the precipitation would stop and you might see a tornado. As the storm continues on, the rain will briefly intensify again as the hook echo passes over you.

True

True or False: In a negative polarity cloud-to-ground lightning strike, the return stroke creates the bright flash. This bright flash starts from the ground and travels upward into the cloud.

True

True or False: Ordinary thunderstorms are rarely severe because of the lack of wind shear in the environment in which they form.

True

True or False: Supercells always rotate.

True

True or False: Violent tornadoes account for 2% of all tornadoes and 70% of all tornado deaths.

True

What role does vertical wind shear play in the formation of a thunderstorm?

Wind shear can cause the updraft to tilt and separate from the downdraft.

In which of the following situations would the National Weather Service not issue a warning?

hunderstorm winds in excess of 35 mph (30 kts) were reported by an automated surface weather station (ASOS)

During the formation of a tornado within a supercell, the mesocyclone...

is tilted and stretched in the vertical and then squeezed and constricted by the rear flank downdraft which increases the rotational winds by the conservation of angular momentum.

An "adiabatic" process is one where...

there is no mixing of the air within a parcel with the air in the environment