ST L5: Tornado Characteristics/ Tornado Formation and Evolution

Question 1

What are tornadoes? Where do they come from?

Answer 1

Violently rotating columns of air in contact with the ground. They come from thunderstorms. All VIOLENT ones come from supercell thunderstorms, especially those that are rotating as mesocyclones.

Question 2

How are most tornadoes made visible?

Answer 2

Cloud-water droplets in the funnel cloud and/or by dust and debris from the ground (debris cloud). Some tornadoes are invisible.

Question 3

What is the “tornado alley” region? What is the reason for the high frequency of tornadoes?

Answer 3

Kansas, Oklahoma, Texas.

Good supply of warm humid air (from Gulf of Mexico), favorable wind shear (from southeast at low altitudes and strong jet-stream winds from west at high altitudes). Strong heating of ground during Spring and Summer. Trigger mechanism in the form of cold fronts from Canada and dry lines from west Texas.

Question 4

Favored tornado regions in Canada? Province with highest tornado frequency?

Answer 4

Alberta, southern Sask, southern Manitoba, very southeast corner of Ontario near the Great Lakes of Erie and Ontario. Ontario has highest frequency of tornadoes.

Question 5

What is a tornado outbreak?

Answer 5

A tornado outbreak is when many tornadoes occur during a week or less.

Question 6

What are the two types of motion of tornadoes?

Answer 6

Their translation speed and their rotation speed.

Question 7

Where do tornadoes usually move/translate?

Answer 7

From SW to NE in North America (but movement in any direction has been observed.)

Question 8

What is the translation speed of tornadoes?

Answer 8

the speed that the tornado sweeps across the countryside, tied to the speed that its parent thunderstorm is moving. Translation speeds vary between 0 and 100 km/hr. Most move around 50 km/hr

Question 9

You can easily drive away from tornadoes how?

Answer 9

By driving perpendicular to the tornado track.

Question 10

How to tell if tornado is moving towards you?

Answer 10

If you watch a tornado for a short while and it doesn’t seem to be moving left or right, take immediate shelter, because it might be moving towards you. You won’t recognized that until it is too late.

Question 11

How fast are the rotational/tangential speeds around the tornado center?

Answer 11

They can be faster than 500 km/hr. They are around the tornado center, and are what cause the destruction.

Question 12

What scale classifies tornado intensity in North America? Describe the range of classification.

Answer 12

the Enhanced Fujita scale. It is based only on amount of damage to buildings. So it’s only possible to classify after the tornado has struck. Ranges from EF0 (weak, might break a few windows) to EF5 (super strong, can destroy whole buildings). Can have EF6 and greater, but impossible to determine from damage estimates, because they all cause the same total destruction as an EF5 tornado.

Question 13

EF-0, describe?

Answer 13

65-85 miles/hr wind speeds.

Cause light roof damage. Break off branches. Push over shallowly rooted trees.

Question 14

What % of tornadoes in USA are relatively weak? (EF-0 to EF-1)

Answer 14

75% are EF-0 to EF-1

Question 15

EF-1, describe?

Answer 15

86-110 miles/hr wind speeds. Cause moderate damage such as roofs and severely stripped exterior doors, broken windows, badly damaged mobile homes.

Question 16

EF-2, describe?

Answer 16

111-135 mph wind speeds. torn-off roofs, completely destroys well-constructed houses and mobile homes, large trees snapped, cars lifted off ground

Question 17

What are significant tornadoes?

Answer 17

Tornadoes labelled EF-2 and above.

Question 18

EF-3, describe?

Answer 18

136-165 mph winds. severe damage to well-constructed houses. overturns trains. debarks trees. structures with weak foundations are blown away some distance from original place.

Question 19

EF-4, describe?

Answer 19

166-200 mph winds. completely destroys well-constructed houses. structures with weak foundations are blown away. cars are thrown.

Question 20

EF-5, describe?

Answer 20

over 200 mph wind speeds. Often at impact site, there is nothing there. Strong framed houses lifted off foundations, carried significant distance to disintegrate. even steel-reinforced concrete structures are badly damaged.

Question 21

What is the Torro Scale? What is its downfall? What is its range?

Answer 21

Scale determined by wind speed of tornado, used in Europe. It more precisely quantifies the tornado strength regardless of whether it strikes a building. However, the faster wind speeds in this scale usually cannot be measured because the weather instruments are destroyed. It ranges from T0 (light) to T10 (super).

Question 22

Lifespan of tornadoes usually?

Answer 22

Minutes. Rarely last for hours.

Question 23

How big is their damage path?

Answer 23

Narrow, usually the width of a single house, up to the size of a city block. Rarely have 1 km+ damage path.

Question 24

Safest places to be if a tornado is approaching you?

Answer 24

Below ground in a basement or storm cellar. Some homes in tornado alley have a closet for a “safe room,” made of reinforced concrete walls and ceiling.
If in mobile home, should immediately evacuate if tornado is approaching, either move to a permanent good shelter or get into a ditch.
If outdoors, get into a ditch or hole and place body below the “line of fire” of all the fast moving debris blown by the storm.
If in car, just drive away from tornado on best convenient road, preferably to the right or left of the translation direction of the tornado. Do not hide under a highway bridge or overpass.

Question 25

When are tornado warnings issued? What can detect a tornado?

Answer 25

Only 15 mins or less before tornado hitting, because it is difficult to anticipate them. Doppler radar or human spotter or government official sees a tornado, they issue warning.

Question 26

What is the best a meteorologist can do with a 6-12 hour forecast?

Answer 26

give a Tornado Watch, which indicates a broad region within which tornadoes are favorable or likely later in the day to occur

Question 27

Where do the most violent tornadoes come from?

Answer 27

supercell thunderstorms.

Question 28

What percentage of supercell thunderstorms produce tornadoes?

Answer 28

20-30%

Question 29

Which part of the thunderstorm do tornadoes come from?

Answer 29

the bottom of thunderstorm updraft regions.

Question 30

Which supercells are most likely to generate tornadoes?

Answer 30

Mesocyclones

Question 31

What is the wall cloud? How can that tell us about whether or not a tornado might form?

Answer 31

An isolating lowering of the cloud base, beneath the rising cumulus towers on the southwest flank of the storm. Wall clouds in supercells sometimes rotate, and it is from these rotating wall clouds that tornadoes form. So if there is a wall cloud, a tornado is very likely.

Question 32

What is another unique feature of supercell rotation?

Answer 32

The striations around the mesocyclone.

Question 33

Best place to view thunderstorms?

Answer 33

Off to the side of the storm path. Preferably southeast of the storm, so you can look at the storm toward the northwest, while remaining safe because the storm is not moving toward you (usually).

Question 34

What is a hook echo? Is it a reliable tornado indicator?

Answer 34

Hook shaped radar reflectivity from a partially wrapped rain band around the updraft core (sometimes found, if there is one, then only in a rotating mesocyclone).
Not reliable indicator; it indicates that one of the ingredients for tornado formation is present, by confirming the mesocyclonic rotation.

Question 35

What better evidence for tornadoes can be obtained?

Answer 35

Obtained from the Doppler velocity signal from the weather radar, which measures the speed of the rain-laden air toward or away from radar. In tornadoes, there are fast winds moving away from radar on one side, and fast winds moving toward the radar on the other side, making a distinct signal called a tornado vortex signature.

Question 36

What is a tornado vortex signature? (TVS)

Answer 36

Software in modern weather radars designed to automatically search for and detect TVS and notify meteorologists of its location and movement.

Question 37

Describe tornado life cycle.

Answer 37

1. Beginning stage: funnel cloud (cloud made of water droplets) may not be visible yet, but rotation could already have begun and kicked up dust and debris.
2. Developing stage: If tornado continues to strengthen, the rotating funnel cloud grows down from the base of the thunderstorm.
3. Mature stage: the rotating funnel cloud merges with the debris cloud from the ground.
4. “Rope stage:” Near end of the life cycle, tornadoes often decrease to a “rope” stage, where they are long, thin, and bent or twisted.
5. During the dissipating stage of the first tornado, beware of possible new tornadoes forming nearby.

Question 38

What are waterspouts?

Answer 38

Tornadoes that exist over water. Some come from supercell storms, and can be dangerous to boats. Weaker waterspouts are often cylindrical and look transparent and straw-like. The “debris” cloud for waterspouts is sea spray from ocean surface.

Question 39

What are landspouts?

Answer 39

Weaker tornadoes that form over land, often not associated with supercells. They can also look like soda straws. Tornadoes simulated in tornado machines look like landspouts.

Question 40

What are gustnadoes?

Answer 40

Weak swirls of dust and small debris, often with no water droplet funnel. Look similar to dust devils, but often form along the leading edge of the gust front. They aren’t dangerous.