III.F. Aviation Weather Hazards

Question 1

What are the three stages of thunderstorm development?

Answer 1

Cumulus - Rising air
Mature - Strengthening up and down drafts. Precipitation begins.
Dissipating - Downdrafts dominate, rains itself out.

Question 2

What are the three principal types of thunderstorms?

Answer 2

Single Cell
Multicell
Supercell

Question 3

When flying around convective weather, what are some methods to avoid thunderstorms or the turbulence associated with thunderstorms?

Answer 3

a. NEXRAD for route selection strategy (just remember image may be 15 to 20 minutes old)

b. Listen to chatter on the ATC frequency for PIREPs or deviation requests.

c. Notice buildups out your window. Avoid by at least 20 miles any thunderstorm giving an intense radar echo. This is especially true under the anvil of a large cumulonimbus.

i. Remember that vivid and frequent lightning indicates the probability of a severe thunderstorm.

Question 4

Give some examples of charts and reports useful in determining the potential for and location of thunderstorms along your route.

Answer 4

a. Convective Outlook (AC)— areas of slight, moderate, or high risk of severe thunderstorms for a 24-hour period.
b. Significant Weather Chart (SIGWX)
c. Weather radar
d. Convective SIGMETs (WST)
e. Pilot reports (PIREPs)

Question 5

What are microbursts?

Answer 5

Intense downdrafts which, on reaching the surface, spread outward in all directions from the downdraft center.

Question 6

Where are microbursts most likely to occur? And what is a clue of its existence?

Answer 6

a. Anywhere there is convective activity. They may be embedded in heavy rain or in light rain or virga.
b. A ring of blowing dust may be the only visual clue of its existence.

Question 7

Where is wind shear likely to occur?

Answer 7

It may occur at any level in the atmosphere but three areas are of special concern:
a. Wind shear with a low-level temperature inversion;
b. Wind shear in a frontal zone or thunderstorm; and
c. Clear air turbulence (CAT) at high levels associated with a jet stream or strong circulation.

Question 8

While on a cross-country flight, you notice a lens-shaped cloud over a mountainous area along your route of flight. What does the presence of this type of cloud indicate?

Answer 8

Mountain Wave turbulence

Question 9

What is clear air turbulence (CAT)?

Answer 9

Clear air turbulence is defined as “sudden severe turbulence occurring in cloudless regions that causes violent buffeting of aircraft.”

Often associated with upper level wind shear from the jet stream, or mountain wave.