Thunderstorms

Question 1

What are the three key ingredients to create a thunderstorm?

Answer 1

• High moisture content
• Steep lapse rate
• A lifting agent

This is why thunderstorms are so frequent in tropical regions

Question 2

How is latent heat important to the development of thunderstorms?

Answer 2

It keeps the air rising past where it otherwise would have stopped.

Latent heat trapped in the water vapor at the surface is released when the warming air rises and cools. This latent heat being released then further warms the cooler air at altitude, causing it to rise, condense, and release its latent heat…etc etc

Question 3

What is the average upward growth rate of clouds in a developing thunderstorm?

Answer 3

5 to 20 meters per second

Question 4

What are the two ways air mass thunderstorms will be stopped from getting any bigger?

Answer 4

• The condensed out water droplets will become so plentiful and heavy that they overcome the updrafts in the form of rain, falling and cooling the air and earth below and preventing further warming and rising
• The rising air reaches the tropopause where the air begins to warm and so cannot rise anymore since the air is warmer.

Question 5

How high can a thunderstorm go?

Answer 5

Depends on the height of the tropopause where the thunderstorm is developing

Question 6

How fast can updrafts and downdrafts be in a mature stage thunderstorm?

Answer 6

Updrafts: 6000fpm
Downdrafts: 2000fpm

Question 7

How long does an air mass thunderstorm’s mature stage usually last and why?

Answer 7

Typically about 15 min, because it chokes itself off so fast. But can last up to an hour.

Question 8

In terms of thunderstorm development, the steeper the lapse rate, the _________

Answer 8

The faster the storm will develop and the higher it will reach.

In the picture, the first bubble of air rises much slower and wont get as high as fast as the bubble of air in the second column.

Question 9

How does dew point affect thunderstorm development?

Answer 9

A higher dewpoint (less of a spread between the temp and dew point) means the air does not have to rise as high to condense out its latent heat and form the cloud base. Because when the cloud forms, the latent heat is released, the air will get another push upward.

So with a higher dew point, there is more room for vertical growth

Question 10

What is a squall line?

Answer 10

• A wall/line of thunderstorms moving in unison.
• Found well ahead of a fast moving cold front
• Depicted on weather map as a line of dots and dashes

Question 11

Where will a squall line’s up/down drafts be most severe?

Answer 11

Along the leading edge of the line

Question 12

Diagram of a squall thunderstorm.

Answer 12

Question 13

Why do squall line type storms last longer than air mass storms?

Answer 13

Because they are moving , the downdraft doesn’t choke off the updraft

Question 14

Where is it most likely for an AC to get struck by lightning?

Answer 14

At altitudes where the temps are between -5 and +5 near thunderstorms

Question 15

How far away can turbulence from a thunderstorm reach?

Answer 15

At least 20NM

Question 16

What do you need to remember about radar displays of thunderstorms and precip?

Answer 16

The the photons emitted by the radar will bounce off of and report only the first bits of water/precip and will not reach, and therefor not report, any storms/precip/clouds behind it

Question 18

What is virga and what does its presence tell us?

Answer 18

Rain that evaporates before it reaches the ground. Associated with micro bursts and to be avoided.

Question 19

What happens to the pressure during a thunderstorm?

Answer 19

Drops while the updrafts are starting and building but then as soon as the rain and downdrafts start the pressure rises sharply

Question 20

Near a thunderstorm the gust front speed and direction may change by as much as….

Answer 20

50kts and 180 degrees in a matter of seconds

Question 21

If overflying a thunderstorm, how high should you go?

Answer 21

1000ft for every 10kts of wind speed at the cloud top

Question 22

What are hurricanes?

Answer 22

• Destructive cyclonic (extreme low pressure system) storms that originate over tropical waters
• Basically huge systems of organized thunderstorms
• Can be 100 miles across or more

Question 23

What is a tornado?

Answer 23

• A rotating cloud connecting a thunderstorm to the ground. Formed when there is a cross wind blowing the updraft of a thunderstorm from the side and spinning it
• Typically only lasts a few minutes but can last several hours

Question 24

How fast do tornados move?

Answer 24

• Average speed is 50km/hr
• Average path of destruction is 3-4 km long
• Wind speed from 65km/hr to 450 km/hr