Thunderstorms (CBs)
DefinitionFA violent storm associated with clouds of strong vertival development producing thunder, lightning, heavy showers, hail, gusty wind, turbulence and severe icing.
A. Requirements for Formation
1. unstable air to high levels (30,000 feet)
2. high moisture content in the air
3. a lifting agency to set the air n motion (one of five agenvies)
B. Three Stages of Cell Development
1. Cumulus Stage - 10 to 15 minutes from first radar echo
a) updrafts prevail
b) maximum speed of updrafts occur at the end of this stage (3,000 ft/min
c) diameter of cell grows from 1- 2 miles to a possible 6 miles
2. Mature stage
a) precipitation begins (the onset of pcpn marks the beginning of the mature stage).
b) drag of prercipitation is one cause of downdrafts
c) downdrafts found at all levels except the top (updrafts still occurring)
d) under the CB and ahead of it there may be a roll cloud, formed by friction between up and down drafts
3. Dissipating stage
a) downdraft spreads throughout the cloud
b) precipitation ends
c) "anvil" top becomes marked (caused high winds blowing the top off the cloud)
C. Flight Counditions in a CB or thunderstorm
1. Extent of drafts
a) Cumulus stage - 25,000 feet
b) Mature stage - 40,000 feet
c) Dissipating stage - 10 to 15,000 feet
d) downdrafts are lower down and less in extent than updrafts
e) downdrafts reach a macimum during the mature stage
f) affects the altimetar setting
2. Gusts
a) result of winf shear associated with drafts
b greatest everity 5,000 to 10,000 feet below cloud top. (still severe at surface but not as strong)
3. Hail
a) occurs in mature stage
b) maximum intensity 10 to 15,000 feet
c) if cell is tilted, hail appears to vome from overhanbinb cloud or from clear air
4. ightning
a) can cause structural damage od varying degree
b) greatest frequency between 0Ž and -10Ž
note: The best policy to avoid a CB or THUNDERSTOM !!!!!!!!!!!!!
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