Name: _________________________________________________ Date: ________________ Period: _______
18.2 Cloud Formation
I. Air Compression & Expansion

Adiabatic Temperature Changes:
– Occur when ______________________________________________________________________
– Done by _________________________ change: air expands or contracts
 Expansion = __________________________
 Compression = _________________________

Expansion and Cooling:
– Air pressure ____________________________ as you____________________________ elevation
– Dry adiabatic rate: for _____________________ air
 Temp. ___________________ 10°C for every 1000 m it moves _______________________
(______________________________________)
 Temp. ____________________ 10°C for every 1000 m it moves ______________________
(______________________________________)
– Wet adiabatic rate: for ___________________________ air
 Temp. changes _______________________ per 1000 m
 Slower because of ______________________________
– Air at the _________________________ will release latent heat as it ____________
and water ________________________; this works against the cooling.
– Rate varies because amount of moisture in the air varies
 Important for determining _____________________________________________________
____________________________________________________.
II. Processes That Lift Air

Orographic Lifting: occurs when __________________________________________________________
_____________________________________________________________________________________
– The forced rise causes adiabatic ___________________ that generates clouds and precipitation
– The air ____________ adiabatically as it _______________ down the other side, making
condensation and precipitation less likely.
 This is why the __________________________ sides of mountains are some of the
_____________________________ places on earth while the ____________________ sides
are some of the _________________ (“_________________________________________”).

Frontal Wedging: occurs when ____________________________________________________________
_____________________________________________________________________________________
– The __________________________________________ air acts as the barrier that forces the
________________________________ air to rise.

Convergence: occurs when _______________________________________________________________
– Rising air ___________ adiabatically, possibly forming clouds
– Common over _________________________ like Florida: air from the Gulf meets air from the
Atlantic over land

Localized Convective Lifting: occurs when __________________________________________________
_____________________________________________________________________________________
– _____________ use them to gain altitude; people use them for _____________________________
– When the pockets ___________, they often form _________________________
III. Stability

Stable air: a pocket of air _______________ and __________________ than the surrounding air that
resists ________________________________________

Stable air tends to _______________________________________________________, while unstable air
(warmer than the surrounding air) tends to ______________
– This is how ____________________________________ work.



Normally, air temperature ___________________________ gradually with ________________________
altitude; when the temperature increases with height, it is called a ________________________________
__________________________.
– This is when the most _______________ conditions happen.
– Usually happens on ______________________________
Clouds associated with stable air are ____________________________________________________,
with little if any precipitation.
Clouds associated with unstable air masses often generate ___________________________________ and
the occasional ____________________________.
IV. Condensation

For any form of ________________________________ to occur (dew, fog, or clouds), the air must be
_____________________________.
– Usually when air is cooled to its _________________________

Water vapor must have a ____________________ to condense upon.
– In the air, tiny bits of particulate matter called __________________________________________
serve as the surfaces for water vapor condensation.
 Ex: _______________________________________________
 Without them, relative humidity over 100% would be necessary for clouds.