Chapter 18: Clouds & Precip.


Chapter 18:1 Clouds & Precip


 Precipitation - any form of water that falls from a cloud.

 Water vapor makes up only 0-4 % of the volume of air.

 3 phases or states of matter(s,l,g)

 6 phase changes - (f&m, e&c, s&d)

Changing state requires that energy is transferred in the form of heat.

Latent Heat=“hidden heat” READ

Evaporation is a cooling process.

Energy must be absorbed …(pool, sweat, energy comes from skin)

 Condensation energy must be released

 violent storms - energy from warm tropical waters.

Humidity=amount of water vapor in air.

 Saturated - air can NOT hold any more water vapor

 Warm air can hold more water vapor than cold air.

 Relative Humidity - ratio of the actual amount of water vapor to how much it can hold at that temperature.

 How to change relative humidity…

 1. Changed by adding or removing water vapor

 2. Change the temperature.

 Lowering air temperature causes an increase in relative humidity.

 Raising air temperature causes a decrease in relative humidity.

 Dew Point - temperature to which air must be cooled to reach saturation or condensation (fog, clouds).

 2 instruments used to measure humidity

1. Hair Hygrometer – uses a hair!

2. Sling Psychrometer - 2 bulbs (one dry one wet)

 High dew point temperatures indicate moist air.

 Low dew point temperatures indicate dry air.

 When the dew point is at or near the actual surface temperature expect humid, cloudy, or foggy conditions.


 Saturation occurs when water vapor is added to air or air is cooled.

 Compressed air warms.

 Expanded air cools.

 Adiabatic Temp. Changes —occur when air is compressed or expanded.

4 Air Lifting Processes:

 1. Orographic lifting = mountains

 2. Frontal Wedging = at fronts the warm air rises over the cooler air.

 3. Convergence = two air masses meet and the result is air rising.

 4. Localized Lifting = warmer pockets of air over parking lots etc. rise


 Stable air (similar temperature top & bottom) does not rise too much thus few or no clouds.

 Unstable air (warmer temperatures at bottom compared to air at top) air rises thus clouds & possibly thunderstorms.

 Radiosonde = weather balloon.

 Temperature Inversions = read it!


18.3 Clouds are classified by form & height.

 Cirrus - (curl of hair) - high, thin, wispy, made of ice. (front approaching)

 Cumulus - (pile/heap) - cauliflower, puffy, smaller ones - fair weather, larger

& darker - thunderstorms.

 Stratus - (layered) - sheets, steady rain to overcast conditions.

 Nimbus - rain clouds(dark gray)

 HIGH - cirro - icy, smaller, thinner

 MIDDLE - alto - medium sized

 LOW - larger

 Vertical Developed Clouds - low to high severe thunder/anvil/cumulonimbus

Unusual Clouds

 Lenticular=lens shaped over mountains

 Heimholtz Waves=uh looks like waves

 Contrails=exhaust of of jets

 Mammatus=light bulb looking clouds

 Anvil Head=cumulonimbus – vertically developed thunder clouds

 Jomammatus=just kidding!

Fog-cloud with base near or at the surface.

 Fog forms from either cooling or evaporation.

 How precipitation forms? (read about it)

 Pages 520-521

 Types of precipitation - snow, sleet, hail, glaze or freezing rain, and rain

How All Clouds Form

1. Warmer air rises .

2. As it gets higher it cools down .

3. As it cools down it reaches its dew point (because cool air can’t hold as much water vapor).

4. Air at its dew point is saturated .

5. Saturated air condenses into water droplets (and they make up clouds).