Weather Clouds and Precipitation
Have you ever just looked at clouds? • Why do we have clouds? • Why are there different shapes? • What can they tell us about the weather?
Take Good Notes! • There will be a quiz on this information
Understanding Clouds • Clouds form as warm air is forced upward • As the air is forced upward, it expands and cools
Fronts and Air Masses • An air mass is a large body of air whose temperature and moisture are fairly similar at a given altitude • Fronts are boundaries separating different air masses • There are four different air masses that affect the United States
The Air Masses • cP( continental polar) : cold, dry stable • cT( continental tropical) : hot, dry, stable air aloft, unstable at the surface • mP( maritime polar) : cool, moist, unstable • mT( maritime tropical) : warm, moist, unstable
Ok, now we see the difference in the air masses • Let’s look at the different fronts and their impact on weather • Can you see the four different types of fronts on the map?
Warm Fronts • A warm front is warm air displacing cool air diagram • Shallow leading edge warm air must “overrun” cold air • These are usually slow moving
Cold Fronts • Cold air advances into region of warm air • Intensity of precipitation greater, but short lived • Clearing conditions after front passes • Usually approaches from W or NW
Stationary Fronts • Surface positions of the front do not move • Often a region of clouds
Occluded Fronts • Cold front overtakes warm front • Often found close to the low pressure center
Pressure’s Affect H L L
W R E C C C CloudsCondensesCoolsExpandsRisesWarm Air
How Else Can Clouds Form? • Fronts: When a WARM FRONT RISES OVER A COLD FRONT. This produces non violent rain showers.
Fronts: When a COLD FRONT RISES OVER A WARM FRONT. This produces possibly violent rain storms very quickly, but is brief and may last only part of the day.
Before Cold Front After Cold Front
Orographic Uplift: When air is forced up the side of a mountain or plateau. The air forced up then cools down very quickly and condenses to form rain clouds.
Understanding Clouds • As the air cools, the relative humidity reaches 100% • For more information on Relative Humidity click ☼
Water vapor begins to condense in tiny drops around nuclei. Nuclei are small particles of dust, salt, and smoke in the atmosphere
Cloud Types • There are many different cloud types
Cloud Types • Can you think of the two main ways that clouds are classified? • Shape, Height, and sometimes RainCapacity
By Shape! • There are three main cloud types that are based on shape • Think you know any of them? • Stratus • Cumulus • Cirrus
Stratus Clouds • Stratus clouds form a smooth, even sheet • They usually form at low altitudes
Stratus Clouds • When air is cooled and condenses near the ground, a stratus cloud know as _______ forms • Know the name?
Fog • Fog forms when a cold surface cools the warmer moist air above it. • What is water vapor doing in the air to form fog? • Condense • At what temperature does the air hit to condense as fog? • Dewpoint
Cumulus Clouds • These are masses of puffy, white clouds, often with flat bases • They form when air currents rise
Cumulus Clouds • They can be associated with both fair weather and…….when they get really tall!?!?!
Cirrus Clouds • Cirrus clouds are high, thin, white, feathery clouds containing ice crystals
Cirrus Clouds • Cirrus clouds are usually associated with fair weather, but they may indicate approaching storms
By Height • The prefix of cloud names can describe the height of cloud bases • Cirro: High clouds above 6000m
By Height • Alto: Middle elevation clouds between 2000 to 6000m • Strato: Low level clouds below 2000m
Rain Clouds • Nimbus clouds are dark clouds associated with precipitation
Rain Clouds • When a nimbus cloud is also a towering cumulus cloud, it’s called a cumulonimbus cloud
Ready for a quick review? • 1. Clouds can form when the relative humidity reaches ____% • 2. In order for clouds to form, water vapor begins to condense around ____of dust, salt, and smoke
3. Clouds are classified by ____ and____ and sometimes rain capacity • 4. Puffy, white clouds are called? • 5. Mid elevation clouds between 2000 and 6000m
Let’s see how you did! • 100 • Nuclei • Shape and height • Cumulus • Alto
Forms of Precipitation • Precipitation (pre-sip-uh-tay-shun) is any form of water that falls to the Earth's surface.
Types of Precipitation • The type of precipitation that falls to the ground depends upon the formation process and the temperatures of the environment between the cloud and the surface
Can you name the different types of precipitation? • Rain • Snow • Hail • Sleet • Freezing Rain
Rain • Rain develops when growing cloud droplets become too heavy to remain in the cloud and as a result, fall toward the surface as rain
Rain can also begin as ice crystals that collect each other to form large snowflakes As the falling snow passes through the freezing level into warmer air, the flakes melt
Snow • Snow is formed when ice crystals form from water vapor that is in the clouds directly above your heads! • This process is called sublimation