Transcript Clouds & Pressure Centers

Clouds & Pressure Centers
Clouds: How do they form?
• Clouds – Large collections of very tiny droplets of water or ice
crystals.
• Related to the passing of fronts and air masses.
• Cloud formation:
– All air contains water, but near the ground it is usually in the form of an
invisible gas called water vapor.
– When warm air rises, it expands and cools.
– Cool air can't hold as much water vapor as warm air, so some of the vapor
condenses into tiny pieces of dust that are floating in the air.
– Tiny droplets are formed around each dust particle.
– When billions of these droplets come together, they become a visible
cloud.
Main Types of Clouds: Cirrus
• Found at heights above
20,000 feet.
• Made of ice crystals.
• Form from the freezing of
super-cooled water
droplets.
• White in color.
• Thin and whispy -looking.
• Predict fair weather.
• Predict a change in weather
within the next 24 hours.
Cumulus
• Found at heights above
6,500 feet to 20,000 feet.
• Look like white, puffy pieces
of floating cotton (or
mashed potatoes!)
• Called “fair-weather
clouds.”
Stratus
• Found at heights below 6,500
feet.
• Thin, sheet-like high clouds
that often cover the entire sky.
• So thin that the sun and moon
can be seen through them.
• Often dark in color.
• Usually come 12-24 hours
before a rain or snowstorm
(accompanied with
precipitation).
Cumulonimbus
• Found at heights above
39,000 feet.
• Known as “thunderstorm
clouds.”
• Associated with heavy rain,
snow, hail, lightning, and
even tornadoes.
Pressure Centers: High & Low
• High Pressure –
– Pressure is high relative to its surroundings.
– As you move away from the center of the high pressure
system, the pressure begins to get lower.
– Winds within the high pressure system flow clockwise in
the northern hemisphere and counterclockwise in the
southern hemisphere.
– Associated with fair weather.
• Low Pressure –
– Pressure is lower relative to its surroundings.
– As you move away from the center of the system, the
pressure begins to rise.
– Winds flow counterclockwise in the northern hemisphere
and clockwise in the southern hemisphere.