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Weather
Weather is the state of the
atmosphere at any given time
or place.
Climate
Climate is the average weather conditions that
occur in a region over a long period of time.
How is weather measured
and described?
• Temperature (0C)
• Precipitation (mm for rain) (cm for snow)
• Atmospheric Pressure or Air Pressure (kPa)
• Wind (km/hr)
• Relative Humidity (%)
• Clouds (type)
• U.V. Sunlight Rating (1 low to 11 extreme)
Atmospheric Pressure
The amount of force pushing on you due to the
weight of the air.
High and Low Pressure Systems
When the air is compressed it is under “high
pressure”.
Weather forecasters measure air pressure with a
Barometer.
Standard Atmospheric Pressure is 101.325 kPa
Atmospheric Pressure and
Weather
Air pressure can tell us about what kind of
weather to expect as well.
If a high pressure system is on its way,
you can expect cooler temperatures and
clear skies.
If a low pressure system is coming, then
look for warmer weather, storms and rain.
Wind
Wind is air that is moving from a high
pressure system to a low pressure system.
The spinning of the Earth also creates wind
(The Coriolis Effect). This causes the
prevailing westerly winds in North
America.
Clouds
Most clouds are associated with weather.
They are divided into groups based on the
height of the cloud’s base about the
Earth’s surface.
High Clouds (“Cirr”)
• 5 000 – 13 000m
• made of ice crystals due to the cold air in the
•
upper sky
not really associated with daily weather
Middle Clouds (“Alto”)
• 2 000 – 7 000m
• Altostratus – covers whole
sky, blue-gray appearance.
They usually form ahead of
storms with continuous rain
or snow.
• Altocumulus – form in groups
(grayish-white). They are
about as wide as your thumb
when you hold up your hand
at arm’s length. If you see
them on a warm humid
morning, expect
thunderstorms by afternoon.
Low Clouds (“Strat”)
• Surface – 2 000m
• Stratus – look like a fog that doesn’t reach the ground. Light
•
•
mist or drizzle is sometimes associated with these clouds.
Stratocumulus – are low, lumpy and gray. They can look like
cells under a microscope.
Nimbostratus – dark gray with a “ragged” base. They are
associated with continuous rain or snow.
Clouds with Vertical Growth
(“Cumu”)
• Surface – 13 000m
• These clouds grow high
•
•
up into the atmosphere
rather than spreading
out.
Cumulus – cloud puffs
that are about the size
of your fist when you
hold up your hand at
arm’s length.
Cumulonimbus –
thunderstorm clouds