Download Weather Forecasts

Weather Forecasts
Weather Dynamics Unit
Science 10
Mrs. S. Pipke-Painchaud
Weather Forecasts
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How do we predict the weather now?
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technology (satellite, radar, computers, etc)
How did people predict weather in the
past?
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daily observations (looking for repeating
patterns
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(Nelson Science 10 543)
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Meteorology:
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Meteorologist:
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“the study of the atmosphere and weather
forecasting” (NS10 543)
People who study weather and work in this
field.
Meteor (Greek)  high in the air
North American Weather Systems
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Equator:
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North Pole:
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Humid and hot, cloudy with sunshine
Cold and dry
Mid-Latitudes are harder to predict
Weather System:
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“a set of temperature, wind, pressure, and moisture
conditions for a certain region that moves as a unit for
a period of days” (NS10 546).
Mid-Latitude areas: air masses move west to east
(mid-latitude westerly winds)
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NS10 546
Air Masses
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“a large body of air in which the temperature and
moisture content at a specific altitude are fairly
uniform” (NS10 546).
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100-1000kms across
Form where air is relatively stable for days or weeks.
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i.e. Cold polar air from the north is dry and cold because little
evaporation occurs in the atmosphere (sun’s rays are at a
low angle)
i.e Warm air from the ocean brings moisture and
precipitation.
Air masses mix via convection and prevailing winds.
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Cold air moves south
Warm air moves north
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NS10 546
Low-Pressure Systems
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Cloudy skies, stormy weather (cyclone counterclockwise)
Refer to page 547 for the stages of a storm
http://nsidc.org/arcticmet/factors/pre
ssure.html
http://en.wikipedia.org/wiki/Image:L
ow_pressure_system_over_Iceland
Stationary Front

When the boundary between a cold and warm
front remains stable for a period of time = stable
weather until the air begins to move

NS10 548
High Pressure Systems
Anticyclone – high pressure system
(clockwise)
 Clear skies
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During the Canadian winter, we experience
cold high pressure systems. The high atm
pressure near the surface occurs as a result
of cold, dry, descending arctic air. Dry air
generally brings clear skies.
(NS10 548)
Air Pressure Demo
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Crushing a pop can:
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http://www.wfu.edu/physics/demolabs/demos/avimov/byalpha/cdvideos.html
Explaining the principles behind it:
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Directions:
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http://www.wfu.edu/physics/demolabs/demos/avimov/byalpha/abvideos.html
Floating Ping Pong Ball Demo:
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http://www.wfu.edu/physics/demolabs/demos/avimov/byalpha/efvideos.html
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Video: Ping Pong Ball in the Funnel:
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http://www.wfu.edu/physics/demolabs/demos/avimov/byalpha/opvideos.html
Audio of Ping pong ball in a funnel:
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http://www.cmste.uregina.ca/Quickstarts/popcancrushing.html
Air Pressure and Paper demo:
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http://littleshop.physics.colostate.edu/Videos/Pressure/pressure%20can/pressurecan.ht
ml
http://amos.indiana.edu/library/scripts/pingpong.html
Atmospheric Pressure Demo Instructions: Read info on large railway tanker
car.
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http://www.delta.edu/slime/cancrush.html
Regional Weather
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Influence globally by:
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Ocean currents
Prevailing winds
Conditions that affect weather in a
localized area.
 i.e.
shore of a lake
 Beside a mountain range
Thermals
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An updraft ~ local convection current
 Sun’s
energy heats the ground, the warm ground
heats the air above it, warm less dense air rises.
The air that moves upward leaves a space for
cooler less dense air to move in at the base. i.e. a
local convection current
 i.e. when you see birds of prey soaring around
high in the air  they are catching rides on thermal
updrafts
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NS10 553
Sea Breezes
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A thermal formed near an ocean or lake.
Land heats and cools faster than water.
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Warm air near land moves out over the cool water and the
cool air over the water moves in over the land (local
convection current).
i.e. cooler near the lake in the summer
i.e. rain near the lake in the winter
Land Breeze:
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A thermal flowing from land to water
Occurs in the evening (water is warm so air rises and
is replaced by the cooler air from the land).
Weak breezes
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NS10 554
Lake – Effect Snow
Air moves across a warm lake in the
winter and picks up moisture.
 When it reaches the cool land on the other
side it snows.
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Cities on the leeward or downwind side of the
lake will receive more snow.
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NS10 554
Chinook Winds
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Occurs east of the rocky mountains
Warm, dry wind
Wind on the west side of the mountains
undergoes orographic lifting, which causes the
water vapour to condense = precipitation.
Condensation = energy release = warm air
Air on the east side of the mountains is dry, but
warm = increase in local temperatures.

“on January 6, 1966, chinook winds raised the
temperature in parts of Alberta by 21 Celsius degrees
in only 4 minutes” (NS10 554).
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NS10 555
Humidity
“a measure of the amount of water vapour
in the atmosphere. . . (also called absolute
humidity)” (NS10 558).
 Relative Humidity:
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“a measure of the amount of water vapour
actually in the air as a percentage of the
maximum amount of water vapour the air
could hold at that temperature” (NS10 558).
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Saturated Air:
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Relative humidity = 100%
Air is holding the max mass of water vapour
Clouds or fog form
Precipitation occurs
Dew
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Forms when at a 100% relative humidity
Dew Point: temp at which dew forms
i.e. condensation occurs when vapour from the air comes into
contact with a surface temperature at or below the dew point.
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The outside of a glass, the mirror in the bathroom, etc.
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NS10 559
Effects of Humidity
Formation of dew
 Sweat:
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Evaporation of water from your body = cools
the body
 High humidity = slower evaporation = you feel
warmer
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Cold temperature contain less water
vapour  therefore, home, school or office
air has less humidity and feels dry.
 What
technology do people use to add humidity to
the air?

Humidifier
(NS10 560)
Sources
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Nelson Science 10 Textbook Chapter 14