Transcript 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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How did people predict weather in the
past?
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(Nelson Science 10 543)
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Meteorology:
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__________________:
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“the study of the ___________ 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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______________:
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North Pole:
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Humid and hot, cloudy with sunshine
__________ and _____________
Mid-Latitudes are harder to predict
Weather System:
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“a set of _____________, wind, _____________, and
______________ 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 _____________ body of air in which the
______________ and __________ content at a
specific altitude are fairly ______________”
(NS10 546).
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_______kms across
Form where air is relatively stable for days or weeks.
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i.e. Cold polar air from the north is ___________ 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 ________ and
precipitation.
Air masses mix via ____________ and
_______________ 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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___________ skies, ________ 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
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When the boundary between a cold and warm
front remains ________________ for a period of
time = ________________________ weather
until the air begins to move
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NS10 548
High Pressure Systems
__________________ – high pressure
system (clockwise)
 _____________ 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)
Regional Weather
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Influence globally by:
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_
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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 _______________current
 Sun’s
energy heats the ground, the _________
ground heats the air above it, warm less dense air
____________. 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
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NS10 553
Sea Breezes
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A thermal formed near an _________ or ___________.
Land heats and cools ____________ 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. ____________ near the lake in the summer
i.e. ____________ near the lake in the winter
Land Breeze:
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A thermal flowing from ____________ to ____________
Occurs in the evening (water is warm so air rises and is replaced
by the cooler air from the land).
______________ breezes
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NS10 554
Lake – Effect Snow
Air moves across a warm lake in the
winter and picks up _________________.
 When it reaches the cool land on the other
side it _____________.
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Cities on the leeward or downwind side of the
lake will receive _____________ snow.
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NS10 554
Chinook Winds
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Occurs ________ of the rocky mountains
____________, ___________ wind
Wind on the west side of the mountains undergoes
orographic lifting, which causes the water vapour to
____________ = ____________.
Condensation = ___________ release = __________ air
Air on the east side of the mountains is dry, but warm =
increase in local temperatures.
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“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 ____________ of water
vapour in the ____________. . . (also
called absolute humidity)” (NS10 558).
 Relative Humidity:
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“a measure of the amount of water vapour
_______________ in the air as a
_________________ of the maximum amount
of water vapour the air could hold at that
temperature” (NS10 558).
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______________ Air:
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Relative humidity = 100%
Air is holding the max mass of water vapour
Clouds or ____________ form
Precipitation occurs
_____________
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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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________________ of water from your body
= ______________ the body
 ___________ humidity = slower evaporation
= you feel _________________
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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?
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(NS10 560)
Sources
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Nelson Science 10 Textbook Chapter 14