Weather Forecasts Weather Dynamics Unit Science 10 Mrs. S. Pipke-Painchaud

Weather Forecasts How do we predict the weather now? How do we predict the weather now? technology (satellite, radar, computers, etc) technology (satellite, radar, computers, etc) How did people predict weather in the past? How did people predict weather in the past? daily observations (looking for repeating patterns daily observations (looking for repeating patterns (Nelson Science ) (Nelson Science )

Meteorology: Meteorology: “the study of the atmosphere and weather forecasting” (NS10 543) “the study of the atmosphere and weather forecasting” (NS10 543) Meteorologist: Meteorologist: People who study weather and work in this field. People who study weather and work in this field. Meteor (Greek)  high in the air Meteor (Greek)  high in the air

North American Weather Systems Equator: Equator: Humid and hot, cloudy with sunshine Humid and hot, cloudy with sunshine North Pole: North Pole: Cold and dry Cold and dry Mid-Latitudes are harder to predict Mid-Latitudes are harder to predict Weather System: Weather System: “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). “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) Mid-Latitude areas: air masses move west to east (mid-latitude westerly winds) NS NS10 546

Air Masses “a large body of air in which the temperature and moisture content at a specific altitude are fairly uniform” (NS10 546). “a large body of air in which the temperature and moisture content at a specific altitude are fairly uniform” (NS10 546) kms across kms across Form where air is relatively stable for days or weeks. Form where air is relatively stable for days or weeks. 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. 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. i.e Warm air from the ocean brings moisture and precipitation. Air masses mix via convection and prevailing winds. Air masses mix via convection and prevailing winds. Cold air moves south Cold air moves south Warm air moves north Warm air moves north NS NS10 546

Low-Pressure Systems Cloudy skies, stormy weather (cyclone - counterclockwise) Cloudy skies, stormy weather (cyclone - counterclockwise) Refer to page 547 for the stages of a storm Refer to page 547 for the stages of a storm ow_pressure_system_over_Iceland.jpg ssure.html

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 When the boundary between a cold and warm front remains stable for a period of time = stable weather until the air begins to move NS NS10 548

High Pressure Systems Anticyclone – high pressure system (clockwise) Anticyclone – high pressure system (clockwise) Clear skies Clear skies 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. 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 Crushing a pop can: Explaining the principles behind it: ml ml Directions: Air Pressure and Paper demo: Floating Ping Pong Ball Demo: Video: Ping Pong Ball in the Funnel: Audio of Ping pong ball in a funnel: Atmospheric Pressure Demo Instructions: Read info on large railway tanker car.

Regional Weather Influence globally by: Influence globally by: Ocean currents Ocean currents Prevailing winds Prevailing winds Conditions that affect weather in a localized area. Conditions that affect weather in a localized area. i.e. shore of a lake i.e. shore of a lake Beside a mountain range Beside a mountain range

Thermals An updraft ~ local convection current 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 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 i.e. when you see birds of prey soaring around high in the air  they are catching rides on thermal updrafts NS NS10 553

Sea Breezes A thermal formed near an ocean or lake. A thermal formed near an ocean or lake. Land heats and cools faster than water. Land heats and cools faster than water. 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). 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. cooler near the lake in the summer i.e. rain near the lake in the winter i.e. rain near the lake in the winter Land Breeze: Land Breeze: A thermal flowing from land to water 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). Occurs in the evening (water is warm so air rises and is replaced by the cooler air from the land). Weak breezes Weak breezes NS NS10 554

Lake – Effect Snow Air moves across a warm lake in the winter and picks up moisture. 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. When it reaches the cool land on the other side it snows. Cities on the leeward or downwind side of the lake will receive more snow. Cities on the leeward or downwind side of the lake will receive more snow. NS NS10 554

Chinook Winds Occurs east of the rocky mountains Occurs east of the rocky mountains Warm, dry wind Warm, dry wind Wind on the west side of the mountains undergoes orographic lifting, which causes the water vapour to condense = precipitation. Wind on the west side of the mountains undergoes orographic lifting, which causes the water vapour to condense = precipitation. Condensation = energy release = warm air Condensation = energy release = warm air Air on the east side of the mountains is dry, but warm = increase in local temperatures. 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). “on January 6, 1966, chinook winds raised the temperature in parts of Alberta by 21 Celsius degrees in only 4 minutes” (NS10 554). NS NS10 555

Humidity “a measure of the amount of water vapour in the atmosphere... (also called absolute humidity)” (NS10 558). “a measure of the amount of water vapour in the atmosphere... (also called absolute humidity)” (NS10 558). Relative Humidity: Relative Humidity: “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). “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).

Saturated Air: Saturated Air: Relative humidity = 100% Relative humidity = 100% Air is holding the max mass of water vapour Air is holding the max mass of water vapour Clouds or fog form Clouds or fog form Precipitation occurs Precipitation occurs Dew Dew Forms when at a 100% relative humidity Forms when at a 100% relative humidity Dew Point: temp at which dew forms 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. i.e. condensation occurs when vapour from the air comes into contact with a surface temperature at or below the dew point. The outside of a glass, the mirror in the bathroom, etc. The outside of a glass, the mirror in the bathroom, etc. NS NS10 559

Effects of Humidity Formation of dew Formation of dew Sweat: Sweat: Evaporation of water from your body = cools the body Evaporation of water from your body = cools the body High humidity = slower evaporation = you feel warmer High humidity = slower evaporation = you feel warmer Cold temperature contain less water vapour  therefore, home, school or office air has less humidity and feels dry. 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? What technology do people use to add humidity to the air? Humidifier (NS10 560) Humidifier (NS10 560)

Sources Nelson Science 10 Textbook Chapter 14 Nelson Science 10 Textbook Chapter 14