Weather Forecasts

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

2. Weather Forecasts • How do we predict the weather now? • How did people predict weather in the past? • (Nelson Science 10 543)

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

4. North American Weather Systems • ______________: • Humid and hot, cloudy with sunshine • North Pole: • __________ and _____________ • Mid-Latitudes are harder to predict • Weather System: • “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) • NS10 546

5. Air Masses • “a _____________ body of air in which the ______________ and __________ content at a specific altitude are fairly ______________” (NS10 546). • _______kms across • Form where air is relatively stable for days or weeks. • 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. • Cold air moves south • Warm air moves north • NS10 546

6. Low-Pressure Systems • ___________ skies, ________ weather (cyclone - counterclockwise) • Refer to page 547 for the stages of a storm http://nsidc.org/arcticmet/factors/pressure.html http://en.wikipedia.org/wiki/Image:Low_pressure_system_over_Iceland.jpg

7. Stationary Front • When the boundary between a cold and warm front remains ________________ for a period of time = ________________________ weather until the air begins to move • NS10 548

8. High Pressure Systems • __________________ – high pressure system (clockwise) • _____________ 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)

9. Regional Weather • Influence globally by: • _ • Conditions that affect weather in a localized area. • i.e. shore of a lake • Beside a mountain range

10. Thermals • 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 • NS10 553

11. Sea Breezes • A thermal formed near an _________ or ___________. • Land heats and cools ____________ 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). • i.e. ____________ near the lake in the summer • i.e. ____________ near the lake in the winter • Land Breeze: • 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 • NS10 554

12. 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 _____________. • Cities on the leeward or downwind side of the lake will receive _____________ snow. • NS10 554

13. Chinook Winds • 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. • “on January 6, 1966, chinook winds raised the temperature in parts of Alberta by 21 Celsius degrees in only 4 minutes” (NS10 554). • NS10 555

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

15. ______________ Air: • Relative humidity = 100% • Air is holding the max mass of water vapour • Clouds or ____________ form • Precipitation occurs • _____________ • 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. • The outside of a glass, the mirror in the bathroom, etc. • NS10 559

16. Effects of Humidity • Formation of dew • Sweat: • ________________ of water from your body = ______________ the body • ___________ humidity = slower evaporation = you feel _________________ • 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? • (NS10 560)

17. Sources • Nelson Science 10 Textbook Chapter 14