1. OBJECTIVE: TO KNOW SEVERAL FACTORS DRIVE CHANGES IN WEATHER. Weather Patterns 11-2

2. The Changing Weather How is weather affected by the movements of air masses and pressure changes? When air masses travel, they can transport heat and water vapor, which can affect weather.  Ex: cool mist air  Cold dry air  Warm moist air  Hot dry air

3. Weather Fronts A cold front: Can move quickly. Thunderstorms often form as warm air is suddenly lifted up over cold air. A warm front: When warm air slides over colder air. This can lead to hours, if not days, of wet weather.

4. Highs and Lows Low Pressure: Recall that when warm air rises, it creates a decrease in pressure close to Earth’s surface. Therefore a low pressure area is created.  Ex: Cloudy stormy weather. High Pressure: When cold air sinks, it moves closer to Earth’s surface and an area of high pressure is created.  Ex: Fair- good weather.

5. Weather Maps Provide info on the atmospheric conditions over any area of interest.

6. Cycles that Affect Weather Day & Night Cycles: As the sun comes up it warms the ground. The ground warms the air by conduction. Sometime in the afternoon the ground and air begin to lose energy and starts to cool. By the evening the or early morning, the coldest air is found next to the ground.

7. Seasons: The tilt of Earth’s axis causes seasons on Earth.  There are 4 seasons.  Fall  Winter  Spring  Summer

8. El Nino:  Both northern hemisphere jet streams shift northward during an El Nino.  In US this often leads to warmer than usual temperatures in the North and increased rain and flooding in the south. La Nina:  Happens when sea surface temps. In the eastern equatorial Pacific are colder than normal.  This produces colder than normal winter temps in the northwestern US.  And warmer than usual winter temps in the southeastern US.

9. Severe Weather Droughts: A period of time when rain is much lower than usual. Can last months to years.  Affects agriculture and can lead to wild fires. Floods: Too much rain fall or rapid snow melt.  Flash floods are the most dangerous because can happen in a instant without warning.