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Forecasting Weather works0.htm.

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1 Forecasting Weather works0.htm

2 What are Fronts? l A boundary between two air masses is called a __Front_________ l The shape of the _Front_______ depends on the density of the air masses and their speed

3 When a front forms: l Pressure falls when a front approaches (low pressure edges of air masses move in) l Changes in wind direction occur. High pressure air moves Clockwise, low pressure air moves Counterclockwise l Temperature changes occur l Precipitation occurs and can be in the form of strong storms

4 l Low pressure is associated with the formation of clouds and precipitation. l Warm air rises and when it reaches a certain elevation it cools and become saturated. l Clouds form and when they are saturated, it precipitates

5 There are four main types of fronts

6 Warm Front: Warmer air invades a cold air mass and is lifted over and replaces cooler air. Cirrus and stratus clouds are associated with warm fronts Gentle rain for days, slow clearing, and rising temperatures follow

7 Cold Front l Cooler air invades a warm air mass and moves under the warm air and replaces it l Cumulus clouds and thunderstorms produce HEAVY RAIN for a short period of time l Cooler temperatures and l clear and fair weather invade the area once the storms have passed

8 Stationary Front l Occurs when pressure differences cause a warm front or cold front to stop moving l It may remain in the SAME area for a few days. l Weather conditions include light winds and precipitation across the entire frontal region.

9 Occluded Front l Results from two cool air masses merging and forcing warmer air between them to rise l Strong winds and heavy precipitation may occur

10 How do weather systems move? l Weather systems move across North America from West to East.

11 Weather forecasting Making predictions about future weather based on weather data.

12 Weather Maps l Provide data from stations all over the earth l Help meteorologists forecast weather l Data included: –Temperature, air pressure, change in air pressure during the last three hours, wind speed, direction, dew point, visibility, cloud cover, cloud types and precipitation.


14 Isobars l Isobars - pressure lines drawn on weather maps to connect places having equal air pressure. l Isobars that are close together indicate a large pressure difference over a small area

15 Isotherms l Isotherms are lines drawn to connect places having equal temperatures

16 High and Low Pressure l Pressure is indicated in the middle of the isobars l H stands for a high pressure center l L stands for a low pressure center. l Winds develop and move from high to low pressure areas.


18 Technology and Weather Forecasting l Satellites photograph sections of the earths surface and show cloud coverage

19 Air Mass l A large body of air that has the same properties as the surface over which it develops l An air mass over the GULF of MEXICO would be warm and moist l An air mass over CANADA would be cool and dry

20 Air masses l Cool and dry --> high pressure, low humidity CANADA l Warm and moist --> low pressure, high humidity GULF of MEXICO

21 Thunderstorms l Occur inside warm moist air masses and fronts l Result when warm moist air rises quickly and cools and condenses rapidly l Heavy raindrops fall, dragging air with them, creating strong winds l Produced by cumulonimbus clouds

22 Lightning l Atoms of air which are caught in the strong winds lose and gain electrons, creating cloud regions which are positively or negatively charged l Currents flow between these regions resulting in lightning

23 Thunder l Rapid heating and cooling of air due to lightning (rapid expanding and contracting)

24 Tornado l Forms along fronts l Wind at different heights blows in different directions and at different speeds l This along with a strong updraft produces a rotation

25 Hurricanes l A low pressure area develops where the ocean water is very warm l Trade winds blowing in opposite directions meet causing a swirl of air that is rotating l As moist air rises over the low pressure system, it cools and condenses and begins to descend l This pattern is repeated over and over

26 Clouds - condensed water vapor l Recipe for a Cloud: –Water vapor –Condensation nuclei (dust, smoke, ice, salt) –Relative humidity of 100% - saturation point or dew point

27 Types of Clouds: Stratus l fair weather or precipitation l Layers of sheets of clouds, can be dull gray blanket of clouds l Low altitude clouds See pages 425-427

28 Types of Clouds: Cumulus l White puffy clouds with flat bases l Formed when moist air rises l Fair weather or thunderstorms See pages 425-427

29 Types of Clouds: Cirrus l Wispy l High altitude l Contain ice crystals l Fair weather See pages 425-427

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