1. Weather Fronts
Air masses are bodies of air that are relatively uniform in temperature and humidity.

2. Air Masses
Air masses take on the characteristics of their geographic place of origin. (please see the bottom of p.13 in your reference table.)
Moist Air Masses (originate from bodies of water) are referred to as maritime.
Dry Air Masses (originate from land) are referred to as continental.

3. Air masses take on the characteristics of their geographic place of origin.
cA: Continental Arctic (came from land in the Arctic region) Winter only.
cP: Continental Polar (came from land located at a high latitude)
cT: Continental Tropical (came from land near/on the equator.)
mT: Maritime Tropical (came from water from near/on the equator)
mP: Maritime Polar (came from water located at a high latitude)

4. Air Masses The temperature is indicated as:
Tropical (originating from areas near/on the equator.
Polar (originating from areas of high latitude)
Arctic (originating from the Arctic circle only seen in the winter)

5. Zone of Convergence
Referred to as a cyclone. Regions of low pressure. Air converges comes together and rises.

6. Zones of Divergence
Referred to as an anticyclone. Regions of high pressure. Cold dry air sinks below warm moist air.

7. Difference between a Cyclone and an Anticyclone
Cyclone: Low pressure, winds move counter clockwise (left)
Anticyclone: High pressure, winds move clockwise (right)

8. Let’s see this

9. Weather Changes occur by the passage of Fronts.
A front is the boundary or interface between two air masses on the ground.
A front forms between two air masses having different temperatures.
Along the frontal surface atmospheric conditions are usually unstable and precipitation is most probable.
Fronts are actually zones of transition

10. Types of Frontal Boundaries
There are four types of frontal boundaries
Warm Front
Cold Front
Stationary Front
Occluded Front
Please see symbols used on p.13 of your reference table.

11. Symbols Used to Represent Fronts

12. Weather Map from April 29, 2010

13. Weather Map from May 2, 2010

14. Reading Weather Maps For current weather map click on the link below.

15.                                                                                                                         
Warm Front
A warm front forms when the warm air (coming from the south) meets and slowly glides up and over the back of cold air.

16. Warm Fronts (continued)
Warm fronts bring mT masses to the north east.
Warm fronts, are preceded by thickening clouds.
Steady rain and fog are common with warm fronts.

17. Cold Front
A cold front forms when cold air pushes into a region of warm air.

18. Cold Fronts (continued)
Cold fronts bring cool, crisp, dry weather. They pass quickly.
Precipitation is intense but brief. Commonly, when the cold front is passing, winds become gusty; there is a sudden drop in temperature, and heavy rain, sometimes with hail, thunder, and lightning
Summer cold fronts bring thunderstorms.
As the front passes, the temperature drops, while air pressure suddenly increases because the cool dry air following the cold front is relatively dense.

19. Comparison of Warm & Cold Fronts
Warm Front
Cold Front
Relative Speed
Temperature Change
Precipitation
Barometric Pressure
Air mass that follows a strong front

20. Stationary Fronts
A front that does not move. There is very little mixing of air.

21. Stationary Fronts (continued)
This happens when two masses of air are pushing against each other but neither is powerful enough to move the other. Winds blowing parallel to the front instead of perpendicular.
The weather is often cloudy along a stationary front and rain or snow often falls, especially if the front is in an area of low atmospheric pressure.

22. Occluded Front

23. Occluded Front (continued)
Sometimes a cold front follows right behind a warm front. A warm air mass pushes into a colder air mass (the warm front) and then another cold air mass pushes into the warm air mass (the cold front). Because cold fronts move faster, the cold front is likely to overtake the warm front. This is known as an occluded front.

24. Occluded Front (continued)
There is often precipitation along an occluded front. Wind changes direction as the front passes and the temperature changes too. The temperature may warm or cool. After the front passes, the sky is usually clearer and the air is drier.
An occluded front ends at a low pressure area shown with a large ‘L’ on the map, and at the other end connects to cold and warm fronts.

25. Occluded Front (continued)
An occluded front does not touch the ground.

26. Storms and Severe Weather
A storm is a violent or severe disturbance of the atmosphere that usually creates dangerous, destructive, or unpleasant conditions on Earth’s surface.
Most storms are associated with high winds, heavy precipitation, fronts, and the low air pressure of cyclonic conditions.

27. Types of Storms Mid latitude cyclones Hurricanes Thunderstorms
Tornadoes
Hail
Blizzards

28. Thunderstorms (continued)
During a thunderstorm, the Earth's surface has a + charge. Because opposites attract, the - charge at the bottom of the thunder cloud wants to link up with the + charge of the Earth's surface.
Once the - charge at the bottom of the cloud gets large enough to overcome air resistance, a flow of - charge rushes toward the earth.

29. Thunderstorms & Lightening
The sky is filled with electric charge. In a calm sky, the + and - charges are evenly interspersed thoughout the atmosphere. Therefore, a calm sky has a neutral charge.
Inside a thunderstorm, electric charge is spread out differently. A thunderstorm consists of ice crystals and hailstones. The ice crystals have a + charge, while the hailstones have a - charge. The ice crystals are pushed to the top of the thunderstorm cloud by an updraft. Meanwhile, the hailstones are pushed to the bottom of the thunderstorm by its downdraft. Thus, the thunderstorm's + and - charges are separated into two levels: the + charge at the top and the - charge at the bottom.

30. Lightening

31. What causes thunder?
Lightning is a giant spark. A single stroke of lightning can heat the air around it to 30,000 degrees Celsius (54,000 degrees Farhenheit)! This extreme heating causes the air to expand at an explosive rate. The expansion creates a shock wave that turns into a booming sound wave, better known as thunder. Thus the name thunderstorm.

32. Hurricanes

33. Hurricanes (continued)
Hurricanes form in the tropics over warm ocean water and die down when they move over land or out of the tropics.
These storms are called hurricanes in the Atlantic and typhoons or tropical cyclones in other areas of the world.
In the Northern Hemisphere the storms rotate counterclockwise and in the Southern Hemisphere they rotate clockwise because of the Coriolis Effect.
At the center of the rotating storm is a small area of calm weather and clear skies called the eye.

34. Tornadoes
Picture of a May 11, 1991, tornado in Cimarron County, Oklahoma

35. Tornados
Tornadoes form from severe thunderstorms. They have a very high energy density which means that they affect a small area but are very destructive to that area.
Tornadoes are caused when a cloud of the right size precipitates rapidly releasing heat. As the heat rises, a vacuum is created under it and air rushes under creating a vortex. Precipitation is faster than evaporation so a very large amount of heat is released when a cloud precipitates.
They also don't last very long which makes it hard to learn about them. Since they're hard to study, they're also hard to forecast.
Tornadoes can occur anywhere in the world. About 75% of them happen in the United States,

36. Blizzards
A blizzard is a storm with large amounts of snow or blowing snow, winds greater than 35 mph (56 kph), and visibility of less than ¼ mile (0.4 km) for at least three hours.

37. What causes a blizzard?
Conditions for a blizzard usually will build up on the northwestern side of a powerful storm system. The strong winds are from the difference in pressures between two systems. This means the difference in the low pressure system which is causing the stormy weather and the high pressure system to the west of the low.

38. Lab Activity #9, Weather Maps
Please complete lab #9: Weather Maps.

39. HW #9, Friday July 23, 2010
Please complete questions on pages and the August 2008 Regent p. 19 #58-61 (you will need to use the answer booklet page 2 for this question).