1. What is the relationship between air temperature and relative humidity?
This graph assumes the amount of water in the air does NOT change as the temperature changes.

2. Think of air as a container, and we need to fit a fixed amount of water into the container.
When the temperature drops, and water vapor amount stays the same, the air fills up with water, increasing the relative humidity.
WARM AIR “container” FITS MORE WATER = 40% humidity
COLD AIR “container” FITS LESS WATER= 90% humidity

3. Aim: Why does the weather change?
Air masses and fronts
Aim: Why does the weather change?

4. Vocabulary: Air mass Source regions Maritime Continental Polar
Tropical
Fronts
Cold Front
Warm Front
Stationary Front
Occluded Front

5. Air masses are…
A volume of air characterized by similar pressure, moisture and temperature.
Air masses acquire their properties from the source region.

6. Source regions are where the air mass comes from
Maritime – from ocean
Continental – from land
Tropical – warm (L)
Polar – cold (H)

9. Air Mass Type
Map Symbol
Formed over….
Characteristics
Continental Tropical cT
Continental Polar cP
Maritime Polar mP
Maritime Tropical mT

10. Naming air masses
Air mass names are characterized by their source regions. Use a 2 letter symbol.
Maritime tropical (mT) – Warm, humid air mass from over tropical oceans. Bring summer showers and thunderstorms, hurricanes
Maritime polar (mP) – Cool, humid air from over cold oceans. Bring fog, rain and cool temperatures, noreasters

11. Continental Tropical (cT) – Hot, dry air from over the Southwest and Northern Mexico
Continental Polar (cP) – Cool or cold, dry air from over Canada and Alaska

12. Warm moist air rises from the equator region, while cool, dry air sinks from the north. These air masses collide over the midwest in early spring causing tornados.
TORNADO ALLEY

13. Fronts – where air masses collide
The warmer air rises above the cooler air. It cools, condenses into clouds and causes precipitation around the front. Fronts signal changing weather, as a new air mass moves into the area.

14. There is always precipitation at a front! Why?

15. 4 kinds of fronts
Symbols (like flags) point in the direction the front and air masses are moving
After the front passes, a new air mass brings new weather conditions

16. Cold fronts Cooler air mass runs into a warmer air mass
Warm air is pushed up rapidly  cumulous clouds and thunderstorms, tornados
Passes quickly, shorter period of rain, heavy downpours
After  clear skies and cooler temps (H -cooler, clearer, drier)
Cold fronts

17. Warm fronts A warmer air mass runs into cooler air mass
Warm air rises over the cold
Passes slowly, clouds over wider area
Slower moving, drizzly or steady rain
After  warm and humid weather (warmer, wetter, cloudier)
Warm fronts

18. Stationary Fronts Cold and warm air masses meet but neither move
“standoff”
Water vapor condenses in the warm air  days of clouds and precipitation until one air mass becomes stronger than the other and begins to move

19. Occluded Front Warm air mass is caught between 2 colder air masses
Cold masses combine and push the warm up
Makes heavy clouds, rain or snow

20. SUMMARY Why does warm air always rise above cool air?
What always happens at a front?
What type of pressure characterizes a air behind a cold front? Warm front?