Air Masses & Fronts Chapter 17 Section 1 Pages Chapter 17 Section 1 Pages

A huge body of air with similar characteristics: Humidity Temperature Air Pressure Classified according to two characteristics: –Temperature- Where did the air mass form? –Humidity- Did the air mass form over water or land? Air Mass

Form over oceans. Water evaporates from the ocean creating humid air. Maritime

Warm air masses form in the tropics and have low air pressure. Tropical

Cold air masses form north of 50°N latitude and south of 50°S latitude. Have high air pressure. Polar

Form over land, in the middle of continents. Very dry air. Continental

Polar Air Masses Maritime Tropical Continental Tropical Maritime Polar Maritime Tropical Maritime Polar

Maritime Tropical mT- originates over a warm tropical ocean. Warm, Moist (humid air) Causes high heat and humidity in the Mid- west and Eastern US. Thunderstorms form due to the moist air and heat available, or heavy rain or snow in the winter. Air Masses

Maritime Polar mP- Originates over the ocean. Cold, Damp (humid) air. Not as cold as cP If cooled to the dew point, precipitation occurs, bring fog, rain and cool temps. Air Masses

Continental Tropical cT- Originates over deserts. Hot and Dry air. Produces tremendous heat waves. Drought like conditions. Air Masses

Continental Polar cP- Originates over Alaska and Canada. Cold and Dry air. Can create precipitation by picking up moisture over the Great Lakes. Air Masses

The Prevailing Westerlies (a major global wind belt) generally push air masses from west to east in the United States. How Air Masses Move

The area where air masses meet and do not mix. Causes storms and changeable weather. Four types. Determined by the characteristics of the air masses and how they are moving. Fronts

A moving warm air mass collides with a slower moving cold air mass. Warm air moves over cold air. (warm air is less dense) Weather- –Clouds, storms and rain. –If humid air, light rain forms. –If dry- scattered clouds form. –After it passes, it is likely to be warm and humid. Warm Fronts

Cold air is very dense and tends to sink. Warm (less dense) air is pushed up. As it rises it cools and forms clouds, may bring heavy rain or snow. Move very quickly, can cause abrupt weather changes including violent T- storms. After it moves through, brings cool, dry air with clear skies and cooler temps. Cold Fronts

Occurs when cold and warm air masses meet, but neither can force the other to move. Water vapor in the warm air condenses into rain, snow, fog or clouds. If it stalls over an area, it can bring these conditions for several days. Stationary Fronts

A complex situation that occurs when a cold front catches up with a warm front. Pushes warm air up over colder air, cutting the warm air off from the ground. Weather- –Ground temp= cool –Brings rain or snowy weather. Occluded Fronts

Surface Map

Cyclone is Greek- meaning “wheel” A swirling center of low pressure. –Spin counter-clockwise (due to coriolis effect winds are turned to the right in the NH) L is short for Low Pressure –Air is moving towards the low –Air is rising, forming clouds and precip. –Bring LOUSY Weather Cyclones

Are areas of high pressure centers Winds spiral out from the center towards areas of lower pressure. –Spin clockwise (due to coriolis effect winds are turned to the right in the NH) H= short for High Pressure –Air is moving away from the high. –Cool air is sinking, and warms as it falls. –Clear, dry weather. (Brings HAPPY weather) Anti-Cyclones

Mid-Latitude Cyclones