Changing Weather From: Ck-12.org Foundation Earth Science Chapter 16 By: Robert Smith

weather in a location often depends on what type of air mass is over the location A key factor is whether the spot is beneath a front, the meeting place of two air masses characteristics of the air masses and their interactions determine whether the weather over an area is constant, or whether there are rapid changes

Air Mass air mass is a batch of air that has nearly the same temperature and humidity air mass acquires characteristics above an area of land or water known as its source region air mass that sits over a region for several days, or longer, it picks up the distinct temperature and humidity

Air Mass Formation Air masses form over a large area Air masses form primarily in high pressure zones, most commonly in polar and tropical regions Temperate zones are ordinarily too unstable for air masses to form air masses move across temperate zones so the middle latitudes are prone to having interesting weather

cPk symbol cPk is an air mass with a continental polar source region that is colder than the region it is now moving over

Air Mass Movement Air masses are slowly pushed along by high- level winds temperature and humidity of a particular location depends partly on the characteristics of the air mass that sits over it cold air masses tend to flow toward the equator and warm air masses tend to flow toward the poles

Fronts Two air masses meet at a front the two air masses have different densities and do not easily mix One air mass is lifted above the other, creating a low pressure zone If the lifted air is moist, there will be condensation and precipitation. Winds are common

Four Types of Fronts stationary front the air masses do not move may bring days of rain, drizzle, and fog Winds usually blow parallel to the front, but in opposite directions

Cold Fronts a cold air mass takes the place of a warm air mass, there is a cold front squall line is a line of severe thunderstorms that forms along a cold front. Behind the front is the cold air mass

Cold fronts vary by season spring and summer: The air is unstable so thunderstorms or tornadoes may form. spring: If the temperature gradient is high, strong winds blow. autumn: Strong rains fall over a large area. winter: The cold air mass is likely to have formed in the frigid arctic so there are frigid temperatures and heavy snows.

Warm Front a warm air mass slides over a cold air mass

Occluded Front occluded front usually forms around a low pressure system starts when a cold front catches up to a warm front air masses, in order from front to back, are cold, warm, and then cold again If the air mass that arrives third is colder than either of the first two air masses, that air mass slip beneath them both. This is called a cold occlusion

Images of Weather