Weather Patterns Severe Storms Chapter 20 20 1

Weather Patterns & Severe Storms Chapter 20

20. 1 and 20. 2

• a large body of air that has the same temperature and humidity throughout • classified according to where they originate • during the time the air mass is over an area, it determines the weather of that area

As an air mass moves away from where it formed and into a new area, it carries its temperature and moisture conditions with it. Example: Frigid Canadian Air Mass

Classifying Air Masses Source Region: the area over which an air mass gets its characteristic properties of temperature and moisture. There are 4 source regions used to name air masses…

1. Originates over the ocean Maritime: humid air mass (m)

2. Originates over the land Continental: dry air mass (c)

3. Originates in cold air Polar: cool air mass (P)

4. Originates in warm air Tropical: warm air mass (T)

Maritime Tropical Atlantic (m. T) • moves northward across eastern United States • brings mild & cloudy winters and hot & humid summers with hurricanes & thunderstorms

Fronts: boundary between two air masses having different temperatures and humidity

• Warm air moves into an area formerly covered by cooler air • warm air gradually rises & cools to produce clouds • brings hot, humid days and light-to-moderate precipitation over a large area

Warm Front Animation

• Cold, dense air moves into a region occupied by warmer air • Form and advance rapidly, forcefully lifting air • Brings heavy downpours and gusty winds (squalls) followed by clear cold air (high pressure)

Cold Front Animation Cold Front vs. Warm Front

• When an active cold front overtakes a warm front • Cold air wedges the warm front upwards • Complex weather results…may start with heavy rain and strong wind as warm front is lifted, then shift to long period of light rain

• Surface position of the front does not move • Air on either side of a front moves parallel to the front • Gentle to moderate precipitation

• small-area storms formed by the strong upward movement of warm, moist, unstable air • always accompanied by lightning, thunder, and usually rain • formed from cumulonimbus clouds

Observe an animation of a thunderstorm.

Air-mass thunderstorm: • form in warm, moist air mass • occur in spring and summer- last less than 1 hour • single, widely scattered