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Weather!Weather!

Matt AufmanMatt Aufman

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November 2005November 2005

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Temperature• You will usually see temperature measured in °F for maps of the United States

• Maps of foreign countries will usually be measured in °C

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Relative Humidity• The relative humidity tells us how “full” the air is at the time of measurement.

• For example, 90% relative humidity means that at that moment the air is holding 90% of the maximum amount of water it could.

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Cloud Cover Symbols• You will often see the circles drawn on a weather map

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High and Low Pressure Areas

• High pressure causes air to sink

• Usually results in several days of clear sunny skies

• Air rises in low pressure areas and forms water droplets

• Usually results in rain and storms

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Air MassesThere are two types of air masses:

1. Continental Polar air masses

2. Maritime Tropical air masses

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Fronts

A front is the boundary separating air masses of different densities

Fronts extend both vertically and horizontally in the atmosphere

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Fronts: Five Types of Fronts1. Cold Front: The zone where cold air is replacing warmer air

• In U.S., cold fronts usually move from northwest to southeast

• Air gets drier after a cold front moves through

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Fronts: Five Types of Fronts2. Warm Front: The zone where warm air is replacing colder air

• In U.S., warm fronts usually move from southwest to northeast

• Air gets more humid after a warm front moves through

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Fronts: Five Types of Fronts3. Stationary Front: When either a cold or warm front stops moving

• When the front starts moving again it returns to either being a cold or warm front

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Fronts: Five Types of Fronts4. Occluded Front: Formed when a cold front overtakes a warm front

• This occurrence usually results in storms over an area

• In U.S., the colder air usually lies to the west

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Fronts: Five Types of Fronts5. Dry Line (Dew Point Front): Boundary separating a dry air mass from a moist air mass

This occurrence can result in tornadoes being formed

Usually found in western part of U.S.

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Clouds: Five Types of Clouds1. High-Level Clouds: Usually found at greater than 20,000 ft.

Usually made of ice crystals

Examples include Cirrus, Cirrostratus

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Clouds: Five Types of Clouds2. Mid-Level Clouds: Usually found between 6,500 and 20,000 ft.

Usually made of water droplets, but can be made of ice

Example is altocumulus

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Clouds: Five Types of Clouds3. Low-Level Clouds: Usually found lower than 6,500 ft.

Low, lumpy clouds that produce weak to moderate precipitation

Examples include Nimbostratus and Stratocumulus

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Clouds: Five Types of Clouds4. Vertically developed: These clouds are thick and puffy and extend very far upwards

Examples include Cumulonimbus and Fair Weather Cumulus

Ordinary Cumulus clouds can quickly become Cumulonimbus clouds that start strong thunderstorms

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Clouds: Five Types of Clouds5. Other: These are miscellaneous clouds

These clouds do not really fit into any category, and all have different characteristics

Examples include billow clouds, contrails, mammatus, orographic, and pileus

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Weather Maps: Pressure & Temperature

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Weather Maps: Doppler Radar Maps

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Summary Temperature: Usually in °F, need to convert to °C

High pressure areas cause sunny weather; low pressure areas cause rain and storms

Two Types of air masses:

1. Continental Polar

2. Maritime Tropical

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Summary (continued) Five types of fronts:

1. Cold2. Warm3. Stationary4. Occluded5. Dew Point (Dry Line)

Five types of clouds:1. High Level2. Mid Level3. Low Level4. Vertically developed5. Miscellaneous

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SourcesPalmer, Chad and Evans, David. May 20, 2005. Occluded fronts can

signal weakening of storm. Accessed 28 October 2005. http://www.usatoday.com/weather/tg/wofront/wofront.htm

Palmer, Chad and Kepple, Kevin. May 20, 2005. High-pressure systems

brings sunny days. Accessed 27 October 2005.http://www.usatoday.com/weather/tg/whighp/whighp.htm

Palmer, Chad and Kepple, Kevin. May 20, 2005. How low pressure systems affect weather. Accessed 27 October 2005.

http://www.usatoday.com/weather/tg/wlowpres/wlowpres.htm

Weather World 2010, University of Illinois. No date of publicationgiven. Reading and Interpreting Weather Maps. Accessed

21 October 2005. http://ww2010.atmos.uiuc.edu/(Gh)/guides/maps/home.rxml