7yr 09 #16 Weather Temperature

Weather!Weather!

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

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

Relative HumidityRelative 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.

Cloud Cover SymbolsCloud Cover Symbols

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

High and Low Pressure High and Low Pressure AreasAreas

• High pressure High pressure causes air to sinkcauses air to sink

• Usually results Usually results in several days of in several days of clear sunny skiesclear sunny skies

• Air rises in low Air rises in low pressure areas pressure areas and forms water and forms water dropletsdroplets

• Usually results Usually results in rain and in rain and stormsstorms

Air MassesAir MassesThere are two types of air masses:

2. Maritime Tropical air masses

1. Continental Polar air masses

1. Continental Polar air messes

Fronts

A front is the boundary separating air masses of different densities

Fronts extend both vertically and horizontally in the atmosphere

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

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

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

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

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.

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

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

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

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

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

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

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

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