Weather Lesson

Objectives

• Learn about Weather Instruments• Learn about Highs and Lows• Learn about Winds Global and Local• Learn about Air Masses• Learn about Fronts• Learn how to Read and Draw Station Models• Learn how to draw isolines (lines of equal value on

maps)• Learn about Severe Weather and Clouds

Weather Instruments(click below the picture)

http://www.weatherwizkids.com/weather-instruments.htm

High and Low Pressures• Barometric (Air) pressure is the weight of the air above you. It is measured with

a barometer. Isobars are lines of equal pressure used on a weather map to show air pressure. The unit for isobars is millibars (mb).

Two Types of Pressure:• Low (L): also called a Cyclone

– Air rises in a low as winds converge at the surface– The air cools as it rises and creates clouds that can produce precipitation

• High (H): also called an Anticyclone– Air sinks and diverges away from a central point at the surface– The air warms as it subsides (goes down) which doesn’t allow for cloud formation (clear skies

are present)

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&docid=YsnwAbl9Nl4c6M&tbnid=4JX2lUDZ2BaPzM:&ved=0CAUQjRw&url=http://www.revisionworld.com/a2-level-level-revision/geography/challenge-atmosphere/weather-systems/britain-western-europe%E2%80%99s-weather-and-climate&ei=RI1iU4OsCsfJ8wGk9ID4BQ&bvm=bv.65788261,d.b2U&psig=AFQjCNFtgnHtRK_XqA5VqQ8UeDMkQdjYKw&ust=1399052272531088

Highs and Lows

Northern Hemisphere• Low (L) spins

counter clockwise• High (H) spins

clockwise

Southern Hemisphere• Low (L) spins

clockwise• High (H) spins

counter clockwise

What Causes the spin (deflection) which is named the Coriolis Effect?

Answer: Earth’s Rotation

We ALWAYS go HIGH LOW

Winds(are always named based on where they are coming from NOT where they are going to)

Example: A North wind is coming from the North BUT is heading South

Global• We live in the Prevailing

Westerlies

Local

• Sea Breezes and Land Breezes

• Valley Breezes and Mountain Breezes

• Local breezes are caused by differences in specific heat capacity of different materials (i.e., how quickly or slowly a substance absorbs heat and holds onto it).

Local WindsSea Breeze• During the day, land heats up quickly and

generates a Low pressure center where the warm air begins to rise. As the warm air rises the cooler air from the sea moves in to fill the space and creates a breeze from the sea Sea Breeze

Land Breeze• During the evening as the sun goes down

the land that heated quickly is now going to cool quickly and become cooler than the water temperature. When that happens, the low pressure is now over the water and the higher pressure from the cooler land fills in the space from the rising warmer air over the ocean creating a breeze from the land Land Breeze

Air Masses

Air Mass: a body of air with similar temperature, pressure, and humidity.• Terms for Air Masses:

– Maritime (m) related to the water, so moist air– Continental (c) related to land, so dry air– Arctic (A) related to really, really, really cold air– Polar (P) related to really cold air– Tropical (T) related to warm air

• As indicated above, the location of origin is indicated with a lowercase letter and the temperature of the air mass is indicated with an uppercase letter.

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&docid=lEP36ZmaVQOuMM&tbnid=P6Eu16l-1j1vNM:&ved=0CAUQjRw&url=http://earth.usc.edu/~stott/Catalina/WeatherPatterns.html&ei=2pJiU_6sHqmL8AGs8IGgBw&psig=AFQjCNGbyfHmaa9jkg7n7PqZbr5OeScL0g&ust=1399055334882332

FrontsFront: a boundary between Air Masses• Four Types of Fronts:1. Cold2. Warm3. Occluded4. Stationary• Fronts occur when two different air masses meet.

Very violent weather systems can and are formed when two different air masses meet.

• Violent storms include: Severe Thunderstorms and Tornadoes.

Station ModelsStation Model (SM): symbol on a weather map that describes the weather of a particular area using symbols.• Pressure on a station model is always

ONLY 3 digits. So, a conversion must be done when placing the number on and then reversing that process when taking from station model.– 1013.2 mb on SM would be 132

• Remove decimal and get rid of the 10– 999.5 mb on SM would be 995

• Remove decimal and get rid of the 9– 124 on SM would be 1012.4 mb

• Add decimal between last two digits and add a 10 if the first digit is <5

– 895 on SM would be 989.5 mb• Add decimal between last two digits

and add a 9 if the first digit is >5.• Click on the picture to the right to practice

reading station models.

How to Draw Isolines(lines of equal value on a map)

Click on the Picture

Severe Weather and Clouds(click on each picture to learn about the different types)

Make sure to take notes and write down the features of each.