1. Weather Lesson

2. 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

3. Weather Instruments
(click below the picture)
http://www.weatherwizkids.com/weather-instruments.htm

4. 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)

6. 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

7. We ALWAYS go HIGH  LOW

8. 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).

9. Local Winds
Sea 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

10. 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.

12. Fronts
Front: a boundary between Air Masses
• Four Types of Fronts:
1. Cold
2. Warm
3. Occluded
4. 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.

14. Station Models
Station 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.

15. How to Draw Isolines
(lines of equal value on a map)
Click on the Picture

16. 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.