UNIT 2
Chapter 2: Weather Forecasting
Unit 2: Weather Dynamics
Investigating Weather Maps
Science 10
Mrs. Purba
Section 2.2
UNIT 2
Investigating Weather Maps
What can a weather map tell you?
• A lot!
• A weather map indicates
all sorts of things
to let you know the
forecast.
• It also may have some
interesting graphics
associated with it.
Section 2.2
UNIT 2
Investigating Weather Maps
Section 2.2
Weather Maps
• Weather maps simply and graphically depict meteorological
•
•
•
•
conditions in the atmosphere.
Weather maps may display only one feature of the atmosphere or
multiple features.
They can depict information from computer models or from
human observations.
On a weather map, important
meteorological conditions are plotted for
each weather station.
Meteorologists use many different
symbols as a quick and easy
way to display information on the map.
UNIT 2
Investigating Weather Maps
Understanding Symbols
Section 2.2
UNIT 2
Investigating Weather Maps
Section 2.2
Weather Maps
•
•
Once conditions have been plotted, points of equal value
can be connected by isolines.
Weather maps can have 3 types of connecting lines, or
isolines.
UNIT 2
Investigating Weather Maps
Section 2.2
Isolines
1. Lines of equal temperature are called isotherms. Isotherms
show temperature gradients and can indicate the location of a
front.
UNIT 2
Investigating Weather Maps
Section 2.2
Isolines
2. Isotachs are lines of constant wind speed. Where the minimum
values occur high in the atmosphere, tropical cyclones may
develop. The highest wind speeds can be used to locate the jet
stream.
UNIT 2
Investigating Weather Maps
Section 2.2
Isolines
3. Isobars are lines of equal average air pressure at sea level.
Closed isobars represent the locations of high and low pressure
cells.
UNIT 2
Investigating Weather Maps
Section 2.2
What is an Isobar?
• “line” showing a weather pattern
• a “line” drawn on a weather map that connects places with
•
•
•
•
equal atmospheric pressure.
Isobars are often used collectively to indicate the
movement or formation of weather systems.
Isobar lines may never cross or touch.
Isobar lines may only pass through pressures of 1000+/- 4.
In other words, allowable lines are 992, 996, 1000, 1004,
1008, and so on.
UNIT 2
Investigating Weather Maps
Section 2.2
Drawing Isobars
• You will use a black colored pencil to lightly draw lines connecting
identical values of sea level pressure.
• Remember, these lines, called isobars, do not cross each other.
• Isobars are usually drawn for every four millibars, using 1000
millibars as the starting point.
• Therefore, these lines will have values of 1000, 1004, 1008, 1012,
1016, 1020, 1024, etc., or 996, 992, 988, 984, 980, etc.
• You will then identify a high pressure center and a low pressure
center.
• You will predict the location of fair weather and stormy weather.
• You will identify the direction of spin around a high pressure center
and a low pressure center.
UNIT 2
Investigating Weather Maps
• Begin drawing from the 1024 millibars station pressure over Salt Lake
•
•
•
•
City, Utah (highlighted in gray).
Draw a line to the next 1024 value located to the northeast (upper
right).
Without lifting your pencil draw a line to the next 1024 value located to
the south, then to the one located southwest, finally returning to the
Salt Lake City value.
Now connect the pressure areas that are 1020 millibars.
Complete the map.
Section 2.2
UNIT 2
Investigating Weather Maps
Section 2.2
UNIT 2
Investigating Weather Maps
Section 2.2
Labelling Highs & Lows
•
•
•
•
•
Isobars can be used to identify "Highs" and "Lows."
The pressure in a high is greater than the surrounding air.
The pressure in a low is lower than the surrounding air.
Label the center of the high pressure area with a large blue
"H".
Label the center of the low pressure area with a large red
"L".
UNIT 2
Investigating Weather Maps
Section 2.2
UNIT 2
Investigating Weather Maps
Section 2.2
Adding Weather
•
High pressure regions are usually associated with dry
weather because as the air sinks it warms and the
moisture evaporates.
• Low pressure regions usually bring precipitation
because when the air rises it cools and the water vapor
condenses.
• Shade, in green, the state(s) where you would expect
to see rain or snow.
• Shade, in yellow, the state(s) where you would expect
to see clear skies.
UNIT 2
Investigating Weather Maps
Weather Rhyme
•
•
When pressure is low, expect rain or snow.
When pressure is high, look for a blue sky.
Section 2.2
UNIT 2
Investigating Weather Maps
Section 2.2
UNIT 2
Investigating Weather Maps
Section 2.2
UNIT 2
Investigating Weather Maps
Section 2.2
Put A Spin On It
•
•
•
•
In the northern hemisphere the wind blows clockwise
around centers of high pressure.
The wind blows counterclockwise around lows.
Draw arrows around the "H" on your map to indicate the
wind direction.
Draw arrows around the "L" on your map to indicate the
wind direction.
UNIT 2
Investigating Weather Maps
Section 2.2
UNIT 2
Investigating Weather Maps
Section 2.2
Summary
•
•
Weather maps graphically depict weather conditions.
Weather maps have 3 types of isolines (connecting lines)
1. Isotherms are lines of constant temperature.
2. Isotachs are lines of constant wind speed.
3. Isobars are lines of constant pressure.