Weather Map Worksheet
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Lee University *
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Course
122
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Geography
Date
Dec 6, 2023
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GSCI-122 OL – Weather Maps
(rev. 10/07/21)
1
Weather Maps
INTRODUCTION
Air masses are large bodies of air that take on the characteristics of the area in which they
originate. Air masses originating over Canada are cold and dry, whereas air masses originating
over the Gulf of Mexico are warm and humid. An air mass is fairly homogeneous in temperature
and pressure across its expanse, but it shows considerable vertical variation. In general, the
pressure and temperature of an air mass decrease with increasing elevation. Because of unequal
heat received by Earth’s surface from the Sun, the temperature changes; the density of the air is
thereby caused to change, and thus the pressure. Such changes coupled with Earth’s rotation bring
about movement of the air masses over the surface of Earth.
The boundary between two air
masses is called a front. If a cold air mass is moving into a warm area, the front is labeled a cold
front. If warm air is moving into a cold region, the front is called a warm front. The term weather
refers to the day-to-day variations in the general physical properties of the lower part of the
atmosphere, known as the troposphere this region varies from 7 to 11 miles in height. The physical
properties that play an active role in our daily lives are temperature, pressure, humidity,
precipitation, wind, and extent of cloud formation.
The U.S. National Weather Service is the federal organization that provides national weather
information. It is part of the National Oceanic and Atmospheric Administration (NOAA—
pronounced “Noah”), which was created within the U.S. Department of Commerce in 1970.
Under NOAA, the National Weather Service reports the weather of the United States and its
possessions, provides weather forecasts to the general public, issues warnings against tornadoes,
hurricanes, floods, other weather hazards, and records the climate of the United States.
To help analyze the data taken at the various weather stations, maps and charts are prepared
that display the weather picture. A weather Map taken on Thursday, February 19, 2004 shows
some of the important symbols used to represent the weather in these charts. Since these charts
present a synopsis of the weather data, they are referred to as synoptic weather charts. There are a
great variety of weather maps with various presentations. However, the most common are the
daily weather maps issued by the U.S. National Weather Service. A set consists of a surface
weather map, a 500-millibar height contour map, a map of the highest and lowest temperatures,
and one showing the precipitation areas and amounts.
The Surface Weather map presents station data and analysis for 7 A.M. EST for a particular
day. This map shows the major frontal systems and the high- and low-pressure areas at the
constant surface level.
1.
ISOBARS. Every weather map is marked by a series of either closed or endless “contour”
lines called isobars. Each Isobar connects points of equal atmospheric pressure. Notice the
small numbers such as 1008, 1012, 1016, 1020, etc., on the isobars of figures. These
numbers represent a measurement of the atmospheric pressure in millibars. Standard
GSCI-122 OL – Weather Maps
(rev. 10/07/21)
2
Atmospheric Pressure as measured by the barometer is either 760 millimeters or 30 (29.
921) Inches of mercury. Either of these units is equivalent to 1013.25 millibars.
2.
Barometric Pressure on station models.
Barometric pressures can vary and sea-level
ranges can be from 960.0 to 1040.0.
(The lowest recorded is 870.0 inside a hurricane and
1080.0 in the Siberian desert.)
As a space saving tool the barometric pressure is recorded
as three digits on station models indicating the last two digits and the decimal (without the
decimal).
Thus, 960.5 would be indicated as 605 and 1040.2 would be indicated as 402.
In general if the pressure is 501 or higher you would place a 9 in front to convert it back
into millibars.
(ex.
678 would be 967.8 mb). If the value is 499 or lower, you would place
a 10 in front of the number.
(ex. 213 would be converted to 1021.3 mb)
3.
HIGHS and LOWS. By using the Isobars one is able to determine those geographical areas
affected by atmospheric pressure “higher” or “lower” than the standard or normal pressure
of 1013 millibars.
4.
FRONTS. The boundary between two different air masses is called a front. There are four
different kinds of fronts and each is represented by different symbolism. A cold front is the
boundary of relatively cold air of polar origin advancing into an area occupied by warmer
air. A warm front is the boundary of relatively warm air advancing into an area occupied
by colder air. An occluded front is the line along which a cold front has overtaken a warm
front at the ground. A stationary front is the boundary between two air masses, neither of
which shows a tendency at the time of observation to advance into either the warm or the
cold area. Front symbols are given below. The side of the line on which the symbols are
placed indicates the direction of movement
The most outstanding features shown on a daily weather map (see Experiment 3) are the warm
and cold fronts.
In addition to the long black lines with their rounded or sharp-pointed projections that
symbolize a warm or cold front, there are plain dark lines with open ends, and others that form
complete circles. These lines, called isobars, are lines of equal pressure, and their central areas
indicate regions of high or low pressure.
A study of the weather map will show many facts concerning the weather elements associated
with these pressure cells. The first noticeable feature is the way the isobars are plotted on the map.
Note the unit of measurement and the difference between any two isobars drawn on the map. It is
clearly seen that reporting stations seldom report these particular values of pressure; the isobars
are drawn between the known values indicated at the stations.
Note how the pressure varies as one approaches the center of the high- or low-pressure cell.
Also note the fact that no two isobars ever cross. Why?
LEARNING OBJECTIVES
After completing this experiment, you should be able to do the following:
GSCI-122 OL – Weather Maps
(rev. 10/07/21)
3
1.
Define air mass, warm front, cold front, isobar, isotherm, and wind.
2.
Read weather information from surface weather maps issued by the National Weather
Service.
3.
Plot station reports similar to those found on Surface Weather maps.
4.
Define high-pressure cell, low-pressure cell, and isobars.
5.
Identify and explain the physical characteristics of weather associated with high-pressure
and low-pressure cells.
6.
Plot pressure values on a map and draw lines of equal pressures (isobars) on the map.
APPARATUS
This Laboratory Guide and daily weather maps (weekly series) from the National Weather
Service.
PROCEDURE: Part 1
Please watch the video
How to... Read and interpret pressure on a weather model.
Using
Table 1 and Figure 1 for reference, create a station model form the information given below for
the three cities (A, B, and C).
Please refer to the introduction item 2 to ensure you record the
pressure correctly.
City A
City B
City C
Air temperature
62°F
88°F
32°F
Air dew point
60°F
52°F
26°F
Air pressure
1022.6 mb
987.4 mb
1042.8 mb
Wind direction
SW
NW
Wind magnitude
24 knots
Calm
10 knots
Cloud coverage
0.75
No clouds
0.5
Present weather
Continuous rain
Intermittent fall of
snowflakes,
moderate
City A
City B
City C
62
60
62
.
.
.
·
d
226
88
874
*
428
52
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GSCI-122 OL – Weather Maps
(rev. 10/07/21)
4
Selected Weather Symbols
Table 1 – Selected Weather Symbols
GSCI-122 OL – Weather Maps
(rev. 10/07/21)
5
Figure 1 – Specimen Station Model
GSCI-122 OL – Weather Maps
(rev. 10/07/21)
6
1.
Using Table 1 and Figure 1 for reference, record the information request for each city
listed.
Please evaluate (think about) the four weather conditions that are described by the
station model.
Indicate if the model makes sense (Y) or doesn’t make sense (N) based on
the described weather condition?
Temperature,
in degrees ºF
Dew point, in
degrees ºF
Barometric
pressure, in
millibars
Wind
direction
Wind
magnitude, in
knots
Condition
likely?, Y/N
72
39
⊥
le
19
63
35
58
17
1004
.
6
1032
.
0
999
.
4
1000
.
O
S
NW
Calm
NE
25
S
Calm
30
Y
Y
Y
Y
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GSCI-122 OL – Weather Maps
(rev. 10/07/21)
7
Using the weather map in Fig 2 below,
Figure 2 – Warm and Cold Front
2.
Determine and record the temperature ahead or behind both a cold front and a warm front.
Indicate whether the temperature rises or falls as the front is move into a city.
Cold front
Warm front
Temperature ahead
Temperature behind
Rise or fall
3.
Record the barometric pressure that exists on either side of the fronts and indicate whether
they rise or fall as the front is crossed into a city. Use the isobars to determine the pressure
for each station model.
If a city is not directly on a line you must estimate the pressure in
millbars
Cold front
Warm front
Pressure ahead
Pressure behind
Rise or fall
48
25
rise
44
20
fall
Fall
rise
GSCI-122 OL – Weather Maps
(rev. 10/07/21)
8
PROCEDURE: Part 2
1.
A high-pressure area is shown (Fig 3). For each station model I want you to evaluate I have
created a box.
In that box I want you to describe two items 1. draw an arrow for the wind
direction indicated on the station model and 2. indicate the direction of the wind.
The station
model that must be evaluated is indicated by the arrow pointing to the model and the box.
In the bottom right, I have an arrow pointing to a station model that has a temperature of 20
F
and a dew point of 16
F.
I have drawn an arrow indicating the wind direction that is shown on
the station model and have indicated the wind direction as the wind is come from the E.
Fig 3
clockwise or
counterclockwise?
sw
->
West
s
-
NE
-
O
GSCI-122 OL – Weather Maps
(rev. 10/07/21)
9
2.
A low-pressure area is shown (Fig 4). For each station model I want you to evaluate I have
created a box.
In that box I want you to describe two items 1. draw an arrow for the wind
direction indicated on the station model and 2. indicate the direction of the wind.
The station
model that must be evaluated is indicated by the arrow pointing to the model and the box.
In the bottom right, I have an arrow pointing to a station model that has a temperature of 36
F
and a dew point of 32
F.
I have drawn an arrow indicating the wind direction that is shown on
the station model and have indicated the wind direction as the wind is come from the WSW.
A low-pressure area is shown. Draw an arrow and indicate the direction of the wind.
Fig 4
clockwise or
counterclockwise?
NE
NW
SE
-
S1
-
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GSCI-122 OL – Weather Maps
(rev. 10/07/21)
10
3.
Record the maximum pressure indicated on any isobar shown on the weather map dated Thursday, February 19, 2004.
4.
Record the minimum pressure indicated on any isobar shown on the weather map dated Thursday, February 19, 2004.
Fig 5
1024
994
GSCI-122 OL – Weather Maps
(rev. 10/07/21)
11
Draw in the 1016, 1020, and 1024 isobars.
Fig 6
17.9
19.6
16.8
18.1
20.2
16.8
15.2
23.4
19.6
18.2
18.9
21.8
23.7
25.7
24.5
25.7
26.1
24.5
24.3
20.7
19.4
19.8
20.6
18.7
18.7
20.7
22
16.8
17.3
14
15.8
14.1
17.1
20.1
20.1
19.1
22.4
24.5
-
n
GSCI-122 OL – Weather Maps
(rev. 10/07/21)
12
QUESTIONS
1.
List the changes in the temperature and the air pressure that occur as a warm front
passes over a surface area.
2.
List the changes in the temperature and the air pressure that occur as a cold front
passes over a surface area.
3.
The Surface Weather map (Fig 5) presents data and analysis for what time of day?
4.
Define an isobar. How are they represented on the weather map?
5.
Define an isotherm. How are they represented on the weather map?
6.
How is the amount of precipitation indicated on the weather map?
7.
What is the usual range of atmospheric pressure (in millibars) at Earth’s surface?
increase
in
temperature
decrease
in
temperature
7
:
00
AM
Points
that
connect
same
man
sea
level
air
pressure
.
Plain
lines
that
curve
on
map
.
Line
drawn
on
map
that
join
points
w/
save
temperature
,
Color
960
.
0-1040
.
0
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GSCI-122 OL – Weather Maps
(rev. 10/07/21)
13
8.
What is the difference in pressure, in millibars, indicated by two adjacent isobars?
9.
What is the direction of the air circulation around a low-pressure cell in the northern
hemisphere?
10.
What kind of weather is usually associated with a low-pressure cell in North
America?
11.
What is the direction of the air circulation around a high-pressure cell in the northern
hemisphere?
12.
What kind of weather is usually associated with a high-pressure cell?
13.
A pressure of 1012 mb is indicated on a weather map. Is this pressure high or low?
Explain.
760mil
.
anticlockwise
direction
.
inclement
weather
clockwise
direction
.
dry
weather
and
clear
skies
.
High
Pressure