Lab 8_Meteorology_edited_3_15_20 (1)
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Feb 20, 2024
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Lab 8 – Meteorology Name Objectives
Understand air pressure and the change in pressure with height.
Learn how to draw isotherms on a surface weather map.
Learn the components of a station plot and how they are used on a surface weather map.
1.
Surface Air Pressure
This map shows the sea level pressures for various locations over the contiguous U.S. The values are in whole millibars.
Using a dark pencil or pen, 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.
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Procedure
Begin drawing from the 1024 millibars station pressure over Salt Lake City, Utah (highlighted in blue). 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 and then to the one located southwest, finally returning to the Salt Lake City value. Remember, isobars are smooth lines with few, if any, kinks.
The result is an elongated circle, centered approximately over Eastern Utah. The line that was drawn represents the 1024 millibars line and you can expect the pressure to be 1024 millibars everywhere along that line. Repeat the procedure with the next isobar value. Remember, the value between isobars is 4 millibars. Since there are no 1028 millibars values on the map, then your next line will follow the 1020 millibars reports. Then continue with the remaining values until you have all the reports connected with an isobar.
Label each isobar with the appropriate value. Traditionally, only the last two digits are used for labels. For example, the label on the 1024 mb isobar would be 24. A 1008 mb isobar would be labeled 08. A 992 mb isobar will be labeled 92. These labels can be placed anywhere along the isobar but are typically placed around edges of the map at the end of each line. For closed isobars (lines that connect) a gap is placed in the isobar with the value inserted in the gap.
Analysis
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 "
H
".
Label the center of the low pressure area with a large "
L
". 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.
Lightly shade the state(s) would you expect to see rain or snow.
Do not shade the state(s) would you expect to see clear skies.
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. 2.
Surface Air Temperature
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This map shows the air temperature for various locations over the conterminous U.S. The values are in °F.
Objective
Using a pencil, lightly draw lines connecting equal values of temperatures, every 10°F. Remember, like isobars, these lines (called isotherms) are smooth and do not cross each other.
Procedure
You will draw lines connecting the temperatures, much like you did with the sea-level pressure map. However, you will also need to interpolate
between values. Interpolation involves estimating values between stations which will enable you to properly analyze a map.
We will begin drawing from the 40°F temperature in Seattle, Washington (top left value). Since we want to connect all the 40°F temperatures together, the nearest 40°F value is located in Reno, Nevada, (southeast of Seattle). However, in order to get there you must draw a line between
a 50°F temperature along the Oregon coast and a 30°F temperature in Idaho. Since 40°F is halfway between the two locations, your line from Seattle should pass halfway between the 50°F and 30°F temperatures.
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3.
Station Plots – Surface Weather Map
Television weather reports represent weather conditions with smiling suns, rainy clouds and flashing bolts of lightning. In studying the weather we need to know where it is raining and where it is sunny, the wind speed and direction, humidity, visibility, pressure and temperature. To understand the weather we need to know how these meteorological
variables are changing and how they relate to one another. To understand these relationships it is best to represent weather variables in a simple graph. Smiling suns do not contain enough information about the weather. On the other hand too many numbers drawn on a single map presents a confusing picture. Weather conditions observed at a city or town are best represented on a map using the station model.
Sample Station Front
i.
Using the weather map symbol guide at the end of this lab,
draw the appropriate symbols for the weather conditions given.
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Air temperature
: 72 F
Dew point
: 71 F
Air pressure
: 1018 mb
State of the sky (sky coverage)
: 8/8
th
or Overcast
Weather type
: Thunderstorm, heavy, with hail at time of observation
Wind direction
: South-east
Wind speed
: 15 knots
ii.
Decoding Station Plots:
This is an example of a surface station plot for Detroit, Michigan. Based on your understanding from weather symbols (provided on the end of assignment), answer the following questions:
a)
What is the dew point temperature at Detroit?
48
b)
What is the temperature?
5
55
c)
What is the wind direction (N, S, E, W)?
W
d)
What is the wind speed?
20 knots
e)
What type of cloud cover is Detroit experiencing?
No clouds
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