Name _________________________
Lab 3: Drawing Isopleths: Isobars vs. Surface Weather Maps
Factoid...We often speak of pressure in terms of atmospheres. One atmosphere is equal to the weight of
the earth's atmosphere at sea level, about 14.7 pounds per square inch. If you are at sea level, each square
inch of your surface is subjected to a force of 14.7 pounds. Maps depicting weather and ocean conditions
are drawn based on simultaneous observations made at many places throughout the world. Accurate
portrayal of these observations is the key to a correct interpretation of the data. Meteorologists and
oceanographers use a technique called contour analysis to visually explain the information the data is
providing. Ability to correctly and confidently analyze data is critical to interpreting conditions.
In water, the pressure increases about one atmosphere (14.7 pounds per square inch) for every 33 feet (10
meters) of water depth. At the deepest part of all the earth's oceans, Marianas Trench's (east of the
Philippine Islands) depth is about 35,800 feet (7 miles/11 km). The pressure of nearly 7 miles of water
overhead is about 1080 atmospheres or 16,000 pound per square inch.
Normal sea-level pressure = 14.7 lbs./in2 = 1013.2 mb = 760 torr = 29.92 in Hg Draw lines of equal
concentration.
In this lab, you will build on Lab 2 and plot isobars (lines of equal pressure) for various maps provided.
If necessary, go to Lab 2 for a review on contouring. In addition, the last map will include station models
across the Southeastern United States. Refer to the PowerPoint for rules on decoding station models.
More information on surface weather plot symbols can be found here.
To complete this lab, analyze the following data fields as instructed, sign and turn in.
Map 1: This map is composed of pressure observations (millibars) across the eastern half of the
United States. Lines of equal pressure are called “isobars”. In the map below, draw isobars for the
values of 1000, 1004, 1008, 1012, 1016, 1020, and 1024.
Map 2: In the map below, draw isobars for the values of 1016, 1020, 1024, and 1028.
Question 3: Decode the following station models.
KBWG
Temp:
Dewpoint:
Precip:
Pressure:
Wind Direction:
Wind Speed:
Cloud Cover:
KORT
Temp:
Dewpoint:
Precip:
Pressure:
Wind Direction:
Wind Speed:
Cloud Cover:
Question 4: Draw station models based on the following data.
KABR
Temp:
Dewpoint:
Precip:
Pressure:
Wind Direction:
Wind Speed:
Cloud Cover:
Map 5: Analyze the map below in intervals of 4 mb’s from 1004 mb to 1020 mb. Notice that station
models will have to be decoded to complete.