LAB EXERCISE: Weather Maps
1. Draw and label the current conditions for the cities of San Diego, California, and Key West, Florida, on their weather stations on Figure 14.3. The conditions in San Diego, California, are: 1019 mb, wind 5 kts from the south; state of the sky is no clouds; temperature is 48°F, dew-point temperature is 48°F. The conditions in Key West, Florida, are: 1023 mb, wind 15 kts from the east; state of the sky is 4/Bths sky- cover; temperature is 70°F, dew-point temperature is 55°F.
2. On the weather map, draw in the isobars connecting points of equal barometric pressure, at 4-mb intervals. Each circle on the map represents a weather station. The number to the upper right of the station is the barometric pressure, rounded to the nearest whole millibar.
a) The 996-mb and 1000-mb isobars around the low-pressure center are drawn for you (pressures lower than 996 go inside the isobar, higher than 996 go outside this closed isobar; pressures between 996 mb and 1000 mb fall between the two isobars).
b) Now draw in order of increasing pressure the rest of the isobars at 4-mb intervals: 1004, 1008, 1012, 1016, 1020, 1024, and 1028. The highest-value isobar of 1032 millibars is drawn for you.
Note that the 1032-mb isobar is a closed isobar that surrounds Salmon, Idaho, which is the area of highest pressure.
Use a purple colored pencil or pen to draw an outline of the region with more than 75% sky coverage. The pattern of cloudiness is indicated by the state-of-the-sky (sky coverage) status recorded within each station symbol. The areas of frontal lifting are clearly Identified by these patterns of clouds. After completion of the isobars, determine the pattern of low-pressure and high-pressure systems on the map and related air masses to determine the position of the weather fronts. The southeastern portion of the country is influenced by a mild maritime tropical (mT) air mass. The high-pressure area around
Idaho is under the influence of a continental polar (cP) air mass.
a) Use a red colored pencil or pen and cross hatch the region that is within 600 km of the warm front or cold front and is under the mT air mass. Consider those stations with dew-point temperatures above 45° F as being under the mT air mass. Use a blue colored pencil and crosshatch the region within 600 km of the warm front or cold front and is under the cP air mass. Consider those stations with dew-point temperatures below 45° F as being under the cP air mass.
b) Use a pencil or black marker and draw big arrows indicating the general direction of the winds with: the cP air mass that is driving the cold front; the mT air mass that is driving the warm front; and the cP air mass that is in front of the warm front.
c) Locate the warm front line. The warm front has a mT air mass with winds blowing from the south on one side of it, and a cP air mass with winds blowing from the east on the other side of it. The line is drawn for you, but it lacks the red semi-circles that are the warm front symbol on maps. Use a red colored pencil or pen and draw in the red semi-circles on the side with the cP air mass.
d) Locate the cold front line. The cold front has a cP air mass with winds blowing from the north-west on one side, and a mT air mass with winds blowing from the south on the other side. The line is drawn for you, but it lacks the blue triangles of the cold front symbol on maps. Use a blue colored pencil or pen and draw in blue triangles on the side with the mT air mass.
5. On this weather map, note air temperatures in comparison with dew-point temperatures. The air temperatures and dew-point temperatures are noted to the left of each station symbol on the map.
a) List the air temperatures and dew-point temperatures for Omaha, Nebraska; Dodge City, Kansas; and Oklahoma City, Oklahoma.
b) List the air temperature and dew-point temperatures in Memphis, Tennessee; Shreveport, Louisiana; and New Orleans, Louisiana.
Recall from Lab Exercise 12 that the dew-point temperature gives you an idea of the moisture content of the cP (dry) and mT (moist) air masses, respectively.
