GEOG 131 Lab 10 - Mid-latitude cyclones

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Geography

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Dec 6, 2023

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1 Name: Lab Day and Time: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ LAB 10: WEATHER MAPS AND MID-LATITUDE CYCLONES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ LEARNING OBJECTIVES This lab focuses on weather maps, mid-latitude cyclones, and weather forecasting. By the end of this week's lab, you will be able to: • Read and interpret weather maps. • Apply weather forecasting techniques. • Describe midlatitude cyclone development. • Distinguish between the influences of different air masses using weather conditions as clues. See the reference sheet on the last page. It will help! ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ This exercise will give you experience with interpreting weather maps and using them to make weather forecasts. It includes a sequence of five daily weather maps covering the conterminous U.S. for March 11 – 15, 1993. Each map represents the situation at 7:00 AM Eastern Standard Time on the date given. These maps are from the “ Daily Weather Maps ” series published by the National Oceanic and Atmospheric Administration and the National Weather Service. The large map at the top of each page shows several types of information. Surface barometric pressure is represented by isobars spaced at 4 mb intervals. High- and low-pressure centers are marked and their associated cold, warm, stationary, and occluded fronts are represented by the thick dashed or decorated lines. The small black boxes that contain a white X represent the position of the center of a low-pressure system 6, 12, 18, and 24 hours prior to the time the map was drawn (7:00 AM). The groups of small numbers surrounding a small circular symbol represent the data gathered at individual weather stations (see keys on pages 8-9). Areas of precipitation are indicated by shading. Areas that dipped below 32° F on the previous day are outlined by a thin dashed line. Areas that went below 0° F are surrounded by a thin dash/dot line. The map at the lower left of each page shows contour lines that represent the height above the surface at which barometric pressure reaches 500 mb. These heights are measured in decameters (1 decameter = 10 meters) and the contour interval is 6 decameters. High- and low-pressure centers aloft are labeled. The “arrows” are shown as flying with the upper -level wind and the wind speed is indicated by the number of attached flags and barbs. Isotherms (the thin dashed lines) represent the temperature in degrees Celsius at the 500 mb level. The small map at the right center represents the maximum and minimum temperatures at weather stations for the previous day. Maximums are taken from the 7 AM to 7 PM period while minimums are taken between 7 PM and 7 AM. The map at the bottom right represents precipitation amounts and areas for the past 24 hours. Trace amounts of precipitation are represented by the abbreviation “ T. ” The shaded areas have received some form of precipitation

2 and the amount is given to the nearest hundredth of an inch (snow is converted to depth of liquid water for this). The dashed lines represent the depth of snow on the ground at 7:00 AM. The plastic models of midlatitude cyclones will help you visualize the Storm of the Century in three dimensions. Look at one as you work through the activities. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ MAP FOR THURSDAY, MARCH 11 On this map, the low-pressure center that later developed into the Storm of the Century is not yet visible. In the past 24 hours, a cyclonic storm moved out into the Atlantic while a moderately strong high-pressure system has moved south from central Canada into the northern Plains states. 1. Although the Storm of the Century low-pressure center is not yet visible, there are a few subtle hints that one might be starting to form around Brownsville, Corpus Christi, and Laredo, TX. What do the surface wind patterns appear to indicate in this vicinity? 2. Locate the weather station data for Knoxville and list the conditions for 7 AM. • Temperature: Dew point temperature: • Cloud cover: Pressure change and trend: • Wind direction: Present weather: 3. Has there been any precipitation in Knoxville in the last 24 hours? If so, how much? a. Has Chattanooga received any precipitation? If so, how much? 4. Find the weather stations in Mobile, AL and Tampa, FL. Using data for temperature and dew point given at these stations, roughly compare the relative humidity in these two locations. Which is higher? a. Explain why two cities located on the Gulf of Mexico would have such different relative humidity values. Hint: think about air masses. MAP FOR FRIDAY, MARCH 12 By 7 AM on March 12, the surface low to the east of Brownsville, TX has become well developed (isobars have begun to close around the low-pressure center and there are cold and warm fronts forming). Because of the initial location of this cyclone and the process by which it was formed, it is termed a West Texas Gulf Cyclone. Some other low-pressure systems are

3 named for the areas in which they form, for example: Alberta Clippers (one caused temperatures in Knoxville to plummet to – 24° F in January of 1985), Colorado Lows, and New Mexico Lows. 1. Locate the weather station data for Knoxville and list the conditions for 7 AM. • Temperature: Dew point temperature: • Cloud cover: Pressure change and trend: • Wind direction: Present weather: 2. Has there been any precipitation in Knoxville in the last 24 hours? If so, how much? 3. Look at the surface wind speeds and directions at the weather stations surrounding the low- pressure center. What clear pattern emerges about surface wind flow around the low? a. At which station near the low do you find the strongest winds? b. Why are these strong winds found in this location (what feature of the cyclonic storm are they associated with)? 4. Understanding that the direction of motion of a mid-latitude cyclone can often be predicted by the location of the most rapidly falling pressures (low will move towards area of falling pressure), in what direction would you expect the storm center to move? a. Which direction will the storm center move? b. Which direction will the warm front move? c. Which direction will the cold front move? MAP FOR SATURDAY, MARCH 13 1. In what direction has the storm center moved in the past 24 hours? a. Does this agree with your prediction? Why or why not?

4 b. How fast has the center moved in Nautical MPH? (Use the distance scale for 30° N) 2. Where is the cold front located? a. How have wind speeds and directions at the weather stations in Florida been affected by the passing of this front? b. The linear feature located to the east of the cold front is called a squall line. What is happening there? 3. Locate the weather station data for Knoxville and list the conditions for 7 AM. • Temperature: Dew point temperature: • Cloud cover: Pressure change and trend: • Wind direction: Present weather: 4. Has there been any precipitation in Knoxville in the last 24 hours? If so, how much? Notice the symbols for both snow and a thunderstorm that are listed for the Knoxville station. This is an unusual situation, which is also one of Weather Channel meteorologist Jim Cantore’s favorite weather phenomena , called thundersnow . 5. Locate the weather station for Jackson, MS and list the conditions for 7 AM. • Temperature: Dew point temperature: • Cloud cover: Pressure change and trend: • Wind direction: Present weather: 6. Locate the weather station data for Charleston, SC and list the conditions for 7 AM. • Temperature: Dew point temperature: • Cloud cover: Pressure change and trend: • Wind direction: Present weather:

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