4DA-03PA COOPERATIVE EXTENSION SERVICE UNIVERSITY OF KENTUCKY—COLLEGE OF AGRICULTURE Weather Variables Kentucky 4-H Weather Project Unit III Tom Priddy, Extension Agricultural Meteorologist AGRICULTURE & NATURAL RESOURCES • FAMILY & CONSUMER SCIENCES 4-H/YOUTH DEVELOPMENT • COMMUNITY & ECONOMIC DEVELOPMENT Weather Variables Introduction In this unit of the 4-H weather Contents project, we will be looking at and de- Introduction .................................................................................................. 2 scribing how to measure the Objectives .................................................................................................... 2 different elements that make the Activities ....................................................................................................... 2 weather. These elements, such as air temperature, wind speed and direc- Temperature tion, and precipitation, are normally Why Kentucky Temperatures Vary ................................................................ 3 called the weather variables because Activity: Making an Accurate Rain Gauge .................................................... 3 each element changes with time, yet are all related. We’ll look at these re- Winds lationships and forecasting in detail in Making a Weather Vane ............................................................................... 4 Unit IV. Thar’ She Blows ........................................................................................... 4 First, let’s learn about temperature Where the Winds Come From ...................................................................... 4 as a weather variable. Why Our Winds Blow from West to East ...................................................... 5 Kentucky Breezes and Winds ....................................................................... 6 Objectives How Fast Is the Wind Blowing ...................................................................... 6 • Learn how temperature changes Experiment: Making a Cup Anemometer ...................................................... 6 affect other weather conditions. The Beaufort Scale for Measuring Wind Speed ........................................... 7 • Learn how wind patterns affect the weather. Humidity • Learn why humidity is one of the Understanding Water Vapor in the Atmosphere ........................................... 8 weather variables. 100% Relative Humidity or Saturated Air? ................................................... 8 The Hair Hygrometer .................................................................................... 8 Building a Hair Hygrometer .......................................................................... 9 Activities • Make a weather station. Summing Up • Give a weather demonstration. What’s Next? ................................................................................................ 9 • Exhibit a weather station at the Talks & Demonstrations................................................................................ 9 county fair. Citizenship & Leadership Activities .............................................................. 9 • Submit project records and weather observations. Observation Sheets .................................................................................... 10 Weather Variables Record Sheet ............................................................... 12 2 Temperature One of the first questions we ask and the funnel, you have made a shield about the weather is, “What is the tem- that will prevent evaporation and help perature?” In Unit I, you learned how you to make more accurate readings. to keep temperature readings, and in Now, you are ready to take read- Unit II, you continued to keep those ings. Measure the precipitation with a readings. But just what do these read- plastic ruler just as you did before. Re- ings mean? Temperature affects all member to pour out the precipitation other weather conditions. Without after each reading so your next read- changes in temperature, there would ing will be accurate. (You will be keep- be no changes in pressure, wind, or ing records of the precipitation for humidity. three months.) A general rule is to For this project, you can use the measure precipitation to the nearest same thermometer you used in Units tenth of an inch. (What other units of I and II. If you need a new thermom- measure could you use? Hint: MM). eter, many feed stores and farm-re- Comparing your reading with the lated businesses give them away free, weather news will help you learn to or you may want to purchase an inex- be more accurate. You may wish to pensive one. Put the thermometer in devise a holder for your rain gauge your weather shelter where it will be and mountains. These differences in so it will not blow over. Keep your rain out of direct sunlight and yet will have the terrain can readily influence gauge on top of your weather station air circulating around it. weather changes. The Appalachian (see Figure 1). Mountains are located in the North- east, Quicksand, and Wilderness Trail Why Kentucky areas. As weather moves from the Temperatures Vary western sections of Kentucky, the air must rise to travel across the moun- Have you ever participated in tains. As the air attains a higher alti- 4-H events with 4-H’ers from a tude, the temperatures cool. Not only different part of the state? In Kentucky, does this produce a temperature 4-H’ers compete on local, county, area, change but also helps to create rainfall. and state levels. Perhaps when you went to 4-H camp or attended Ken- tucky 4-H Week in Lexington, you had Activity: Making an the opportunity to talk to members funnel from many different 4-H areas. Did Accurate Rain you know that their weather may dif- Gauge candle wax fer from yours? Watch the TV weather In Unit II you learned how to use a brief for one week and record the daily simple rain gauge. For this unit, you will high temperature near your location improve your rain gauge to make it and one other location across the more accurate. First, check your old rain plastic disc state. Discuss these differences in the gauge. Make sure the paint has not temperature readings. One reason chipped and the can will not rust. Sec- temperature varies throughout Ken- ondly, cut a circle of plastic foam that tucky is that our latitude varies. The far- will fit inside the can snugly. Now, ther one travels north, the cooler the make a hole in the middle of the plas- tin can temperature will be. tic large enough for the end of the fun- Another major reason for air tem- nel to be placed. The funnel must be perature differences in Kentucky is the the same diameter (distance across wide variety of terrains. In the Blue the top) as the can. Why is this so? Grass and Fort Harrod areas, the land (Hint: Compare the area of the top of is fairly flat. In comparison, the east- the funnel to that of the can.) Put the ern portion of the state has many hills funnel in place. By adding the plastic Figure 1. Advanced rain gauge. 3 Winds Long before weather vanes or wind-measuring instruments had been thought of, early weather watch- ers recognized that wind direction was important. They didn’t understand why, but they knew that wind from one direction generally brought fair skies while wind from another direction brought rain. So they watched the trees sway for a sign of the wind direction. Making a Weather Vane Today we have better ways of de- termining wind direction. A sensitive Figure 2. Weather vane. weather vane can be constructed fairly easily. You will need a piece of wood for an arrow about 12" long, ½" • Winds from the west, southwest, stant heat forms a low pressure belt thick, and 3" wide; a mounting stick; a and south bring fair and warmer of rising air known as the Doldrums. ¾" by 1' board; a nail or screw for at- weather. They blow from warmer According to Figure 3, as air rises taching the arrow to the mounting lands. from the Doldrums, it cools and drifts stick; and two washers (see Figure 2). • Winds from the east, southeast, toward the poles. Some of it falls in the Draw an arrow like the one shown. and northeast generally bring Horse Latitudes, around the 30° lati- Then, cut the arrow out of the wood. rain. They blow in from the ocean. tude, and piles up to create a belt of You may ask your leader to supervise. In Kentucky, the most common high pressure. The constant pressure Find the point where the arrow is wind direction is from the south. How- of the Doldrums and the Horse Lati- equally balanced by steadying it on ever, during February and March, tudes makes these regions of calm or your finger. This is the balance point. northwesterly winds are common. For very light winds. But in between them, Drill a hole at that point through the the next three months, you will be re- air is on the move. Rushing from high shaft of the arrow. Paint the weather cording the wind direction. pressure to low pressure, the air flows vane white to match your weather sta- back toward the equator as the strong tion. Now, you are ready to attach the Where the Winds and steady northeasterly Trade Winds. weather vane to your weather station. Some of the air that rises from the Be sure one side of the mounting stick Come From equator continues on to the poles. faces north. Label the stick with the Wind is caused by air moving from There it sinks, becomes compressed, compass points—north, east, south, a high pressure to a low pressure area. and rushes out toward the 60° latitude. and west—ensuring