Background Information

What clothes should I wear today? Should I walk, bike, or get a ride to school or work? Will it rain or snow, or will the sun shine? The answers to these questions, asked by young and old, depend on current and future weather conditions.

Weather also affects aviation, agriculture, fishing, shipping, and recreation. Forecasters believe that information on upper air wind speed and direction are the most important data to have when they are preparing a forecast. For example, the ability to predict wind shear and precipitation is a key element in preventing aviation disasters.

The wind profiler is a Doppler radar which measures upper level winds. It operates in nearly all weather conditions. The National Oceanic and Atmospheric Administration (NOAA) has installed a network of 32 wind profilers mostly in the central United States where much of the dangerous weather occurs. Data on wind speed and direction are gathered by each profiler every six minutes vertically up to about 50,000 feet (15 km). These data are processed and given to forecasters every hour as hourly averages.

The weather balloon, which for many decades has been used to track winds, typically gathers information only once every 12 hours. The wind profiler, with its hourly averages, provides forecasters with more accurate wind information much more frequently than the weather balloon, and may in fact replace them. Figure 2-1 shows an artistic diagram of a wind profiler site, while Figure 2-2 gives a map of the central United States with the locations of the two wind profiler sites that will be used in this activity.

Figure 2-1. A Wind Profiler Site.
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Figure 2-2. Locations of Wind Profiler Sites for Activity 2.
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Profiler data are recorded on a graph called a wind profiler plot. The wind profiler plot shows how winds change with time above a specific location on the Earth's surface.

Wind profiler plots indicate wind speed in knots and wind direction at different heights and pressures in the atmosphere. Profiler plots indicate wind speed in knots, where 1 mile per hour is equivalent to 0.8684 knots. Notice that profiler plots use UTC (Coordinated Universal Time) - also called Greenwich Mean Time (GMT) - as the time increment.

The wind profiler plot is a computer printout with flags and barbs that indicate wind direction and speed. A flsg is simply a line ( \ ). The flag can have long and short lines called barbs. These are used to indicate the wind speed for each flag. Each long barb indicates a recorded wind of 10 knots, while each short barb indicates 5 knots. An elongated triangular shaped barb indicates a recorded wind of 50 knots.

Wind is always identified by the direction from which it blows. The end of the flag attached to the barbs points to the direction the wind comes from. Refer to Figure 2-3 for examples where the wind is blowing from the southeast, where north is at the top of the diagrams.

Figure 2-3. Sample Flags and Barbs Combined to Form
the Wind Symbols Used in Wind Profiler Plots.
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A wind profiler plot is a series of wind symbols stacked one on top of another to indicate wind speed and direction at increasing altitudes. There is a stack for each hour and there are usually 12 hours on each plot.

NOTE: Figures 2-4 and 2-6 in "Procedure" give examples of wind profiler plots.

In the following procedure, you will use profiler plots to develop a general body of information about the winds at the profiler sites over time. The profiler plots included in this activity are examples of actual wind data used by meteorologists and researchers at the National Oceanic and Atmospheric Administration (NOAA) - Forecast Systems Laboratory.




Procedure - Part A

Figure 2-4. Neligh, Nebraska Wind Profiler Plot - 12/12/91.
Refer to Figure 2-2 for the Location of Neligh, Nebraska.
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  1. On the Neligh, Nebraska Profiler Plot worksheet, circle the wind barb that represents the maximum (highest) wind speed. Print the label "max" on the circled wind barb.

  2. A weather front is a zone of weather change over a relatively short distance. Wind usually changes across a front. When the wind changes direction, or speed, or both, the weather is changing. Knowing this information helps forecasters predict weather.

    On the Neligh, Nebraska Profiler Plot worksheet from Figure 2-4, beginning at hour 5 and ending with hour 17, draw a heavy dark line along the path where the wind abruptly changes speed and direction. This is the location of a front. Label this line "Front."


  3. A line connecting points of equal wind speed is called an isotach. In this part of the procedure you will draw isotachs on the Neligh, Nebraska Profiler Plot worksheet from Figure 2-4.

    On the the worksheet from Figure 2-4, draw a curved isotach that encloses all wind barbs at or below 20 knots in velocity. Color the area limited by this line violet. Next, draw the isotachs that contain all barbs at and between 25 and 45 knots in velocity. Color this area blue. Repeat this process for the isotachs enclosing all barbs at or between 50 and 75 knots in velocity, and color this area green. Finally, complete the plot by repeating the process for the isotachs containing barbs in the 80 - 100 knot velocity range. Color this area yellow.




Questions - Part A

  1. What is the highest wind speed?_____________________________________________

  2. What is the wind speed and wind direction at the lowest height at 8 hours (0800 UTC)? ______________________________________________________________________

  3. As the front passes from 5 to 17 hours (1700 UTC), what change in wind direction is likely at ground level?____________________________________________________________

    ______________________________________________________________________

    In wind speed?__________________________________________________________

  4. What effect might the passing of the front have on surface temperature?







Figure 2-5. Questions Sheet
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Procedure - Part B

Figure 2-6. Palestine, Texas Wind Profiler Plot - 12/12/91.
Refer to Figure 2-2 for the Location of Neligh, Nebraska.
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  1. On the Palestine, Texas Profiler Plot worksheet, circle the wind barb(s) that represent the maximum (highest) wind speed. Print the label "max" on each circled wind barb.

  2. In this step of the procedure you will draw the isotachs and color each velocity range as in Procedure A. When drawing your isotachs, be sure to include the extreme values of each wind velocity range presented in this part of the activity. After you draw the isotachs for a given velocity range, color the area limited by the isotachs with the color assigned to that velocity range.




Questions - Part B

  1. At what height in kilometers does the maximum wind speed occur?______________________

  2. The jet stream is a high-speed ribbon of air that meanders through the Earth's upper atmosphere. On the Palestine, Texas Profiler Plot, the jet stream is located between the two 100 knot isotachs.

    What is the range for the height of the jet stream? (Hint: Subtract the lowest height from the highest height between the two isotachs.) ________________________________________________________________________

    ________________________________________________________________________

  3. What is happening to the height of the jet stream as time passes from 1 to 12 hours UTC?

    ________________________________________________________________________

    ________________________________________________________________________

  4. What effect might this height change have on local weather at ground level?







Figure 2-7. Questions Sheet
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Conclusions

Review the problem stated in the workstation screen graphic
at the top of this web page and write your conclusions here.



Figure 2-8. Conclusions Sheet
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