Name_______________________________Date_______________Period__________

Part B - Interpreting Local Weather Radar Imagery Local Weather Radar Imagery Activity

INVESTIGATION

What do weather radarscope views show?

OBJECTIVES

After completing this activity, you should be able to:

• Locate areas of precipitation by interpreting a radar image.
• Determine the areas of most intense precipitation.
• Track precipitation echoes as they move across the field of view of a local weather radar: observe changes over time; make predictions.

PROCEDURE

1. On a day when precipitation is falling across the Washington, D.C. metropolitan region, access and interpret a current local weather radar image from one of the following sources of near-real-time weather radar imagery:
   1. Media General Cable Channel 102 WRC-TV Doppler weather radar display of base reflectivity (very low-tech, but you must have classroom access to cable television)
   2. Doppler weather radar display of base reflectivity, National Weather Service Forecast Office, Sterling, VA

   Alternatively, if precipitation is not falling where you live, then you may want to access Doppler weather radar imagery from the NWS national network of local radars for other regions of the United States where precipitation is occurring. Before deciding which local radars to access, you may find it helpful to refer to a National Radar Summary map.

2. Answer the following activity questions.

QUESTIONS

1. What is the three-letter location identifier (or LOCID) for the Sterling, VA NWSFO Doppler weather radar?

2. What is the date and local time of the radar image? You may need to convert the time from UTC (GMT) to Eastern Standard Time (EST) or Eastern Daylight Time (EDT) by referring to the time conversion chart.

3. In what "mode" is the radar (Precipitation Mode, Clear Air Mode, or Severe Weather Mode)?

4. What is the fractional scale of the radarscope map display? (You may need to refer to a brief tutorial on determining fractional scale.)

5. What is shown on the local weather radarscope--does the radar detect both clouds and precipitation?

6. What kind of precipitation do you think might be occurring when there are radar echoes indicating several levels of precipitation intensity, especially higher DBZs?

7. Interpreting weather radar imagery:
   1. What are the shapes of the precipitation echoes (area echoes, cells, or lines of cells)?
   2. Using only the information provided on the local radarscope, can you determine what type of precipitation is falling (e.g., rain, snow, thundershowers, etc.)?
   3. Is the radarscope view consistent with your own observations, i.e., if precipitation is falling where you live, does it appear on the radarscope for your location?
   4. What is the precipitation intensity reported for your location (in DBZ)?
   5. Find the most intense precipitation echo(es) within the field of view.
      1. In which state(s) and county(ies) is it located?
      2. In what direction and how far from the radar site (LWX) is it located? Give the direction relative to the radar site (N, NE, E, SE, S, SW, W, NW) and the range (distance from the radar site to the precipitation echoes) in kilometers.

8. Do radar echoes change over time?
   1. If two or more consecutive radar pictures are available, what is the direction and speed of movement of precipitation echoes across the region?
   2. According to the sequence of pictures, as time passed, did the intensity of precipitation increase, decrease, or remain the same? (You may answer this question specifically for the location in which you live, or for the entire region.)

9. Compare the local radarscope view to a current surface weather map. How do areas of precipitation relate to large-scale weather systems such as Highs, Lows, and fronts?

FOR FURTHER THOUGHT:

If one assumes that the Earth is flat, and we assume that the radar beam is tilted at an angle of .5 degrees (the lowest angle at which the radar scans the sky), then approximately how many miles from the radar site would the radar beam "overshoot" the tops of precipitation-producing clouds with maximum tops of 10,000 ft? Convert your answer to kilometers (1 mi = approx. 1.6 km, 1 km = 0.6 mi). Can you explain why the outermost range circle on the radarscope is 230 kilometers from the radar site?

                      Connect dots to
                      draw Hypotenuse
                              |
                              v         .      |      Precip.-producing
                              .                | "O"  clouds--maximum
    Radar beam ---> .__________________________|      tops: 10,000 ft
    tilted .5 deg.  ^             ^ "A"
                    |             |
                Radar site        |
                                  |
                      Distance from radar site
                      (solve for this number)

    Hint: Tan.5 = O/A (solve for A)
      Where:
        Tan.5 = the Tangent of an angle of .5 deg.
            O = side of triangle Opposite the angle of .5 deg.
            A = side of triangle Adjacent to the angle of .5 deg.
                (remember that the Hypotenuse is the side of the
                triangle opposite the 90 deg. angle)