& Technical Tips
Computation & Estimation
What is the National Radar Summary map; what does it show?
After completing this activity, you should be able to:
- Describe the National Radar Summary map: explain how the map is
prepared and what it shows. (Be sure to relate the local radarscope view
to the National Radar Summary map.)
- Locate areas of precipitation by interpreting a National Radar Summary
- Determine the areas of most intense precipitation.
- Track precipitation echoes as they move across the National Radar
Summary map: observe changes over time; make predictions.
- Explain how areas of precipitation relate to large-scale weather
systems such as Highs, Lows, and fronts (by comparing the National Radar
Summary map to a current surface weather map).
- Explain how areas of precipitation relate to areas of cloud cover (by
comparing the National Radar Summary map to a current infrared weather
External links will open automatically in a second browser window;
subsequent clicks on external links will replace the contents of the
second window. This enables the user to keep both the activity and related
graphics on the desktop.
Provide each student with a hardcopy of the activity Answer Sheet.
- Read the Introduction to Weather Radar. Alternate resource:
Introduction to Remote Sensing (see "Doppler
- Download a current National Radar Summary map (or use a map provided by
your instructor). Note: By clicking anywhere on the map, you can zoom in
to a regional radar map showing a smaller area in greater detail.
- Answer the following activity questions. Base your answers upon your
interpretation of the weather graphics that are hyperlinked within each
question, as well as supplemental information presented in the sidebar
(shown left). Record your answers on the National Radar Summary
mi = km x 0.621
km = mi x 1.609
Weather Calculators, courtesy National Weather
Service, Sterling, VA. See "Wind Speed Conversions."
- Local Radar Imagery versus National Radar Summary map:
- What is the approximate maximum range of coverage for NWS
local radars (in miles and kilometers)?
- Is there a single National Weather Service radar capable of scanning
the entire United States for precipitation echoes?
You may need to convert the time from GMT (UTC) to Eastern Standard Time
(EST) or Eastern Daylight Time (EDT). Refer to the time conversion table.
- What is the date and local time of the National Radar Summary map?
On the National Radar Summary map, the heights of storm
cloud tops are shown in hundreds of feet, with the last two zeroes
omitted. For example, 300 = 30,000 ft.
- Where is precipitation occurring?
- Using the following table of two-letter abbreviations for state names,
cross-off all of the states in which precipitation is occurring. You may
need to refer to a map
of the United States (courtesy National Geographic Society) and/or a
map of two-letter abbreviations for
Two-Letter Abbreviations - State Names
- According to the National Radar Summary map, is precipitation falling
where you live?
- What is the maximum cloud top reported?
- What is the general relationship between precipitation intensity and
the height of storm cloud tops?
- Using only the information provided on the National Radar Summary map, for those areas showing
precipitation echoes, can you determine what type of precipitation is
falling (e.g., rain, snow, thundershowers, etc.)?
Measure the distance that precipitation echoes move from the beginning to
end of the animation.
Speed = Distance/Time
60 mi/6 hr = 10 mi/hr
Scale of the Map
Before you can measure distance on the map, you will need to determine the
scale of the map. You may need to refer to a brief tutorial on determining fractional scale. To measure
a real world distance to use to calculate the scale of the National Radar
Summary map, you may need to refer to a map of the United States, courtesy National
Nautical Miles (knot)
mph = knot/0.87
knot = mph/1.15
kmph = knot/0.54
knot = kmph/1.85
- Do radar echoes change over time?
Download a current USA radar map, courtesy WSI Corp. Intellicast.
Follow the link to Start Looping (located at the top of the map), in
order to display an animated GIF of the past two hours of
national radar summaries. Note: By clicking anywhere on the USA radar map,
you can zoom in to a regional radar map, that is also animated. Optional:
Follow the link to Interactive Loop, featuring a button for a 12-hour
- What is the direction (N, NE, E, SE, S, etc.) and speed of movement of
precipitation echoes across the United States (in mi/hr or km/hr)?
Hint: Verify your answer by comparing it with the
arrows showing direction of cell movement and speed (in knots) on a
current National Radar Summary map.
- According to the sequence of maps, make a precipitation forecast for
your location. If precipitation is currently occurring, then
predict how much longer the precipitation will occur. If precipitation
is not currently occurring where you live, then predict when the
next precipitation event might begin. Your forecast should be based (in
part) upon the direction and speed at which observed precipitation echoes
are moving (refer to Question 5a).
The USA radar map used in Questions 5 & 6 is a "value-added"
product that utilizes surface weather observations to verify the type of
precipitation observed by a national network of local weather radars.
- Compare the USA radar map to a current surface weather map. How do areas of
precipitation relate to large-scale weather systems such as Highs, Lows,
On black and white infrared weather satellite images, higher (colder)
cloud tops appear white or shades of light gray. On enhanced infrared
images, the highest (coldest) cloud tops appear as shades of dark gray to
black embedded within areas of white; color-enhanced IR images often show
the highest cloud tops as shades of yellow, orange, or red.
- Compare the USA radar map to a current infrared weather satellite image.
- Do all clouds produce precipitation?
- Can you infer the general relationship between the temperature of
storm cloud tops (e.g., thunderstorm cells) and precipitation