Learning Lesson: Sizing Up Hail


OBJECTIVE Train the students better estimate the size of hail.
OVERVIEW Based upon samples picked at random the student learn to estimate the size of hail.
TOTAL TIME 20 minutes
SUPPLIES Sealed box with a small opening and several different size balls made of wood and styrofoam.
PRINTED/AV MATERIAL None
TEACHER PREPARATION Acquire the balls at a local fabric and/or hardware stores. Number the balls with a random values, not associated with size. Record each number and size on your answer key. Place the balls in a box and seal the box leaving an opening just large enough to allow the largest ball to pass through. Collect balls of the following quantities and sizes.
# 3 3 3 3 2 2 2 2 1 1 1
Size ½" ¾" 1" 1¼" 1½" 1¾" 2" 2½" 3" 3½" 4"
SAFETY FOCUS Thunderstorm safety


Background

SKYWARN is a concept developed in the early 1970s that was intended to promote a cooperative effort between the National Weather Service and communities. The emphasis of the effort is often focused on the storm spotter, an individual who takes a position near their community and reports wind gusts, hail size, rainfall, and cloud formations that could signal a developing tornado.

Another part of SKYWARN is the receipt and effective distribution of National Weather Service information. The organization of spotters and the distribution of warning information may lies with the National Weather Service or with an emergency management agency within the community. This agency could be a police or fire department, or often is an emergency management/service group (what people might still think of as civil defense groups). This varies across the country however, with local national weather service offices taking the lead in some locations, while emergency management takes the lead in other areas.

SKYWARN is not a club or organization, however, in some areas where Emergency Management programs do not perform the function, people have organized SKYWARN groups that work independent of a parent government agency and feed valuable information to the National Weather Service.

The information these spotters provide is invaluable to the National Weather Service. We can observe storms from space and peer inside with Doppler radar but it is often the trained spotter's observation that makes helps give us complete the picture of what is happening in a particular location.

Having accurate information is extremely important. Training in estimating the size of hail not only improves the accuracy of the hail report which leads to better weather warnings but also help insure the safety of the spotters by allowing them to observe the hail from a safe shelter.

Procedure

Choose a student to select balls from the box. Once the ball is selected have the student tell the class the number on the ball. The students should write that number on their paper. Pass the ball, row by row, around the class allowing the students to hold it and estimate the ball's diameter in inches. Once the entire class has written their estimates, place it aside.

Repeat the procedure with the next ball chosen from the box. (you can save time by allowing several balls to be passed through the classroom at the same time.) Once the last estimate has been made, tell the students which number ball was which size.

Discussion

Take a poll of the class asking their results of their estimates. For example, hold up a 1" ball and ask

  • How many students had the correct estimate?
  • How many estimated the ball was greater than 1"? If so, by how much?
  • How many estimated the ball was less than 1"? If so, by how much?

Again holding up the 1" ball say the National Weather Service defines a severe thunderstorm as one containing

  • Hail size of 1" or larger, and/or
  • Any wind speed 58 mph or greater.
Fast Facts

On June 22, 2003, a hailstone recovered in Aurora, NE, had a diameter of 7" (17.8 cm) and a circumference of 18 3/4" (47.6 cm). This hailstone was larger than the previous record large hailstone that fell in Coffeyville, KS, in 1970 (5.7" (14.5 cm) diameter and 17.5" (44.5 cm) circumference). However, weight, is the most important measurement. An accurate weight could not be determined for the Aurora hailstone; so the Coffeyville hailstone of 1970 remains the heaviest hailstone weighed and verified in the United States at 1.67 pounds (0.76 kg).

Hail causes $1 billion in damages to crops and property each year.

Hailstones can fall at speeds up to 120 mph (193 km/h).

Costliest United States hailstorm: Fort worth, Texas, May 5 1995. Total damage was $2 billion.


Live Weatherwise

Thunderstorm Safety Rules

When the National Weather Service issues a severe thunderstorm warning it means a severe thunderstorm is occurring, is imminent, or has a high probability of occurring. The warning will contain...

  • County or counties affected by the severe weather event,
  • Warning expiration time,
  • Location and direction of storm movement,
  • Locations in the path of the storm, and
  • Additional information and/or call-to-action statement(s).

Remember, due to the nature of a thunderstorm's size, there may be a severe thunderstorm warning in effect for your county but you may experience mostly blue skies. Know where the storm is in relation to your location and which direction it is moving.

Just because a thunderstorm may not be severe that does not mean cause damage. A thunderstorm can be deadly due to lightning alone. If you can hear thunder, you are close enough to be struck by lightning. Seek shelter indoors immediately and remain indoors until 30 minutes after the last thunder is heard.

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