Chapter 9

HISTORICAL HAIL DATA

Goals: To use data derived from the official severe storm archives of the Storm Prediction Center to study the temporal and spatial distribution of thunderstorms that produce large hail.


Data:

Tabular data, by state, of occurrences of hail of diameter at least 0.75 inches during the period 1986-1995. Hail of this size qualifies the thunderstorm as "severe" based on National Weather Service criterion (Alaska and Hawaii are not listed because no hail this large was observed in either state). Although data is available as far back as 1955 in the archives of the Storm Prediction Center, we will use only data observed since 1986 (because this most recent data is the most reliable).

Alabama, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, District of Columbia, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin, Wyoming.

Here is a file of instructions for decoding the tabular information.


Procedure:

Using the hail data provided, answer the following questions:

  1. For the period 1986-1995, determine the number of occurrences of hail of diameter 1 inch or larger in each state. Do the same for hail of diameter 2 inches or larger. What states have the highest frequency of 2-inch-diameter or larger hail?

  2. Because states vary in size, a more accurate measure of hail occurrence would require dividing by the area of the state. What states have the highest occurrence (per unit area) of 2-inch-diameter or larger hail? Does your analysis agree, in general, with Figure 9.7 (which shows the average number of thunderstorm days)?

  3. For each state, determine the time of day when large hail (diameter 2 inches or larger) is most common. Do you see any signs of the effects of MCCs, as is the case in Figure 9.23 (which shows the average time of thunderstorm initiation)? That is, do some states show a maximum (absolute or relative) in the frequency of large hail during the night?

Other "Weather on the Web" Exercises

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