In Central Virginia the National Weather Service currently defines Severe Thunderstorms as ones containing winds of 58 miles per hour or higher and/or 3/4 inch hail (approximately the size of a dime) or larger. However, this will be changing beginning January 1, 2010. Minimum wind-speeds of 58 miles per hour for Severe Thunderstorms will remain the same, but severe hail criteria will change. Instead of 3/4 inch hail, a thunderstorm must contain hail of 1 inch (approximately the size of a quarter) or greater.

So you may be wondering what's up with the change… The National Weather Service has 2 main reasons.

1. There are concerns about the public becoming desensitized by numerous warnings being issued for marginal hail sizes.
2. A Texas Tech research study, "Hail damage threshold sizes for common roofing materials" (Marshall, T.P., Richard F. Herzog, and Steven K. Smith, 2002:, 21st Conference on Severe Local Storms, San Antonio, TX) cited laboratory tests of numerous types of shingles. These tests showed hail damage to shingles and other roofing materials usually begins with hail of 1-inch in diameter.

After this change begins in 2010, the average number of Severe Thunderstorm Warnings for our region are likely to go down.

Below are examples of 3/4 inch hail (left) and 1 inch hail (right)...