National Weather Service United States Department of Commerce

Most damage created by Severe Thunderstorms across Vermont and northern New York is from strong downburst winds. Thunderstorms may also produce hail, which indicates strong vertical motion. Most hail reports in our area are generally 3/4 of an inch in diameter or smaller, and rarely larger than a quarter. Remember, if a thunderstorm produces hail that is 1 inch in diameter (quarter size) or larger, it is considered to be a severe thunderstorm.

The first chart below will assist you in estimating hail size. The second chart below will help in estimating just how strong the winds are. If the winds are 58 mph or stronger, or trees and power lines are blown down, the thunderstorm is considered to be severe.

Another deadly threat of thunderstorms is Lightning. Remember, it does NOT have to be raining for lightning to strike. If you hear thunder, the risk of lightning strikes exists. In Vermont and northern New York, slow moving thunderstorms may also cause Flash Flooding. Campers, hikers and those who live or work near rivers and streams need to be alert to water levels.

1/4" Pea Size
1/2" Mothball Size
3/4" Penny Size
7/8" Nickel Size
1" (Severe Criteria) Quarter Size
1 1/4" Half Dollar Size
1 1/2" Walnut or Ping Pong Ball Size
1 3/4" Golf Ball Size
2" Hen Egg Size
2 1/2" Tennis Ball Size
2 3/4" Baseball Size
3" Teacup Size
4" Grapefruit Size
4 1/2" Softball Size

25-31 mph Large branches in motion; whistling heard in telephone wires
32-38 mph Whole trees in motion; inconvenience felt walking against the wind
39-54 mph Twigs break off trees; wind generally impedes progress
55-72 mph Damage to chimneys and TV antennas; pushes over shallow rooted trees
73-112 mph Peels surfaces off roofs; windows broken; light mobile homes pushed or overturned; moving cars pushed off road
113-157 mph Roofs torn off houses; cars lifted off ground