Why One Inch Hail Criterion? Figure: The minimum size hail
criterion for severe thunderstorms changes from 3/4 inch (penny-
size) to 1 inch (quarter-size) nationwide on January 5, 2010.
Previously, the National Weather Service (NWS) issued Severe
Thunderstorm Warnings whenever a thunderstorm is forecast to
produce wind gusts to 58 miles per hour (50 knots) or greater
and/or hail size 3/4 inch (penny-size) diameter or larger. For
the past few years, offices that cover areas of Kansas have
experimented using a warning criterion of one inch diameter
hail. During the spring and early summer of 2009, this
experiment expanded to other areas in the Central and Western
U.S. Beginning January 5, 2010, the minimum size for severe hail
nationwide increases to one inch (quarter-size) diameter. There
will not be a change to the wind gust criterion of 58 mph. This
change is based on research indicating significant damage does
not occur until hail size reaches 1 inch (quarter-size) in
diameter, and as a response to requests