The National Weather Service, Chicago will change the severe thunderstorm warning criteria for hail from 3/4 inch to 1 inch, effective April 1, 2009.
The National Weather Service still encourages Skywarn storm spotters to report hail of all sizes, and to accurately measure hail to the nearest quarter of an inch. One inch diameter hail is roughly the size of a quarter. Wind criteria for a severe thunderstorm will remain 58 mph or greater (50 knots).
View the video about the new hail criterion.