Month: January 2010

National Weather Services uses Haag Research to Change Thunderstorm Criterion

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 by core
partners in emergency management and the media. Particularly in areas
of the Central U.S., the frequency of severe thunderstorm warnings
issued for penny-size and nickel size hail might have desensitized the
public to take protective action during a severe thunderstorm warning 

areas that experimented with changing to the one inch hail criterion,
media partners stated their user feedback suggests warnings are now
more meaningful. In addition, television networks receive fewer viewer
complaints from breaking into programming for non-damaging storms.  The
Emergency Management community in those areas agreed that warnings
carry more weight, and spotters now concentrate on the more significant