Starting on June 1st, 2009, Western Region National Weather Service Offices will begin issuing severe thunderstorm warnings for 1" hail versus the previous criteria of 3/4" hail. This is being done to better represent hail that produces actual damages and to reduce user complacency to severe thunderstorm warnings. The Central Region National Weather Service offices started this on April 1, 2009, including North and South Dakota.

No change will occur with respect to wind speed criterion for severe thunderstorm warnings, which is wind gusts equal to or exceeding 50 knots or 58 mph.

For thunderstorms expected to produce around 3/4" to 7/8" diameter hail but remain below severe wind thresholds, Weather Forecast Offices will utilize the Special Weather Statement (SPS), headlined as a Significant Weather Advisory. This Significant Weather Advisory will be available on NOAA Weather Radio, to local media outlets and on the Internet.

Weather Forecast Offices will continue to collect and disseminate reports of hail that are 3/4" in diameter or larger using the Local Storm Report.

This experiment was based on feedback from local partners (emergency managers, media, public, etc.), as well as scientific research conducted by Texas Tech University which demonstrated that significant property damage does not occur until hailstone sizes reach 1” in diameter.