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New Hail Criteria

The National Weather Service (NWS) Central Region has conducted a demonstration in the state of Kansas and adjoining County Warning Areas over the past four years, utilizing a hail size criterion for issuance of Severe Thunderstorm Warnings of 1” in diameter, rather than the historical 3/4” threshold. 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.

Customer responses have indicated high satisfaction with adoption of the 1" hail criterion. Our media partners said warnings are more meaningful because the public knows there is a genuine risk of damage when a Severe Thunderstorm Warning is issued and fewer complaints are fielded from viewers/listeners of excessive interruptions into programming. Emergency managers agree that warnings carry more weight and credibility.

Based on the favorable response from partners and customers, the NWS Western Region (WR) will implement a similar demo for all 8 NWS WR states, on June 1 to catch the main severe weather season for both the northern tier of NWS WR and the southwest monsoon season. This implementation will also eliminate potential CWA/state border issues between CR and WR offices. Information for organized strong, but less than severe, thunderstorms will be provided via a Significant Weather Advisory. For pulse-type storms of moderate strength that are not expected to last long, NWS offices may issue a Short Term Forecast or a "Significant Weather Advisory".

The wind criteria for issuing a Severe Thunderstorm Warning will remain 58 mph (50 knots).

In CR, previous participating NWS weather forecast offices included Dodge City, Goodland, Topeka and Wichita, Kansas; Hastings, Nebraska; Kansas City and Springfield, Missouri. Participation in the region-wide project will include 38 offices in Colorado, Illinois, Indiana, Iowa, Kansas, Kentucky, Michigan, Minnesota, Missouri, Nebraska, North Dakota, South Dakota, Wisconsin and Wyoming. For Western Region, this will include offices in Arizona, California, Idaho, Montana, Nevada, Oregon, Utah, and Washington.

If feedback in this large area over the next year remains positive, it is expected that the change to one inch hail criterion for severe thunderstorm warnings will be expanded nationwide.

Map of WR offices

US Dept of Commerce
National Oceanic and Atmospheric Administration
National Weather Service
Phoenix Weather Forecast Office
P.O. Box 52025
Phoenix, AZ 85072

Tel: (602) 275-0073

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