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ous. The HRRR can also predict damaging straight-line windstorms called "derechoes" and provide key timing information about when storm severity is increasing and when it's decreasing. It can provide a wealth of information to forecasters about other weather hazards such as narrow heavy snow bands found in winter storms and areas of low ceiling and visibility. This information is vital to safer and more economic planning for transportation, including decisions by pilots and air traffic managers trying to maneuver planes around hazardous conditions.
• Tested and refined across the country for the past two years, including on a number of severe weather events, the HRRR has demonstrated its effectiveness. On June 29, 2012, the HRRR helped identify a major "derecho" severe wind event as it was forming in Illinois and forecast its rapid sweep through Indiana and Ohio during the day and into the Washington D.C. area that evening. It was also instrumental in providing the public with early forecasts of the May 31, 2013 tornadoes in Oklahoma and flash flooding that day.