sentences:  The usage of tornado emergencies to alert major population centers to the imminent threat of a catastrophic tornado impact has also led to the development of the flash flood emergency which is similarly employed when severe flash floods threaten populated areas.The National Weather Service Weather Forecast Office in Des Moines, Iowa is one of the forecast offices to have created a set purpose and criteria for the usage of "tornado emergencies" in tornado warning products, which were made effective on March 12, 2010.According to the Des Moines office, the purpose of the tornado emergency wording is as follows