 Inseparable said 988 centers should be answering 90% of calls received in-state. In May, Nebraska answered 87% of 2,300 calls, and 988 centers nationwide answered 88% of nearly 388,000 calls. Weather researchers at Iowa State University say a shifting climate and warmer ocean temperatures are partially responsible for a record number of tornadoes this spring. More than 100 were reported in Iowa in May alone.