The agency also confirmed a twister in the northwestern Illinois county of Carroll.

CNN: More storms expected after tornadoes kill 2 in Oklahoma

Constable Stephen Carroll was murdered by dissident republican paramilitaries in County Armagh on 9 March 2009.

BBC: Constable Stephen Carroll

Kate Carroll, whose husband Stephen was shot dead by the Continuity IRA in Craigavon, County Armagh, in March 2009, lit a candle to remember officers who have died in Northern Ireland.

BBC: Police sacrifice honoured at memorial day in Belfast