Tornado sirens are sounding in the City of Knob Noster.  A police dispatcher said the alarms were activated around 4:30 p.m. Monday.  Johnson County has been placed under a severe thunderstorm warning until 5:30 p.m.  A tornado watch is in effect until 10 p.m. for much of the KMZU listening area.  In the event of a tornado, residents should seek shelter in an interior room on the lowest level.