Warm fronts can be especially dangerous, and notorious in Iowa for tornadoes.
This is a classic Iowa tornado day. Cloudy, cold, drizzly then the sun comes out behind the warm front at the last minute and all hell breaks loose.
Follow the front. Storms that can catch and root on the front will be particularly favored for tornadoes. Where winds are more southeasterly.
Friday when I got to work, I told the others, there won't be a tornado in Des Moines, doesn't feel right, winds are out of the southwest. Areas with surface winds out of the south, but especially southeast are going to have maximized spin, which is why the warm fronts are usually trouble.