Storms Crossing a Warm Front
Thunderstorms formed north of Fargo, ND on May 8, 2005. As the storms
moved northward, they got enhanced by convergence and maybe enhanced
low-level flow (i.e. helicity) when they crossed the warm front.
While there were no reports of them, if these storms were to be
tornadic, this would be the optimum time. The storms crossed the warm
front between about 22Z (western storms) and about 23Z (eastern
storms).
Dewpoints at the time were in the 10 to 12°C range--not too impressive.
Had there been more moisture present, tornadoes would have been more
likely. As it is, though, watch the shape of the strongest storm at
22:04Z. It shows that supercell kidney bean shape, although the
storm-relative velocities didn't show any rotation.
The largest hail reported from these storms was the size of golf
balls--about 40 mm in diameter.
Storm reports can be found here.