tornado yesterday in gretna?

i was chatting with a-pry yesterday afternoon before the excitement hit (more on that later) and she mentioned that she thinks i'd make a good teacher. i had just given her and one of the other students a tutorial on doppler radar. and you know, i don't know if i'd make a good teacher, but i sure know i like to teach. i suppose that is, in part, why i agreed to be an instructor for the course.

yesterday afternoon the persistent cloud cleared out of the far southern edge of the province and thunderstorms almost immediately popped up. one storm was in north dakota and very close to the international border. radar was showing severe hail with the storm, so we decided to issue a severe thunderstorm warning for it. well, a few minutes later, i get a call from nws grand forks, telling me that law enforcement was reporting a tornado just southwest of gretna on the american side, heading pretty much straight for gretna. we immediately issued a tornado warning.

a-pry will likely be trying to track down whether or not it was on the ground in canada, but there was certainly some severe weather with the storm. there was hail at least the size of quarters (25 mm) and possibly up to the size of golf balls (40 mm). time will tell.

one of the most interesting things about this storm, though, was the fact that doppler radar was showing anticyclonic rotation inside the storm. conventional wisdom has it that about 1% of all supercells rotate anticyclonically, and even fewer of those produce tornadoes, so we apparently had an extreme anomaly yesterday. i'm glad to report that i captured some of the radar images and they should be posted sometime today on weather central. enjoy!!