Northern Utah Mesocyclone

The NWS issued a tornado warning this afternoon for an area including portions of Weber, Davis, and Morgan Counties.

Of concern is one of the best developed mesocyclones (a rotating vortex about 10 km across) I've seen in northern Utah.  Radar reflectivity showed a classic "hook echo" associated with the storm as it impinged on the northern Wasatch near Farmington. 

NWS Doppler radars measure the radial velocity toward or away from the radar, so mesocyclones produce a very clear signature of rotation with a couplet of inbound (green and blue) and outbound (red) velocities colocated with the hook.  This is indicative of the small scale rotation associated with the storm. 

The mesoscale rotation does not necessarily mean that there is a tornado.  About 25% of mesocyclones produce tornadoes, but that's certainly enough to warrant a warning in this case.  

Let's hope this was just a well-developed mesocyclone that didn't produce a tornado.