Around 9:30 tonight, the Denver-Boulder front range was treated to a fairly rare & unusually intense winter thunder-snowstorm! While not the first to happen here, it was the first I had ever seen & reminded me of just how fast weather along the front range can change, even on a seemingly calm & placid winter day...

At 9:20pm, I called my sister who, while driving to Boulder, mentioned seeing large bright flashes from the foothills--probably the very first strokes of lightning from the rapidly developing storm. Within seconds, she started shouting “Lightning!!”, so I bolted out the door camera in-hand, knowing the storm would be over Denver soon!

Denver NEXRAD, 0456UTC (9:56pm MST)                      METARS @ 923pm MST (Courtesy RAP/UCAR)

My first inclination was to get to a local high spot, somewhere with the best overall visibility that I would be able to take stills of the oncoming thunder-snowstorm as quickly as possible. Most thundersnow events don’t last long since they happen in very low-CAPE (instability), high shear atmospheric conditions where the basic ingredients for convection & static discharge (moisture, lift, & instability) are very limited or non-existent. Other sites explain the specifics in more detail (see Wikipedia’s: Thundersnow).

At first, I noticed the intervals/time between flashes was very long: 5-7 minutes (compared to the typical summertime storm, with flash rates anywhere between 5-15 seconds, in general). Also, most of the strikes were intracloud (IC), versus ground strikes (which made sense since most of the static charge was produced within the thunderclouds). As the storm came closer, I shifted east a short way down E-470 & noticed the flash rate increased to every 3-5 minutes. The flash-thunder time also dropped to about 5 seconds--the thunder-snowstorm was almost overhead! I took the top picture around 9:45pm, just as the storm moved off the foothills out over the southern Denver metro. For a brief period (about 20 minutes), the flash rate jumped to 1 IC strike every 3 minutes!! Just after the lightning seemed to hit its peak (a remarkable experience by itself), an intense graupel (soft hail) shaft passed right over me. Watching the soft, rounded graupel the size of small hail with thunder echoing is an experience I won’t forget!