Thundersnow

KUTV viewers are the best! Ben Agi and his wife captured our #thundersnow in SLC! ⚡️❄️ #utwx pic.twitter.com/6z3ZrvnOts

— Chase Thomason (@ChaseThomason) December 15, 2021

Tuesday night's thundersnow event got quite a bit of attention and is even discussed in this article in today's Salt Lake Tribune.  If you want a deep dive, see An Overview of Thundersnow, and article by David Schultz and James Vavrek that appeared in the journal Weather.  I'm able to access it from my campus office this morning, but there is a chance it is paywalled.  

Thundersnow is uncommon, but if you are looking for it, Utah is actually a pretty good place.  The map below shows the number of thundersnow occurrences across the United States from 1961-1990.  The highest number was in Utah and the adjoining Intermountain West.  The upper midwest and the Great Lakes regions are also favored for thundersnow.  

Source: Schultz and Vavrek (2009)/Market et al. (2002)

Thundersnow is basically a thunderstorm with snow falling at the surface.  The key ingredients are instability, moisture, and lift.  Basically, you need a strong updraft and a cloud with a mixture of ice and liquid water to promote electrification and charge separation.  As noted in the Schultz and Vavrek article, collisions between graupel and other ice particles are thought to promote storm electrification and charge separation.  

In northern Utah, thundersnow can be produced by frontal systems, as was the case Tuesday night, lake-effect storms, orographic storms, or other types of convective storms.  To me, the interesting thing about thunderstorm isn't that it happens at all, but that it doesn't happen more frequently.  

The map above could use updating.  It is based on weather observations collected primarily at airports. A new thundersnow analysis could integrate data from lightning detection networks and radar-derived precipitation type analyses, which would likely result in an improved climatology.  I suspect such an approach would show, for example, a pronounced maximum in thundersnow events downstream of Lakes Erie and Ontario.  One can see the former above, with Buffalo reporting six events, but in the case of the latter, there were no reporting stations east of Lake Ontario.  

As is the case in summer thunderstorms, it is best to move inside if you hear thundersnow.  The ski areas will typically get everyone off the lifts and shut them down during thundersnow events.  Nobody is happy when that happens, as the skiing is often quite good with heavy snow, but it is necessary for safety.