A Deeper Look Into the Workings of Thundersnow in Nor'easters (credit: Dr. Marshall Shepherd)

DISCUSSION: During a given Winter season, it is quite rare for a given region to experience the apex of all Winter-time atmospheric phenomena which is most commonly referred to as thundersnow.  It is a fairly rare Winter-time atmospheric phenomena due to the fact that there are a number of factors which have to come together just right in order for it to occur during a given winter storm.  Attached below are exact excerpts from the article written by Dr. Marshall Shepherd from the University of Georgia which gives absolutely perfect insights into the science behind thundersnow.

"The basic ingredients required for cumulonimbus clouds (with lightning and thunder) are not often associated with winter precipitation events. According to a recent paper in the journal Weather Analysis and Forecasting, there are certain necessary ingredients for thundersnow, and they are not very different than what you expect in warmer season thunderstorms: lift, moisture, and instability. The study of thundersnow in the central United States found that lightning (and thus thunder) happens when convective instability (explained later) is found in the comma-head. In a SUNY-Albany Master's thesis by Kyle Meier, it was found that thundersnow is also common in regions of intense snowfall banding.

Thundersnow storms are often found with lower convective available potential energy (CAPE), which also means weaker vertical motion in the cloud and more shallow cloud tops. CAPE is basically a measure of how potentially buoyant rising air "volumes" might be. For example, the concept of a hot air balloon is that you try to get the balloon warmer (more buoyant) than the air it is rising into. Larger CAPE values mean there is greater potential for the air to rise (and stronger updrafts).

Other conditions associated with thundersnow include surface temperatures at or just below 32 deg F and a sub-freezing air layer from the cloud base to the surface.  Typical thunderstorm electrification usually involves collisions between ice crystals and lumps of ice called graupel. These collisions in the presence of supercooled water (liquid phase though temperature may be below freezing) are the basis for what is called noninductive charging. While this may also be possible in thundersnow, there is likely less supercooled water and possibly more graupel.

An analysis of dual-polarization radar (a new type of weather radar that improves identification of the types of particles in a cloud) in the Weather Analysis and Forecasting finds "the sudden appearance and expansion of radar gates classified as graupel preceded most of the flashes in these cells. Thus, such a signature in the operational HCA (classification system) should warrant more attention for the possibility of lightning production." Interestingly, some of this graupel (a seedling hailstone) may have fallen out of this Nor'easter storm. Folks, that is rare: thundersnow and hail. Professor Bob Rauber at the University of Illinois emailed me shortly after my original post with a series of papers that explain the instability and cloud ice aspects of thundersnow in greater detail."

To learn more about other neat winter weather stories from around the world, be sure to click on the following link: https://www.globalweatherclimatecenter.com/winter​!

© 2018 Meteorologist Jordan Rabinowitz