Dynamical and Thermodynamic Processes Contributing to Thundersnow Events

Thundersnow is often accompanied by mesoscale snowbanding and may be associated with locally heavy snowfall events (6–12 in) and intense snowfall rates (2–3 in h^-1). Given the sensible weather impacts accompanying thundersnow, the contributing dynamical and thermodynamic processes need to be better understood so that forecasters can recognize the various pathways in which thundersnow can occur. Two thundersnow events from the 2012–2013 winter season were recently analyzed. Similarities among the events included near-saturated conditions, weak moist symmetric stability, and strong updrafts, which occurred in the lower-to-middle troposphere over the range of temperatures corresponding to the mixed-phase region of a thundercloud. However, the two events occurred in strikingly dissimilar synoptic-scale settings. Motivated by the recognition that thundersnow can occur in a variety of synoptic-scale settings, current work will seek to establish the regional frequency and variability of thundersnow events across the U.S.

All instances of thundersnow in the continental U.S. spanning the years 1994–2013 are identified from archived METAR surface observations and NLDN data. From these observations, a comprehensive U.S. thundersnow climatology is created and compared with previous climatologies. Gridded datasets from the 0.5° resolution NCEP Climate Forecast System Reanalysis are used to generate constant-pressure and vertical-profile composites of the environment preceding and during the occurrence of thundersnow. The composites will help determine the dynamical and thermodynamic processes that contribute to regional thundersnow frequency and variability. Representative case studies will also be presented to illustrate the various pathways in which thundersnow can occur.