Microphysical Influences on Ensemble Members in the December 15-16, 2013 OWLeS Case

The eastern Great Lakes regions has served as a hotspot for some of the most intense lake-effect snow systems on record. With lakes such as Erie and Ontario being the host to long-lake-axis parallel showbands, large amounts of snow can affect these regions in just a short amount of time. The December 15-16^th, 2013 lake-effect snow system left upwards of 20 inches of snowfall over Western New York in just a 24-hour period, leaving much of this region incapacitated. This event was the last of three lake-effect and synoptic snow systems to have struck this region during that week. We will focus of the snow band just east of Lake Ontario which produced the highest snowfall accumulations of 23 inches over the Tug Hill Plateau. At times, this lake-effect band had snowfall rates of around three to four inches per hour. In this study we will take an in depth look at the microphysical factors that can affect both the location of these bands as well as the snowfall accumulations associated with the December 15-16^th, 2013 Ontario Winter Lake-effect Systems (OWLeS) field campaign. Microphysical factors we will examine include fall speed, condensation nuclei type, crystal shape, ice nuclei concentrations and number of moments for this study. In an attempt to visualize and compare these impacts, a 19-member physical ensemble was developed. Ensemble members were created by running the Weather Research and Forecasting Model using National Taiwan University’s microphysical scheme as well as various other microphysical schemes. This ensemble provides an opportunity to investigate observed microphysical processes associated with this lake-effect system and allows us to directly compare various sensitivities to different microphysical factors and schemes. Through this physical ensemble it was found that microphysics significantly influenced snowfall accumulations, while the location of these bands could be attributed to the overall dynamics of such lake-effect systems. It should also be noted that in this study precipitation production was found to be highly sensitive to such factors as fall speed and number of moments.