An urban-based climatology of winter precipitation in the northeast United States

Varying forms of precipitation during winter weather events cause disruptions to commercial operations and transportation networks, particularly in densely populated regions. Developing a better understanding of the characteristics surrounding these events may lead to better prediction and subsequent mitigation. This study constructs a 21-year cold season climatology of precipitation type over highly urbanized areas of the northeastern United States. By using quality-controlled station reports, a specific focus is placed on the influence of urbanization in precipitation processes. In events involving multiple precipitation types, the ambient atmospheric profile is very close to the freezing point in lower levels. The influence of the boundary layer urban heat island may play a role in increasing melting of hydrometeors. Statistically significant findings from linear regression modeling show that proximity to urban centers, as derived from mean road density, plays a role in the surface observation of mixed precipitation events. 21% of any mixed precipitation observation may be attributed to its distance from a high density urban area. Decreases in mean surface wind speed and direction during mixed precipitation events increase the likelihood of an intact boundary layer urban heat island and melting of hydrometeors when compared to stronger wind speeds during snowfall events.