Multi‐Year Analysis of Rain‐Snow Levels at Marquette, Michigan

Abstract

AbstractThis study uses observations from a ground‐based instrument suite to investigate the rain‐snow level (RSL) in stratiform rainfall from January 2014 to April 2020 in the Upper Great Lakes Region. The height above the surface where ice melts to rain, the rain‐snow level, influences microphysical assumptions in remote sensing precipitation retrievals and the ability of space‐based radar to discriminate surface precipitation phase because of ground clutter. The instrument suite is installed at the Marquette, MI (MQT) National Weather Service station adjacent to Lake Superior. Rain events and the RSLs are studied through a ground‐based vertically profiling radar (Micro Rain Radar), a custom NASA‐developed video disdrometer (Precipitation Imaging Package), and reanalysis products from ECMWF ERA5 and NASA MERRA‐2. Distinct macro and microphysical characteristics are observed in precipitation events with shallow RSLs (<1.8 km above ground level [AGL]) and intermediate RSLs (>1.8 km AGL). Intermediate RSLs correspond to rain events with relatively higher rain rates and a higher concentration of small drops in the drop size distributions (DSDs). Shallow RSL DSDs contain relatively higher concentrations of large drops with lower fall speeds suggesting that partially melted snowflakes may be reaching the surface. Reflectivity‐rain‐rate relationships are also impacted by microphysical differences associated with RSL regimes. Radar‐detected RSLs agree with reanalysis‐derived melt levels‐especially at wet‐bulb isotherms of 0.5°C and 1°C. Seasonal differences such as shallow RSLs in winter, fall, and spring have subsequent implications for satellite detectability.