In April, 1999, nineteen organizations from the United States and Canada collaborated to conduct the Mt. Washington Icing Sensors Project, or MWISP. Funded principally by NASA and the FAA, MWISP was conceptually modeled from NCAR’s Winter Icing and Storms Program, WISP, conducted in the early 1990s in Colorado and Wyoming. However, MWISP had a narrower focus, principally to evaluate methods of remotely sensing inflight icing conditions. The project was conducted in a rugged mountain environment in New Hampshire where icing is typically more severe, and consisted of one month of intensive observations. Details of MWISP’s design and conduct are described in detail by Ryerson et. al. (2000). The purpose of this paper is to highlight the most significant results of the field program.

MWISP consisted of in situ and remote sensor measurements of icing cloud microphysics. In situ measurements verified remote sensing instruments, and provided comprehensive measurements of cold cloud microphysics in a mountain environment. We will summarize measurements made by CRREL of cloud microphysics at the Mt. Washington summit, particle and drop size spectra created for each 5-minutes of observation, and time series created by Plymouth State College of particle types using image recognition software. In situ instruments that were being development and proven at MWISP are also discussed. ATEK’s icing radiosonde, now being commercialized, provided 29 profiles of supercooled liquid water with height to verify remote sensing system measurements. The Desert Research Institute also tested their hot plate rain and snow gauge, and anemometer, for winter weather applications, and developed final design changes based on MWISP measurements.

Several advances in radar, microwave radiometry, and lidar measurement of icing conditions that occurred as a result of the MWISP field program are also presented. The most noteworthy achievement is NOAA-ETL’s proof of concept of a dual-polarization radar technique for reliably estimating and differentiating ice hydrometeors and supercooled large drops. As a result, NOAA is building the Ground-based Remote Icing Detection System, GRIDS, with FAA funding for potential prototype fielding in two years. In addition, NOAA used their Ka band radar to assess Mt. Washington wind flow dynamics. The Defense Research Establishment at Valcartier, Quebec, demonstrated that wide, angular scans with their lidar allowed fuller characterization of raindrops and ice crystals. Finally, the University of Massachusetts and Quadrant Engineering team demonstrated the capability of their multiple radar band, neural network based, liquid water and drop size retrieval techniques that are now being developed into a prototype airborne icing detection system.

Since MWISP, the Alliance Icing Research Study, AIRS, a larger field program with similar goals, was conducted in Canada during the winter of 1999-2000. AIRS-2 is planned for the winter of 2003-2004. Thus, MWISP is one of a growing series of icing-focused field programs that are improving understanding of aircraft icing microphysics, and substantially aiding the development of inflight icing remote sensing technologies.