Abstract
Simultaneous measurements of ice nuclei have been made at three widely separated sites (city, mountain and coastline) in western Washington for a period of five months in 1968. The ice nucleus counts in the city (Seattle) were considerably greater than those at the two non-urban sites. Moreover, the counts in the city showed peak values when the wind was from the main industrial and urban areas. Ice nucleus counts on the Pacific coast were greatest when the wind was from the mainland.
The effects of synoptic and local weather conditions on ice nucleus counts were also investigated. Arctic air masses which were unmodified by local conditions appear to give low ice nucleus counts. In snow and fog the counts were about one-third those in clear air. In some cases the ice nucleus count increased sharply in rain showers and also when fogs dissipated.
