The collection procedure consisted of placing a thin layer of methyl cellulose solution (Tissue Tek) on a flat copper plate (15 mm x 27 mm) that was precooled to the ambient outdoor temperature. Newly fallen snowflakes were either allowed to settle on the surface of the methyl cellulose solution or were lightly brushed onto its surface and then rapidly plunge frozen in liquid nitrogen LN2 at -196° C. When samples were obtained from snowpits, a precooled scalpel was used to gently dislodge a sample from the pit wall onto the plate that was either rapidly plunged into a styrofoam container containing LN2 or placed on a brass block that had been precooled with LN2. After a few minutes in LN2 the plates were inserted diagonally into 20 cm segments of square brass channelling and lowered into a dry shipping dewar that had been previously cooled with LN2. The dewar was either transported by van or shipped by air, from remote locations to the laboratory in Beltsville, Maryland. Upon reaching the laboratory, the samples were transferred to a LN2 storage dewar where they remained for as long as one year before being further prepared for observation with LTSEM.