40 MANUAL OF MARINE METEOROLOGICAL OBSERVATIONS 



5342. Freezing Precipitation. Freezing precipitation is classified as 

 freezing rain or freezing drizzle, as follows: 



5342.1. Freezing Rain. Rain that falls in liquid form and freezes to 

 exposed surfaces. When the fall is so rapid that runoff occurs, the ice will 

 usually appear as glaze. 



5342.2. Freezing Drizzle. Drizzle that freezes Fimilarly to rain, 



5343. Frozen Precipitation. Solid precipitation is classified as follows: 



5343.1. Ice Pellets: Precipitation of transparent or translucent pellets 

 of ice, which are spherical or irregular, rarely conical, and have a diam- 

 eter of 0.2 in. or less. They are of two types: type (a) comprises frozen 

 raindrops or largely melted and refrozen snowflakes (synonymous with 

 "Sleet" in the U. S.) and are reported by using "ww" table figures 23 or 79, 

 as the case may be. Type (b) consists of pellets of snow encased in a thin 

 layer of ice and are reported by using code figures 87 or 88, as appropriate. 



5343.2. Hail. Ice balls or stones, ranging in diameter from that of 

 medium- size raindrops to an inch or more. They may fall detached or 

 frozen together into irregular, lumpy masses. They are composed either 

 of clear or of alternating clear and opaque layers. Hail often accompanies 

 thunderstorm activity. Surface temperatures are usually above freezing 

 when hail occurs. The size is based on the diameter, in inches, of normally 

 shaped hailstones. 



5343.3. Snow. White or translucent ice crystals chiefly in complex 

 branched hexagonal form (six-pointed stars), often mixed with simple crys- 

 tals. Snow occurs under conditions that are similar, temperature excepted, 

 to those of corresponding forms of rain. 



5343.4. Snow Pellets (Soft Hail). White, opaque, round, or occasion- 

 ally conical kernels of snow-like consistency, 1/16 to 1/4- inch in diameter. 

 They are crisp and easily compressible, and they may rebound or burst when 

 striking hard surfaces. They occur almost exclusively in showers. 



5343.5. Snow Grains (Granular Snow). The solid equivalent of drizzle. 

 They take the form of minute, branched, star-like snowflakes, or of very 

 fine, simple crystals. At times they have the appearance of rime. They 

 occur under conditions similar to those of drizzle, except that the tempera- 

 ture is lower. 



5343.6. Ice Prisms. Small, unbranched ice needles or prisms in the 

 form of rods or plates that have a descending motion and that may be ob- 

 served when the sky is clear. Ice prisms are associated with halo pheno- 

 mena and with temperatures near or below -17.8°C (0°F). 



