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3.4.2
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Freezing Precipitation.
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3.4.2.1
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Freezing Drizzle. Drizzle, the drops of which freeze on impact with the ground or with other objects at or near the earth's surface.*
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3.4.2.2
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Freezing Rain. Rain, the drops of which freeze on impact with the ground or with other objects at or near the earth's surface.*
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3.4.2.3
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Freezing Drizzle or Freezing Rain shall be reported when rain or drizzle is freezing on the Ice Accretion Indicator or on other objects at or near the earth's surface.*
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3.4.3
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Frozen Precipitation.
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3.4.3.1
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Snow. Precipitation of mainly hexagonal ice crystals, most of which are branched (star-shaped). The branched crystals are sometimes mixed with unbranched crystals. At temperatures higher than about -5C, the crystals are generally clustered to form snow flakes.
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3.4.3.2
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Snow Pellets. Precipitation of white and opaque particles of ice. These ice particles are either spheical [sic] or conical; their diameter is about 2-5 mm.
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3.4.3.2.1
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Snow pellets are brittel and easily crushed; when they fall on hard ground, they bounce and often break up. Snow pellets always occur in showers and are often accompanied by snow flakes or rain drops, when the surface temperature is around 0C.
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3.4.3.3
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Snow Grains. Precipitation of very small white and opaque grains of ice. These grains are fairly net or elongated; their diameter is generally less than 1 mm. When the grains hit hard ground, they do not bounce or shatter. They usually fall in very small quantities, mostly from Stratus or from fog, and never in the form of a shower.
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3.9
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Intensity of Precipitation
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3.9.1
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The precipitations classified above as Liquid, Freezing and Frozen (with the exception of ice crystals) are always qualified as to intensity, viz., very light, light, moderate or heavy.
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3.9.2
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VERY LIGHT is used to indicate the intensity when scattered drops, flakes, grains, pellets or stones are occurring at a rate which would not wet or cover a surface, regardless of the duration.
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3.9.3
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The intensities LIGHT, MODERATE and HEAVY are determined by considering either the effect on visibility or the rate of fall.
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3.9.4 |
Intensity by Visibility Criteria.
| Snow |
LIGHT if visibility 5/8 mile or more |
| Snow Shower |
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| Snow Grains |
MODERATE if ALONE* and the visibility reduced to 1/2 or 3/8 mile |
| Snow Pellets |
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| Drizzle |
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| Freezing Drizzle |
HEAVY if ALONE* and visibility reduced to 1/4, 1/8 or 0 mile. |
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* It is of course assumed that the objects are not artifically [sic] heated above or cooled below the temperature of the ambient air.
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