| Section S | S index | 581-589 of 1376 terms |
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snow stake—(Also called snow scale.) A wooden scale, calibrated in inches or centimeters, used in regions of deep snow to measure its depth. The scale is bolted to a wood post or angle iron set in the ground.
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snow trails—(Also called streamers.) The trails of precipitation that emerge from the base of generating cells typically observed on time–height displays from vertically pointing radars. Snow trails are also commonly observed on range–height indicator displays. Snow trails emerge from a layer of convective instability that often exists in the middle or upper troposphere in widespread storms. Small convective cells developing within this layer produce the ice crystals that then fall to lower altitudes. The base of the convectively unstable layer is called the snow- generating level. The shape and vertical extent of the streamers depend on the vertical profiles of wind and relative humidity in the layer through which the precipitation falls.
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snow tremor—A disturbance in a snowfield caused by the simultaneous settling of a large area of thick snow crust or surface layer. It occurs when wind action has maintained the top foot or more as closely packed, fine-grained snow rather impervious to air movement. Meanwhile, at lower depths, firnification has caused the larger crystals (depth hoar) to grow at the expense of smaller ones, creating air pockets and a weak structure. The collapse of this structure (a perceptible drop, but rarely as much as 1 in.) may be accompanied by a loud report; over a large, level field, adjacent patches may settle as a series of tremors. Occasionally, a snow geyser may be blown upward through the crack of a settling patch.
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snow—Precipitation composed of white or translucent ice crystals, chiefly in complex branch hexagonal form and often agglomerated into snowflakes. For weather-observing purposes, the intensity of snow is characterized as 1) light when the visibility is 1 km (5/8 statute mile) or more; 2) moderate when the visibility is less than 1 km (5/8 statute mile) but not more than 1/2 km (5/16 statute mile); and 3) heavy when the visibility is less than 1/2 km (5/16 statute mile).
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snowcreep—An extremely slow, continuous, downhill movement of a mass of snow.
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