Snow surveys by designated stations are made at regular intervals during the winter months to determine the water equivalent (mm) and depth of the snow pack (cm). 5 points (30 m apart), measurements t
aken on the 1st, 8th, 15th and 23rd of each month. 10 points (30 m apart), measurements taken on the 1st and 15th days of each month.
An automated network of snowpack data collection sites. The Natural Resources Conservation Service (NRCS), formerly the Soil Conservation Service (SCS), has operated the Federal-State-Private Cooperat
ive Snow Survey Program in the western United States since 1935. A standard SNOTEL site consists of a snow pillow, a storage type precipitation gage, air temperature sensor and a small shelter for housing electronics.
The trails of precipitation that emerge from the base of generating cells typically observed on time-height displays from vertically pointing radars. (Also called streamers.) Snow trails are also comm
only 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.
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.
An oligochaete worm that lives on temperate glaciers or perennial snow; there are several species that range in color from yellowish-brown to reddish-brown or black; they are usually less than 1 milli
meter (0.04 inch) in diameter and average about 3 millimeters (0.1 inch) in length; some feed off red algae.