ablation
| the process of being removed. Snow ablation usually refers to removal by melting |
accretion
| growth of precipitation particles by collision of ice crystals with supercooled liquid droplets which freeze on impact |
blizzard
| winds of at least 35 miles per hour along with considerable falling and/or blowing snow reducing visibility to less than one-quarter mile for a period of at least three hours. (xtremely cold temperatures often are associated with dangerous blizzard conditions, but are not a formal part of the modern definition.) |
climatology
| the science and study of climate; the aggregate of all weather conditions at a point over a long period of time |
condensation
| the process in which water vapor becomes liquid |
dendrite
| hexagonal ice crystals with complex and often fernlike branches. |
depth hoar
| large (one to several millimeters in diameter), cohesionless, coarse, faceted snow crystals which result from the presence of strong temperature gradients within the snowpack |
evaporation (water)
| the physical process in which liquid water changes into a gas |
firn
| rounded, well-bonded snow that is older than one year |
graupel
| snowflakes that become rounded pellets due to riming. Typical sizes are two to five millimeters in diameter (0.1 to 0.2 inches). Graupel is sometimes mistaken for hail. |
metamorphism
| changes in the structure and texture of snow grains which results from variations in temperature, migration of liquid water and water vapor, and pressure within the snow cover |
precipitation
| the accumulated depth of rain or drizzle and also the melted water content of snow or other forms of frozen precipitation, including hail |
polycrystal
| a snowflake composed of many individual ice crystals |
rime
| a deposit of ice formed when supercooled water droplets freeze on contact with an object |
saturation vapor
pressure (water)
| the maximum amount of water vapor necessary to keep moist air in equilibrium with a surface of pure water. This is the maximum water vapor the air can hold for any given combination of temperature and pressure |
snowboard
| a solid, flat, white material, such as painted plywood, approximately two feet on each side, that is laid on the ground or on the surface of the snow by weather observers to obtain more accurate measurements of snowfall and water content |
snow core
| a sample of snow, either just the freshly fallen snow or the combined old and new snow on the ground, obtained by pushing a cylinder down through the snow layer and extracting it |
snowbursts
| very intense showers of snow, often of short duration, that greatly restrict visibility and produce periods of rapid snow accumulation |
snow density
| the mass of snow per unit volume which is equal to the water content of snow divided by its depth |
snowfall
| the depth of new snow that has accumulated since the previous day or since the previous observation |
snow depth
| the combined total depth of both old and new snow on the ground |
snowflake
| a cluster of ice crystals that falls from a cloud |
snow flurries
| snow that falls for short durations and which often changes in intensity. Flurries usually produce little accumulation |
snow load
| the downward force on an object or structure caused by the weight of accumulated snow |
snow water
equivalent
| the water content obtained from melting |
snowpack
| the total snow and ice on the ground, including both new snow and the previous snow and ice which has not melted |
snow squall
| a brief, but intense fall of snow that greatly reduces visibility and which is often accompanied by strong winds |
sublimation
| the process in which ice changes directly to water vapor without melting, but also in meteorology the opposite process in which water vapor is transformed to ice (also called deposition) |
supercooled
| the condition when a liquid remains in the liquid state even through its temperature is below its freezing point |
supersaturation
| the condition which occurs in the atmosphere when the relative humidity is greater than 100 percent |
surface hoar
| the deposition (sublimation) of ice crystals on a surface which occurs when the temperature of the surface is colder than the air above and colder than the frost point of that air |
vapor pressure
| the pressure exerted by water vapor molecules in a given volume of air |
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