It may also be formed when supercooled fog droplets are intercepted by buildings, fences and vegetation. A thin sheet of ice, relatively dark in appearance, may form when light rain or drizzle falls on a road surface that is at a temperature below 0 ☌ or, alternatively, when water already on the road surface subsequently freezes when the temperature thereof falls below freezing point. On lakes, black ice is commonly overlain by white ice formed from refrozen snow or slush. (1) Thin, new ice on freshwater or saltwater, appearing dark in colour because of its transparency, which is a result of its columnar grain structure. See also inflow stinger.Ī theoretical explanation of the process by which precipitation particles may form within a mixed cloud (composed of both ice crystals and liquid water drops). Its size and shape change as the strength of the inflow changes. As with any inflow band, cloud elements move towards the updraft. It is attached to a supercell's general updraft and is oriented roughly parallel to the pseudo-warm front. A particular type of inflow band with a relatively broad, flat appearance suggestive of a beaver's tail. This area often coincides with a radar hook echo and/or a mesocyclone, especially one associated with a high-precipitation (HP) storm. A region of storm-scale rotation, in a thunderstorm, which is wrapped in heavy precipitation. The structure is typically most pronounced on the leading edge of the updraft, while drier air from the rear flank downdraft often erodes the clouds on the trailing side of the updraft. A thunderstorm updraft with cloud striations that are curved in a manner similar to the stripes of a barber pole. This type of cloud must not be confused with snow which is blown off a mountain summit and carried downwind. Stationary orographic cloud which forms in the neighbourhood of a mountain crest or peak and takes the shape of a banner streaming downwind therefrom. A back-sheared anvil often implies a very strong updraft and a high potential for severe weather. A thunderstorm anvil which spreads upwind, against the flow aloft. Frequent (often continuous or nearly continuous), localized lightning discharges occurring from within a thunderstorm anvil.Ī thunderstorm in which new development takes place on the upwind side, such that the storm seems to remain stationary or propagate in a backward direction. See cumuliform anvil, knuckles, mushroom. A circular or semicircular lip of clouds along the underside of the upwind part of a back-sheared anvil, indicating rapid expansion of the anvil. They typically appear during the weakening or dissipating stage of the parent thunderstorm or during an active mesoscale convective system. A lightning discharge occurring within the anvil of a thunderstorm, characterized by one or more channels that appear to crawl along the underside of the anvil. Its glaciated top spreads out horizontally upon reaching the tropopause or by the action of the winds aloft. The process in which solid precipitation particles combine in the atmosphere to produce larger particles, such as hailstones.Ī cirriform cloud with an anvil shape, which forms the upper part of a well-developed Cumulonimbus. The process in which precipitation particles grow by collision with, and by assimilation of, cloud particles or other precipitation particles. Regarding the general distinction between advection and convection, the former describes the predominantly horizontal, large-scale motions of the atmosphere or ocean, while convection describes the predominantly vertical, locally induced motions. temperature, chemical tracers) by the motion of the fluid. ![]() Transport of water or air along with its properties (e.g. Growth of a cloud or precipitation particle by the collision and union of a frozen particle (ice crystal or snowflake) with a supercooled liquid droplet which freezes on impact. The following terms were sourced from the documents indicated at the end of this glossary, sometimes with minor modification, or directly from WMO experts.
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