Rain and snow mixed and snow. Though no "official" criteria exist for the term, in the United Kingdom the term is not used when any significant accumulation of snow on the ground takes place. It is often used when the temperature of the ground surface is above , preventing accumulation from occurring even if the air temperature is marginally below ; but even then, the falling precipitation must generally be something other than exclusively snow. In the United States, wintry mix generally refers to a mixture of freezing rain, ice pellets, and snow. In contrast to the usage in the United Kingdom, in the
Cumulonimbus and aviation the shear between rising and sinking air. If the airspeed is too high at this point, the airplane will break apart. The crash of Flight AF 447 is indirectly related to this situation: the pilot, being short on fuel, opted for the shortest path while crossing the thunderstorm line associated with the intertropical convergence zone, and the pitot tubes iced over. What followed is known. On-board radars can be deceiving. Hail shafts generate weak radar echoes and are significantly more dangerous than cloudbursts. Close to the ground, heavy rain (or snow at altitude) tends to dampen turbulence (it is said