<P> A storm that produces a significant thickness of glaze ice from freezing rain is often referred to as an ice storm . Although these storms are not particularly violent, freezing rain is notorious for causing travel problems on roadways, breaking tree limbs, and downing power lines from the weight of accumulating ice . Downed power lines cause power outages in affected areas while accumulated ice can also pose significant overhead hazards . It is also known for being extremely dangerous to aircraft since the ice can effectively' remould' the shape of the airfoil and flight control surfaces . (See atmospheric icing .) </P> <P> Freezing rain is often associated with the approach of a warm front, when subfreezing air (temperatures at or below freezing) is trapped in the lowest levels of the atmosphere while warm air advects in aloft . This happens, for instance, when a low pressure system moves from the Mississippi River Valley toward the Appalachian Mountains and the Saint Lawrence River Valley of North America during the cold season, with a strong high pressure system sitting further east . This setup is known as cold - air damming, and is characterized by very cold and dry air at the surface within the region of high pressure . The warm air from the Gulf of Mexico is often the fuel for freezing precipitation . </P> <P> Freezing rain develops when falling snow encounters a layer of warm air aloft, typically around the 800 mbar (800 hPa) level, causing the snow to melt and become rain . As the rain continues to fall, it passes through a layer of subfreezing air just above the surface and cools to a temperature below freezing (0 ° C or 32 ° F). If this layer of subfreezing air is sufficiently deep, the raindrops may have time to freeze into ice pellets (sleet) before reaching the ground . However, if the subfreezing layer of air at the surface is very shallow, the rain drops falling through it will not have time to freeze and they will hit the ground as supercooled rain . When these supercooled drops make contact with the ground, power lines, tree branches, aircraft, or anything else below 0 ° C (32 ° F), a portion of the drops instantly freezes, forming a thin film of ice, hence freezing rain . The specific physical process by which this occurs is called nucleation . </P> <P> Surface observations by manned or automatic stations are the only direct confirmation of freezing rain . One can never see directly freezing rain, rain or snow on weather radars, Doppler or conventional . However, it is possible to estimate the area covered by freezing rain with radars indirectly . </P>

What do you call the rain with ice