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Freezing Rain
supercooled droplets freezing on impact
Ice storms can be the most
devastating of winter weather phenomena and are often
the cause of automobile
accidents, power outages and personal injury.
Ice storms result from the accumulation of freezing rain,
which is rain that becomes supercooled and
freezes upon impact with cold surfaces.
Freezing rain is most commonly found in a narrow band
on the cold side of
a warm front,
where surface temperatures are at or just below freezing.
The diagram below shows a typical temperature profile
for freezing rain with
the red line indicating the atmosphere's temperature at any given altitude.
The vertical line in the center of the diagram
is the freezing line.
Temperatures to the left of this line are below freezing,
while temperatures to the right are above freezing.
Freezing rain develops as
falling snow encounters a layer of warm air
deep enough
for the snow to completely melt and become
rain. As the rain continues to fall,
it passes through a thin layer of cold air just above the surface
and cools to a temperature below freezing. However, the drops
themselves do not freeze, a
phenomena called supercooling (or forming "supercooled drops").
When the supercooled drops strike the frozen ground
(power lines, or tree branches),
they instantly freeze, forming a thin film of ice, hence freezing rain.
Precipitation
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Dangers
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