18 Nebraskaland • November 2020
IN THE FIELD
A thick glaze of ice on the landscape. Bent trees and
downed power lines. Hazardous road conditions. What does
this make you think of? Your answer is probably freezing
rain. Precipitation takes on many different forms throughout
the year and these are determined by the state of our
atmosphere.
One type in particular is quite unpleasant when you're
caught outside in it. As the name implies, this type of rain is
unique in that it freezes on contact. The reason is more than
just a chilly surface around you. The air above you plays a
significant role.
Think of a cylinder stretching above your head all the
way through the atmosphere. When that cylinder has a
shallow layer of sub-freezing temperatures near the ground,
a deep layer of warm temperatures that are above freezing,
then another shallow cold layer to cap the cylinder, that is
when freezing rain occurs. The precipitation can begin their
fall as either rain or snow, pass through a warm layer and
then a second cold layer before meeting the surface. Water
drops freeze on contact in this environment. You'll find this
setup to occur in a narrow strip in advance of a warm front
associated with a low pressure system moving through
during the colder time of year (fall, winter and spring).
Another setup that causes freezing rain is when the
surface is near freezing, but not saturated, and some of the
rain droplets evaporate as they near a surface. Evaporation
causes cooling to a point below freezing, and this can
confound new weather forecasters when they receive reports
of freezing rain, yet the air temperature is above or just at
freezing. Regardless of the cause, freezing rain is a dangerous
condition hampering travel and our comfort.
Martha D. Shulski, at the University of Nebraska-Lincoln, is
the director of the Nebraska State Climate office.
By Martha D. Shulski
WHEN LIQUID TURNS TO SOLID
PHOTO
BY
ERIC
FOWLER
