What are the differences between winter precipitations?
Answered by Justin Caudell
As the temperatures are on the rise this summer, let’s think about cooler days in the
mountains and the precipitation that comes with it, because after all, winter will be here
before we know it. In the Carolinas, winter brings different forms of precipitation and this
week I will break down a few of the commonly seen types of winter weather and how
they are formed.
Freezing Rain
Freezing rain occurs in the wintertime when rain produced in a warm air mass falls
through a shallow cold air mass below it, freezing on contact with the ground and other
objects if the temperature is below 32 degrees Fahrenheit. The cold air layer has to be
shallow enough so that the rain falling through it doesn't have time to freeze before it
reaches the surface. If the cold air is thick enough, the rain freezes to form ice pellets
instead. If more than about a half inch of ice accumulates, tree limbs, branches, and
power lines start to snap. The resulting damage can cost millions of dollars, and it can
be many days before downed power lines can be fixed to restore power to homes and
businesses. Freezing rain is commonly seen in the northeast part of Georgia and
boarding counties between North Carolina and South Carolina.
Sleet
Ice pellets, or sleet, frequently occurs when it is mixed in with freezing rain. Sleet is
composed of frozen raindrops. Sleet forms in advance of a warm front in the wintertime
in a narrow band, usually sandwiched between an area of snow and an area of rain or
freezing rain associated with an extratropical cyclone. An extratropical cyclone is a low
pressure area that forms near the boundary between warm and cool air masses. Sleet
begins when rain is produced in a warm layer aloft and falls into a cold air layer below. If
the cold layer is deep enough, then the raindrops freeze. If the cold layer is very dry,
sleet will more readily form due to evaporative cooling.
Snow
A snow storm is usually the result of the warm air associated with an extratropical
cyclone flowing up and over the cold air surrounding part of the cyclone. The air being
lifted, combined with the abundant water vapor available in the warm air mass, causes
cloud water to keep forming. This cloud water is collected by falling ice particles, which
grow as the super-cooled cloud water freezes. The ice particles in the clouds grow and
combine to become so large that upward flowing air updrafts in the clouds can no
longer support them, and they fall to the ground. The more water vapor there is
available to the cloud, and the stronger the updrafts that cause this water vapor to
condense into cloud water or ice particles, the more likely it is that snow will form within
the cloud. A cold, cloudy day with no snow indicates that there is either not enough
water vapor available to the cloud, or that the rising motion creating the cloud is not
enough to cause snow (or both).
Winter officially begins December 22 this year, although it is not uncommon for the
Cashiers area to receive wintry precipitation as early as Halloween.