When will the 1st fall frost arrive in Illinois?
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[October 11, 2013]
CHAMPAIGN -- While the actual
date varies from year to year, Illinois farmers, landscapers and
gardeners anticipate the first fall frost in October, and it’s a
sure sign that the growing season has ended.
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Frost is caused by the formation of thin ice crystals on the ground
or other surfaces in the form of scales, needles, feathers or fans,
according to Jim Angel, state climatologist, of the Illinois State
Water Survey, University of Illinois. If a frost period is severe
enough to end the growing season or delay its beginning, it is
referred to as a "killing frost." Although 32 degrees F is used to
identify frost, visible frost can be seen on the ground and on
objects when the reported temperatures are slightly above 32
degrees. On calm, clear nights, the cold, dense air collects near
the ground. Under these conditions, the temperature near the ground
can be a few degrees cooler than at the 5-foot height of the
official National Weather Service temperature sensors.
While there is an overall pattern of earlier dates in northern
Illinois and later dates southward, sometimes the local conditions,
such as topography, are just as important, Angel says. In general,
many areas in northern Illinois experience the first frost sometime
during Oct. 1-10, while central Illinois’ first frost comes Oct.
11-20, and southern Illinois’ first frost occurs Oct. 21-31.
The actual date varies from year to year. For tender plants,
subtract two weeks from the average date to be on guard against an
early frost.
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Open, grassy areas are usually the first to experience frost,
while areas under trees are more protected. Homeowners can protect
plants by covering them when a frost is expected. Plants near heated
buildings sometimes are spared too. Because of the abundance of warm
buildings and trees, we see frost arrive in town a little later than
in the countryside.
For maps of the first fall frost by location, visit
http://www.isws.illinois.edu/
atmos/statecli/Frost/frost.htm.
[Text from file received from the
Illinois State Water Survey]
The Illinois State Water Survey at the
University of Illinois at Urbana-Champaign, a division of the
Prairie Research Institute, is the primary agency in Illinois
concerned with water and atmospheric resources.
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