 Some natural prognostications like these are grounded in truth,
given our current knowledge of meteorology, but others are purely
fiction, according to Jim Angel, state climatologist, of the
Illinois State Water Survey.Short-term weather forecasts based on
nature observations are more likely to be accurate than long-term
seasonal predictions. In fact, there may be some merit to the notion
that bad weather is coming when cattle lie down in the pasture and
birds fly low.
"Many animals have a better sense of hearing and smell than we
do, so when humidity, air pressure and wind direction change right
before a storm, as well as the distant rumble of thunder, some
animals may become restless," Angel said. "They can pick up on
weather changes hours before we can."
Predictions based on the appearance of the sky are thought to be
particularly valuable, since certain clouds are associated with
certain weather conditions, according to Angel. Clouds described as
mare's tails and mackerel scales are very high-level cirrus and
cirrocumulus clouds that can precede an approaching warm front, with
rain not far behind.
Likewise, a halo around the moon is actually the refraction of
moonlight through the ice crystals that make up high-level cirrus
clouds, indicating an approaching low pressure system bringing rain
or snow.
Long-term forecasts, such as winter weather predictions, are much
more uncertain.
"Centuries ago, it was important to determine how severe the
winter would be so that adequate wood and supplies would be stored
for the duration," Angel said. "The early settlers' lives may have
depended on their predictions, so they were grasping at anything to
forecast the coming weather. However, the size of the brown band on
woolly worms, the groundhog seeing its shadow or spoon-shaped
persimmon seeds are just happenstance."
Even with today's modern technology, the theoretical limit of
daily weather forecasts is about two weeks. Within the six- to
14-day range, forecast errors can be large enough to limit their
usefulness.
That is why forecasters typically discuss only general patterns
of weather behavior beyond five days, usually in terms of
probability or odds. For example, the eight- to 14-day forecast may
show the eastern U.S. with an increased chance of below-normal
temperatures.
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The same is true for seasonal forecasts, which are driven by both
long-term trends and specific weather patterns such as El Niņo.
For the upcoming winter, forecasters look at historical records
to decipher a pattern. The Midwest is under the La Niņa effect,
which is characterized by unusually cold waters in the eastern
tropical Pacific Ocean.
The National Weather Service's winter forecast for Illinois is an
increased chance for above-normal temperatures in the southern
two-thirds of Illinois, and equal chances of above-, below- and
normal temperatures in the northern third of Illinois. All of
Illinois has an increased chance of above-normal precipitation.
What does the woolly worm predict?
___
The Illinois State Water Survey, at the University of Illinois at
Urbana-Champaign, is a division of the Institute of Natural Resource
Sustainability and is the primary agency in Illinois concerned with
water and atmospheric resources.
[Text from file received from
the Illinois
State Water Survey]
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