Blame Weather on the Jet Stream Pattern
By Tracy Sayler, Communications Specialist; Minnesota Assn. of Wheat Growers, Minnesota Wheat Council
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Prairie Grains is the
official publication of
the Minnesota
Association of
Wheat Growers,
North Dakota Grain
Growers Association,
South Dakota Wheat,
Inc., and the
Minnesota Barley
Growers Association.
The jet stream is an upper air movement that serves as a path for thunderstorms, Osborne explains. Usually, the jet stream pattern fluctuates and thunderstorms occur throughout the Plains more evenly. However, the 1991 volcanic eruption of Mount Pinatubo in the Philippines dramatically altered atmospheric pressure and weather patterns, even in the United States. The atmospheric disturbance carried into the summer of 1993.
"The jet stream became locked in place, resulting in storms passing over the same location day after day in the Midwest," Osborne says.
This past summer the situation repeated itself, only not as intensely nor as widespread. Osborne says there are signs the jet stream is returning to a "less confined orientation," although a wetter-than-normal pattern still exists.
COULD RAIN BE DIVERTED BY CLOUD SEEDING?
Precipitation results when water vapor in a cloud cools and accumulates as ice crystals, which then fall into warmer air as rain. With cloud seeding, nucleating agents such as dry ice or silver iodide are injected into a cloud, to convert water vapor into ice crystals that will grow larger and finally fall through the cloud base as rain.
Cloud seeding is usually referred to as a means of increasing the likelihood of precipitation in an area. However, could clouds be seeded to strategically carry precipitation away from an already water-soaked area?
On a small, short-lived thunderstorm in about a 25-mile radius, possibly, says Osborne. Indeed, cloud seeding has been tried to a limited degree as a means of hail suppression.
However, thunderstorms in the general weather pattern in force the past two summers would have been too massive to influence by cloud seeding, he says.
The effect of cloud seeding lasts only about 30 minutes, he says, and the amount of precipitation affected by cloud seeding is not substantial. "It can be measured in terms of only a few tenths of an inch," says Osborne.