Montana Earth Science Picture of the Week

During World War II, Japan released 9,300 balloon bombs that were intended to be carried to the United States by a high altitude wind known today as the "jet stream". Less than 400 of the bombs are known to have made the 6,000-mile journey. At least 35 of these bombs are known to have landed in Montana. At the start of the balloon-bomb program, which ran from November 1944 to April 1945, Americans were still unaware of Jet Streams. However Japan realized that these winds could transport the bomb-carrying balloons to the United States within days. Although the position and speed of the jet stream is variable, in the winter it often streaks across the Pacific from Japan to the United States. When inflated with hydrogen, each 33-ft. wide balloon could carry up to 794 lbs. of ballast and bombs. As they floated upward to a height of 4-8 miles they were taken into the jet stream and carried at speeds of up to 200 miles per hour toward the U.S.A. Little was known about the jet stream during WWII, but today meteorologists recognize the significance of these high altitude, high speed winds. Here are some jet stream facts.

1. There are other jet streams besides the one that carried balloon bombs across the Pacific. That one, the same one that often blows over Montana, is called the sub-polar jet stream.

2. One of the most important aspects of the jet streams is that they influence the path of storms. Knowing where a jet stream is can help meteorologists predict the path of storms.

3. The first American to experience jet streams were crew members of the B-29 airplanes that bombed Japan during November 1944. These men were first to experience the winds because their airplanes could fly higher than the older B-17s.

4. The sub-polar jet stream typically marks the boundary between warmer air to the south and colder air to the north. In the summer of 1993, the jet stream stayed farther south than usual. This was an unseasonably cold, wet summer in Montana, and included historic flooding in the Midwest and snow in Butte, Montana on the 4th of July.

5. Twice daily (4 am and 4 pm MST) weather balloons (no bombs) are launched simultaneously from hundreds of sites including Great Falls and Glasgow in Montana. This effort lets the National Weather Service monitor the position and speed of the jet streams, and shows them how it has changed over the past 12 hours.

Article in Montana, The Magazine of Western History . . .
The Winter 2002 issue of this magazine features an article about the balloon bombs. The article, which was written by Larry Tanglen, includes the map shown above, as well as a photo and other graphics. This magazine is a publication of the Montana Historical Society

Term: jet stream