Low Level Jet
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If you fly regularly across the country or watch weather reports on television, you're no doubt familiar with the jet stream. But you may not know that there's another weather-making wind channel closer to the surface. It's called the low level jet, or LLJ. Hi, I'm Dave Thurlow and this is The Weather Notebook.

Smaller, slower, and more localized than its high-flying cousin, the LLJ is a kind of atmospheric hose that feeds moisture and warm air into rain clouds. Take your average thunderhead boiling up over Kansas on a hot July afternoon, turn on the LLJ, and by nightfall you'll be wading through torrents of rain, maybe even a flash flood. As one research meteorologist puts it, "The low level jet is really efficient at taking moisture from a far away source, like the Gulf of Mexico, and transporting it to a place where you don't usually have it, like the Central Plains."

Recently, the LLJ has been linked to some of the heaviest downpours of the Indian monsoon. Blowing off the eastern hills of Kenya, the LLJ soaks up moisture as it flows northeast over the warm Indian Ocean and then dumps its wet cargo into already saturated monsoon winds. And now field studies suggest that the LLJ may be the secret ingredient that turns mediocre winter storms off the coast of California into major precipitation events that cause floods, mudslides, and road washouts.

Don't underestimate the LLJ. It may be lowly and obscure, but it can pack an extremely wet wallop.

Thanks today to contributing writer, David Laskin, of Seattle, Washington, author of numerous books, including Braving the Elements. For more about David, low level jet streams and The Weather Notebook, check out the website, mountwashington.org. Today's program is supported by the National Science Foundation and Subaru of America.