Friday, September 25, 2009

Where's the jet stream?

In my last post, I blamed the poor fall migration on the position of the jet stream. Fall migration is best following the passage of a low pressure system/cold front, with winds from the north or northwest. Weather systems in North America generally travel from west to east across the continent, with their route guided by winds aloft -- the jet stream. Thus, a nice dip in the jet stream somewhere in the western Great Lakes is most likely to bring the right kind of conditions for birds to move into our area.

My friend Mike McDowell posted some graphics and a nice explanation on his blog last week. Go take a look! His four-panel image comes from, and is updated at least daily. The direct link to the current jet stream position image is here, and as I write this on Friday afternoon, it looks like this:

At long last, the jet stream is beginning to sag south. Although it isn't in the ideal position (such as the example Mike posted), it should help move birds along.

The California Regional Weather Service has a great web site that has all sorts of jet stream images and forecasts, including loops. Use the North America "latest available" link here for a detailed current map. This link goes to an animated loop of a five-day forecast.

These maps and forecasts should be used in conjunction with radar images. The Wisconsin Society for Ornithology has a tutorial on how to understand radar images and so does New Jersey Audubon.

Here are those handy links again:

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