Backstepping Storms |
 Dave Thurlow, Host |
Some things we all take for granted. The sun comes up in the east. Here in the U.S., people drive on the right-hand side of the road. And weather systems move from west to east. Hi, I'm Dave Thurlow and this is The Weather Notebook.
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| March 11, 1999 WSI Corp |
Every so often, a low-pressure trough - a kink or dip in the jet stream - will move toward the west, even as the air inside it continues flowing to the east. A meteorologist named Carl-Gustav Rossby discovered years ago that troughs naturally tend to move more slowly than the air inside them. An average trough moves at half the speed of the jet stream. The smaller and more tightly packed troughs are, the faster they tend to move. Conversely, the larger and more distinct troughs often move slowly or even drift backwards, or to the west.
You can find a different kind of backward motion if you look at small-scale weather. Sometimes a thunderstorm will develop on its west flank so quickly that it appears to be moving that way, even though the whole complex might be drifting east. Picture a traffic jam that works its way backwards even as the care are inching forward. Whether it's cars or clouds, you know things will go the right direction eventually--you just don't know when.
For a satellite image of a retrograde storm, visit our website at weathernotebook.org. Our show is underwritten by Subaru, the beauty of all wheel drive with major support provided by the National Science Foundation.
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