SkyWatch: Asian typhoon retires in Northwest

If we had a sponsor for this weather column, today’s phrase might go something like this: “Today’s weather is brought to you by Typhoon ­Jangmi.” Why, you ask? Because the rain we get today (and especially tonight) is some of the moisture leftover from the typhoon that recently hit Asia. The moisture is now moving onto the West Coast.

It looks like the heaviest rain will be in Southern Oregon and Northern California, but we should still see our first good soaker of the fall, with lots of showers continuing Saturday. And expect breezy weather at times as changes in the weather kick up some wind.

But how is it, exactly, that part of a storm from near Taiwan can end up over us just days later? Well, you can thank the jet stream for that one. In basic terms, the jet stream is a river of wind in the sky that steers our storms. In this case, the river of wind is ­moving more than 100 miles an hour across the Pacific, carrying some of Asia’s storms with it.

As the Pacific becomes more active and more rain systems start firing up, the jet stream usually shifts its focus. It spends most of fall, winter and spring aimed at Washington & Oregon. This is linked to cooling temperatures in our half of the world. The jet stream forms on border of cold air to its north and warm air to its south. Well, that warm air goes more and more south during winter. So does the jet stream.

I hope you’re enjoying our cool down and our first real shot of fall weather for 2008.

Bruce Sussman is a meteorologist at Portland’s CBS affiliate, KOIN-TV, Channel 6. His column appears on Fridays. Reach him at bsussman@koin.com.