By Seth Borenstein 

WASHINGTON (AP) – Mariners take note: The jet stream is creeping northward and weakening, new research shows. That potentially means less rain in the already dry South and Southwest and more storms in the North.

The jet stream is America's stormy weather maker. And because the jet stream suppresses the formation of hurricanes, the trends could mean more and stronger tropical storms.

From 1979 to 2001, the Northern Hemisphere's jet stream moved northward on average at a rate of about 1.25 miles a year, according to the paper published earlier this month in the journal Geophysical Research Letters. The authors suspect global warming is the cause, but have yet to prove it. They also must do more research to pinpoint specific consequences.

The jet stream is a high-speed, constantly shifting river of air about 30,000 feet above the ground that guides storm systems and cool air around the globe. And when it moves away from a region, high pressure and clear skies predominate.

Climate models have long predicted that with global warming, the world's jet streams would move that way, says Ken Caldeira, a climate scientist at the Carnegie Institution of Washington in Stanford, Calif. However, proving it is a rigorous process, using complex computer models to factor in all sorts of possibilities. That has not been done yet.

A rate of 1.25 miles a year ''doesn't sound like much, but that works out to about 18 feet per day,'' Caldeira says. ''If you think about climate zones shifting northward at this rate, you can imagine squirrels keeping up. But what are oak trees going to do?

The northern jet stream ''is the dominant thing that creates weather systems for the United States,'' Caldeira says. ''Basically look south of where you are and that's probably a good guess of what your weather may be like in a few decades.''