11.   But in winter, potent weather systems draw Arctic air south, while currents of warm air stream north.

12.   Clouds will continue to shroud the Gulf Coast states Tuesday as a broad, uninterrupted flow of moist air streams northward from the Gulf of Mexico.

13.   Clusters of thunderstorms will erupt in the Plains from Texas to the western Great Lakes as a corridor of steamy air streams toward Canada.

14.   Farther east, showers and thunderstorms will fall in from the Tennessee Valley to the southern Great Lakes as humid air streams northward from the Gulf of Mexico.

15.   Humidity will also soar as tropical air streams northward from the Gulf of Mexico.

16.   Invisible swirling air streams resembling horizontal tornadoes trail from each wingtip, enlarging, dissipating and falling with time.

17.   Locally heavy bands of snow will develop south and east of the Great Lakes Tuesday as chilly air streams southward.

18.   Low clouds will cover much of the interior Northeast on Wednesday as cold air streams over the Great Lakes, whose waters are still warm.

19.   Meanwhile, showers will continue in the highlands of the interior West as moist air streams north from the Gulf of California.

20.   More locally, heavy rain is expected across western parts of Washington and Oregon as mild, moist air streams inland from the Pacific.