21.   Clouds will thicken near the Northwest coast as a vigorous Pacific low pressure area approaches.

22.   Cold air will spread south tonight in the wake of the low pressure area.

23.   Farther north, a cluster of showers and thunderstorms will surround a weak low pressure area moving east along a stationary front draped across the Middle Atlantic States.

24.   Forecasters along the East Coast are concerned on Sunday about a strengthening low pressure area while a Pacific storm weakens as it approaches the West Coast of North America.

25.   High pressure areas are masses of sinking air that warm through compression during descent.

26.   High pressure areas are zones of sinking air.

27.   Hot conditions with abundant sunshine will spread from the interior West into the western Plains as an enormous high pressure area over Utah strengthens.

28.   In addition to the stifling temperatures it brings, the high pressure area diverts weather fronts that trigger cooling thunderstorms.

29.   It passed without incident, but began to intensify rapidly as it encountered the edge of an unusually intense high pressure area over southeastern Canada.

30.   Light snow will surround a low pressure area as it moves across the upper Midwest on Sunday.