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[August 05, 2009] (AP) The large low pressure system over eastern Canada along with its cold front extending southwestward across the Great Lakes, Ohio Valley and central Great Plains were forecast to be the focus for active weather Wednesday as it progresses eastward and southward.

Rain and thunderstorms were expected ahead of the frontal system across much of the eastern and southern parts of the nation. Strong to severe thunderstorms were possible over parts of southern New England to southern Maine during the late afternoon and early evening hours.

Meanwhile, the southern portion of the front was to become near stationary across the central Plains on Wednesday, generating numerous showers and thunderstorms. In particular, a risk of severe thunderstorms was expected from the central Plains to lower and mid-Mississippi valleys. Some storms were expected to possibly produce damaging winds and severe hail. Apart from the active weather, this cold front was to also usher in cooler air from Canada, bringing a decrease in temperatures across the eastern Great Lakes, Northeast and the Mid-Atlantic.

Moving to the west, a major change in weather pattern was anticipated Wednesday and Thursday as the low pressure system off the coast of northern California finally moves ashore. The strong ridge of high pressure across the West, responsible for the recent record-breaking heat over the Pacific Northwest, was expected to break down, followed by cooler temperatures and increasing threat of showers and thunderstorms Wednesday through the weekend.

Precipitation was expected from the Rockies to the Pacific Coast. In addition, monsoonal moisture was to continue to stream northward through the Four Corners and Rockies, initiating widely scattered showers and thunderstorms.

Elsewhere, a stationary front over the northern high Plains and Rockies was to aid in producing moderate to strong thunderstorms. Hail and strong wind gusts were possible Wednesday afternoon and night. Moreover, sea breezes would continue to trigger widely scattered thunderstorms along much of the southeastern coast.

Temperatures in the Lower 48 states Tuesday ranged from a low of 36 degrees at Embarrass, Minn., to a high of 117 degrees at Death Valley, Calif.

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On the Net:

Weather Underground: http://www.wunderground.com/

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http://iwin.nws.noaa.gov/

Intellicast:
http://www.intellicast.com/

[Associated Press article from Weather Underground]