Mt. Redoubt is beginning to wake-up in Alaska. According to the Alaska Volcano Observatory the current Volcano Alert Level is "Watch" and the Aviation Color Code is "Orange".
According to their Friday afternoon update, "Unrest at Redoubt Volcano continues, though no eruption has yet occurred. Seismicity levels have increased since yesterday evening and have also risen markedly over the last hour."
You can take a look at Mt. Redoubt on two webcams setup by the AVO.
Mt. Redoubt is located 110 miles southwest of Anchorage, Alaska.
According to Wikipedia, Mt. Redoubt erupted in 1902, 1966, and 1989. The eruption in 1989 threw volcanic ash to a height of 45,000 feet. (The attached pictures are from the 1989 eruption.)
If the volcano erupts, it will send volcanic ash high in the sky threatening airliners, but it will also send volcanic ash hundreds of miles (if not thousands) downwind.