<P> In the Willamette Valley east of the Coast Range, storms blowing from the Pacific retain enough moisture to drop from 35 to 45 inches (890 to 1,140 mm) annually in the most heavily populated part of the state . East of the valley, the storm air rises again as it meets the Cascade Range, cooling once more and forming condensate at elevations often as low as 3,000 feet (910 m). Since volcanic peaks in the range are quite high--more than 11,000 feet (3,400 m) in the case of Mount Hood--most of the remaining Pacific moisture falls here in the form of rain or snow . </P> <P> The remaining two - thirds of the state is relatively dry, classified as semi-arid, with large areas receiving no more than 12 inches (300 mm) a year . Exceptions occur at higher elevations in the Blue Mountains and the Wallowa Mountains to the northeast, which get 50 to 80 inches (1,300 to 2,000 mm) a year . </P> <P> Across Oregon, the wet season runs from November through March, when the jet stream is strongest in the Northern Hemisphere . Precipitation is less in the months between winter and summer: April through June in the spring and September and October in the fall . Statewide, the dry months are July and August, when moisture arrives during afternoon thunderstorms, mainly in the mountains, and less often from storms that reach the north coast and adjacent counties . </P> <P> Snowfall in Oregon is greatest in the Cascade Range . Based on data from ski resorts and a few official weather stations, average annual snowfall in the Cascades can range from 300 to 550 inches (760 to 1,400 cm). The state's largest annual snowfall on record, 903 inches (2,290 cm), occurred at Crater Lake in the Cascades in 1950 . In the Blue Mountains of eastern Oregon, snowfall totals can also be large, between 150 and 300 inches (380 and 760 cm). On the other hand, most winter precipitation in the Coast Range falls as rain, though heavy snow sometimes occurs . </P>

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