<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> <P> In most mountain areas in Oregon, the ground above 4,500 feet (1,400 m) is covered with snow from December through April . Snow depths, which vary with elevation and time of year, average an estimated 50 to 100 inches (130 to 250 cm) in the Cascades and 25 to 65 inches (64 to 165 cm) in the Blue Mountains at the end of January; by the end of April, they diminish to 40 to 120 inches (100 to 300 cm) in the Cascades and 5 to 45 inches (13 to 114 cm) in the Blues . Glaciers remain year - round on some Cascade peaks higher than 7,000 feet (2,100 m) above sea level . </P>

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