Medford sits in a rain shadow between the Cascade Range and Siskiyou Mountains called the Rogue Valley. As such, most of the rain associated with the Pacific Northwest and Oregon in particular skips Medford, making it drier and sunnier than the Willamette Valley. Medford's climate is considerably warmer, both in summer and winter, than its latitude would suggest, with a Mediterranean climate (Köppen "Csa"). Summers are akin to Eastern Oregon, and winters resemble the coast. Here, summer sees an average of 57 afternoons over and eleven afternoons over . In August 1981, the high temperature reached over for four consecutive days, with two days reaching . Freezing temperatures occur on 69 mornings during an average year, and in some years there may be a day or two where the high stays at or below freezing; the average window for freezing temperatures is October 23 through April 23. The city is located in USDA hardiness zone 8. Medford also experiences temperature inversions in the winter which during its lumber mill days produced fog so thick that visibility could be reduced to less than five feet. These inversions can last for weeks; some suggest this is because the metropolitan area has one of the lowest average wind speeds of all American metropolitan areas. The heavy fog returns nearly every winter with the inversions lowering air quality for several months without relief.