The road over Siskiyou Summit is typically closed to traffic for many days during winter due to severe weather conditions. At times, it can be closed during winter even when the weather is fine. Regardless, weather data is important to those involved in transportation over the summit. Average monthly temperatures and rainfall are given in the table below. Snow generally falls during the months of November through April, typically peaking with four such days in December. The wind speed over the course of a year varies from an average of in May to episodes of . The average number of rainy days per month varies from 11 in December to only two in June, August and September.