Most of the precipitation reaching this vicinity results from strong invasions of moist air from the North Pacific source region. Greatest amounts of both rain and snow occur when this moist air is overrunning a weak front that has become stationary along an east-west line a short distance south of the area. Many winters have gone by without a temperature of zero being recorded in the valley, but the prairie sections usually experience lower temperatures. The summers experience hot and dry periods with as many as 10 consecutive days with afternoon temperatures reaching 100 degrees or more. Considerable cooling after sunset makes the nights very comfortable.
Cold waves occur when arctic air, originating in the Yukon Territory, moves southward.
Such cold waves are relatively infrequent when compared to the number of arctic outbreaks east of the continental divide in Montana only a short distance away. Winds are lights, usually prevailing from the east, with occasional stronger winds accompanying the well-developed frontal systems from the west. Relative humidity averages about 70 percent during the winter months and gradually lowers to about 40 percent during July and August. The growing season of approximately 200 days in this part of the country, makes conditions favorable for the growing of many types of fruits, vegetables, and berries.