The eastern boundary of the High plains is sharply delineated by the escarpment breaks, a natural boundary between the upper shortgrass plains and the mixed grass Rolling Plains , which lie at a lower elevation to the east. The Ogallala Aquifer is a primary source of water for many of the region's municpal and agricultural endeavors. The climate of the High Plains is described as semiarid and continental. It is further classified as a dry steppe with mild winters. Mean annual precipitation ranges from 22 inches in the northeast to less than 14 inches in the southwest.
Most rainfall occurs as a result of thunderstorms during the spring and summer months.
Summer temperatures are hot, with rapid cooling at night. Winters are generally mild, but cold air masses from the north may cause brief periods of colder weather. Variability in temperature and precipitation is common from season to season and from year to year. The North American grasslands began to develop approximately five million years ago under the conditions dictated by a cool, wet climate. However, for the past 12,000 years, these conditions have steadily and progressively shifted to the warmer, drier climate of today.