One of the tricky things about forecasting weather in Colorado is the terrain and how it affects the weather. With so many different geographical regions across the state, it can get confusing very quickly as to where certain features are and how they affect the weather. This is more typical in the snow seasons where winter storms often are heavily terrain-driven and can make the difference in where snow falls.
Below are detailed descriptions of the various major terrain features of Colorado.
MOUNTAINS -- In general, locations above 9,000 feet in elevation are considered to be the mountains. There are some cities below that elevation that are still considered to be in the mountains due to surrounding terrain. (I.e. Aspen, Steamboat Springs, Durango)
FOOTHILLS -- The foothills are locations between 6,000 and 9,000 feet that parallel a mountain chain. During localized weather events, the foothills west of Denver may be divided into the northern and southern Front Range foothills, with Interstate 70 as the dividing line. Cities and towns in the foothills include Evergreen, Conifer, Pine, Bailey, Georgetown, Idaho Springs, Estes Park, Nederland, Red Feather Lakes, Central City and Blackhawk. There are also foothills in southern Colorado west of Pueblo, Trinidad and Colorado Springs.
NOTE: While some of the southern suburbs of Denver have areas that exceed 6,000 feet in elevation, and can have weather similar to the foothills due to the terrain enhancing precipitation -- they are not technically considered to be in the foothills.
EASTERN PLAINS -- Sometimes just called the plains, this general term refers to most all areas east of Interstate 25 in Colorado. In general, this refers to locations below 6,000 feet in elevation. It includes cities and town like Greeley, Sterling, Akron, Yuma, Wray, Bennett, Byers, Limon, Burlington, Lamar, Springfield, and La Junta. There are a handful of other geographic areas often mentioned during a weather forecast, including Western Slope, Front Range, Palmer Divide, and the Denver metro area.
WESTERN SLOPE -- The area of western Colorado outside of the mountains, generally in elevations below about 7,000 feet are considered to be the Western Slope. Western Colorado doesn't really have any foothills like the eastern slope of the Rockies. Outside of the mountains, the terrain is made up of numerous mesas and plateaus. Cities and towns identified as being on the Western Slope include Grand Junction, Delta, Montrose, Meeker, Craig and Rangely.
FRONT RANGE -- This is technically the front mountain range, or the eastern most range, of the Rocky Mountains. Because you have this mountain range, the foothills, and locations along the Interstate 25 corridor all within about 50 to 75 miles -- the entire area is often collectively termed the Front Range. It may be helpful to picture everything from just east of the Continental Divide to Interstate 25 as the Front Range. This includes cities of Denver and most of its suburbs, Ft. Collins, Colorado Springs, and Pueblo.
PALMER DIVIDE -- The ridge of land that extends from the Front Range of the Rockies in central Colorado, eastward toward the city of Limon It sits right in between the cities of Denver and Colorado Springs. The elevation of the Palmer Divide runs roughly between 6,000 and 7,500 feet, peaking at Monument Hill. This terrain feature is the cause of several small scale, or microscale weather patterns, and can make a world of difference in the weather between Denver and Colorado Springs. Although this elevation technically makes it qualify for the foothills category, it does not parallel a mountain chain like the foothills do. The Palmer Divide is perpendicular to the mountains. Due to the orientation of the Palmer Divide with respect to the eastern plains, the weather can be similar to the foothills during active weather with enhanced precipitation, especially during snowstorms. Cities and towns within the Palmer Divide include Castle Rock, Franktown, Elizabeth, Kiowa, Monument, Black Forest, Sedalia and Palmer Lake. Areas of the Denver metro along C-470 from Chatfield to Interstate 25, and along E-470 from Interstate 25 to Smoky Hill Road are on the extreme northern fringe of the Palmer Divide. Interestingly enough, Limon sits on the eastern fringe of the divide, at an elevation higher than Denver.
DENVER METRO AREA -- This term includes the 8 counties that make up the metropolitan area. (Denver, Boulder, Jefferson, Arapahoe, Adams, Broomfield, Douglas and Elbert) These counties encompass portions of the plains, the foothills and the Palmer Divide -- hence the reason precipitation from storm events, particularly snow, can vary so much in a relatively short distance.
You may have noticed that we defined the foothills as being elevations between 6,000 and 9,000 feet and the plains as areas east of Interstate 25. So what about the small strip of land east of the foothills but west of Interstate 25? (Such as Boulder, Longmont, Lakewood, Arvada, Wheat Ridge, Loveland, Fort Collins, Golden and Highlands Ranch) These areas can go either way, foothills or plains, but in general, tend to have climate characteristics closer to the foothills, especially when it comes to wind.