Proximity to Mountains

The mountains have a huge impact on the climate of Colorado. With elevations ranging from below 7,000ft in the lower mountain valleys to over 14,000ft on the highest peaks these dramatic changes in elevation affect the temperature, humidity, precipitation, and wind. Temperature decreases with elevation. In the summer, temperatures typically decrease by about 4-5F per 1,000ft. On a typical July afternoon, the valley temperatures can range from 70-80 F but the higher mountains are 50-60F at the same time. 

Air currents reach Colorado from the westerly direction. Storms traveling from the Pacific Ocean lose much of their moisture falling as rain and snow on the mountaintops and the westward-facing slopes. As a result, precipitation is light in the lower elevations. And eastern slope areas receive relatively small amounts of precipitation from storms, especially in winter. 

The plains sit on the Eastern side of the Colorado Rocky Mountains. The air that moves across Colorado from West to East travels up and over the mountains. The mountains create the orographic effect. This means that the plains sit in the "rain shadow" of the Rockies.

As you leave the Front Range and enter the Rockies the elevations rise abruptly to 7,000 to 9,000 feet. Backing these “foothills” the mountain ranges rise to 9,000 feet with the highest peaks rising over 14,000 feet. Thunderstorms are prevalent during spring and summer, when there is more moisture in the atmosphere, and can be quite severe. This time of year, the hail damage to farmers' crops can be devastating. This region averages 6 or more hail days per year. Tornadoes are also quite common. In most years at least 40 tornadoes are confirmed but most are small and short-lived. 

Average annual precipitation in eastern Colorado is between ten and twenty inches. The wettest areas are on the northeastern plains near the Colorado-Kansas or Colorado-Nebraska borders-areas furthest from the mountains. Most of this precipitation falls in the form of widespread soaking rains in April through early June or as intense bursts from thunderstorms in June through August.  

Air that moves from West to East across Colorado is forced high into the atmosphere by the high altitudes of the mountains. The air is affected by the orographic effect. This means that when the air is forced up and over the high altitude mountains, clouds will form and lead to more precipitation in the mountains compared to the lowland Eastern Plains and the Western Slope.

Temperature inversions are common in the mountains where the cold air is more dense and so it settles in the valleys at night. This leaves the valleys cooler than the mountain tops at night and in the early morning. During winter subzero temperatures are common, reaching as low as -30F some nights.

Winds often blow up the valleys from lower to higher elevations during the day as the valley’s air heats and rises. At night the wind directions shift as the more dense cold air sinks and creates winds that blow from high elevation to the lower elevations.

Mountain peaks and ranges are effective thunderstorm generators. Some years, thunderstorms form nearly every afternoon. These thunderstorms are most common in late July and throughout August. Snow and hail are possible from mountain storms even in the hottest months of the summer.

Occasionally, strong northerly winds carry moist air from the Gulf of Mexico which interact with the colder polar air that can produce heavy snowfall. Heavy snowfall on steep mountain slopes can create avalanche conditions which pose serious threats to winter skiers, hikers, and road maintenance crews. Strong winds are common at elevations above treeline (~11,500ft.). During the winter these winds can exceed 50 to 100mph! But tornadoes are very rare. Yet lightning is quite common and one of the greatest hazards in the mountains. The most common areas for lightning strikes are above treeline in the mountains which can cause injury to stranded hikers and can even start wildfires. 

Since the air moves from West to East across Colorado, the high elevations of Colorado do not impact the weather on the Western Slope as much as it does in the interior and eastern slope of the mountains. Since the western slope slowly decreases in elevation as you enter Utah, there are no impacts from mountains to the West of the Western Slope. 

Air moves across Colorado from West to East. Since there is very little moisture further West of the Colorado border, there is very little moisture in the air that travels over the Western Slope. As that air moves further East it gains moisture and any moisture in the air is wrung out by the mountains. Since there is very little moisture in the air, the moisture that falls on the mountains stays in the mountains and the Western Slope stays generally dry. And since there is little moisture, there are very few cloudy days on the Western Slope.

The elevation of the Western Slope gently rises to the higher mountain elevations. Therefore the orographic (mountain rain shadow) effect does not force water out of the clouds until the air passes the Western Slope and starts to enter the mountain region where there are more dramatic changes in elevation.

Precipitation is more evenly distributed throughout the 12 months of the year compared to the eastern plains but most of the precipitation occurs in the winter months and June is the driest. Each year there is an average of 8-14 inches of precipitation but it is still possible for flood-producing storms to form. But severe weather doesn’t usually include hail or tornadoes.