Greeley lies within an arid swath of land in the rainshadow of the Rocky Mountains. On average, Greeley receives the liquid equivalent of approximately 13 inches of precipitation each year, although in recent years the actual totals have been lower due to a widespread drought affecting the western United States. Precipitation is generally in the form of rain from May to September and snow from November to March, although snow has been witnessed in recent years as late as May 21 (2001) and as early as September 10 (1993). The snowiest month in Greeley is usually March, but the heaviest single-storm snowfalls occur in the autumn months. Greeley residents can expect a two-foot snowstorm approximately once every 10 to 15 years, with the most recent occurring in December of 2006.
In spite of its aridity, Greeley was awarded Tree City USA designation by the National Arbor Day Foundation in 1980, and many of its streets are lined with large trees. This was originally made possible by Greeley's extensive irrigation system; very few trees are actually native to the area. Some fruit trees can be grown, although their use is usually ornamental. Some of these include apples, pears (especially callery pears), several varieties of plums, and sour cherries.