Dear Seema,

One possible cause is winter drying.  Each winter, drying of conifers such as juniper is a common injury caused by weather. Damage typically occurs during late winter to early spring. It is caused by warm, dry winds during times when the tree’s root system is still frozen. Conifers transpire through their needle during winter resulting in some water loss. Periods of warm, dry winds accelerate the water loss, which the frozen roots are unable to replenish. This causes the needles to dry and become discolored. Also, with winter drying, often the bases of the needles and at least some entire needles remain green. 

In many cases, the damage is minor and, with the exception of loss of some needles, trees recover. More severe damage can result in death of branch tips or entire branches. The buds on the tips of branches are likely viable and the tree may push new growth.

It is important in Colorado to provide winter watering. Here is some information about providing water to trees and shrubs during the winter.  https://planttalk.colostate.edu/topics/trees-shrubs-vines/1706-fall-winter-watering/

Junipers do not like heavy pruning. It may not be necessary to prune it. You can lightly prune out some of the brown parts if you can still avoid cutting out the green parts.

Thank you for your inquiry and best of luck with your juniper.