Cytospora is a fungus which can kill limbs on fir trees. In many cases you can observe cankering on affected limbs; I did not observe any such cankers in your photos, but it may be worth doing a little bit of further investigations.
The following links provide some pictures and more information on this pathogen:
Winter Browning: https://planttalk.colostate.edu/topics/weeds-cultural-problems/2114-winter-browning-evergreens/
Winter water can help alleviate drought related problems: https://extension.colostate.edu/topic-areas/yard-garden/fall-and-winter-watering-7-211/