What are the impacts of sublimation on an annual mountain snowpack?
I looked into this and found Sublimation from a seasonal snowpack at a continental, mid-latitude apline site by Eran Hood, Mark Williams, and Don Cline go into great detail on this subject. 


Martinelli (1960) reports that sublimation is
responsible for only 1-2% of summer snowpack ablation in snowfields between 3500-3800 m in the Rocky
Mountains.
(West and Knoerr, 1959) Measurements from snow evaporation pans at the Central Sierra Snow Laboratory in
California measured annual sublimation at only 25-35 mm or 2-3% of total ablation over the snow season
Beaty (1975) reported that sublimation was responsible for 80%
of the ablation of fresh snow and 60% of the ablation of older snow during springtime conditions in the
White Mountains of California.
Kattelmann and Elder
(1991) estimated sublimation from snow to be 18% of total precipitation over two water years based on data
collected in the Emerald Lake Basin in the Sierra Nevada.
Marks and Dozier snowpack estimated lost to sublimation in the Sierra Nevada to be
20%. 
Water losses to sublimation were equal to 13% of annual
precipitation at Niwot Ridge.
Hood, Willians &amp; Cline report 15% of maximum snow accumulation at the study site was lost due to sublimation.
Another article notes the importance of vegetation on sublimation:   ranging from 13% for a mixed spruce–aspen, 31% for the mature pine and 40% for a mature spruce stand. The results indicate that sublimation can be a significant abstraction of water from mature evergreen stands in northern forests.


The results seem somewhat inconclusive.  This topic needs more comprehensive and robust research.

Take-aways


15-20% is the range given by the most recent studies in the intermountain USA.
Solar
radiation was the most closely correlated with trends in sublimation and condensation.
Vegetation impacts sublimation rates.