Mean annual precipitation and variability in Idaho

TitleMean annual precipitation and variability in Idaho
Publication TypeConference Proceedings
Year of Conference1994
AuthorsMolnau, M., and Newton C.
Conference Name62nd Annual Western Snow Conference
Series TitleProceedings of the 62nd Annual Western Snow Conference
Date PublishedApril 1994
PublisherWestern Snow Conference
Conference LocationSante Fe, New Mexico
KeywordsEstimating precipitation, Isohyetal maps, Isohytes, Precipitation, Variability

The mean annual precipitation and its variation in time and space are required for many design procedures. A map showing the isohyetal lines of mean annual precipitation for 1961-90 in Idaho was prepared using data from a wide range of sources. A total of 278 precipitation stations with measured data were used together with estimates made at 130 snow courses. Estimates were made for many areas using local expertise and local elevation-precipitation-aspect relationships.The monthly precipitation was derived using regionalized curves of percent of annual precipitation that falls in any month. The monthly precipitation is found by using the mean annual precipitation and multiplying by the appropriate regional curve.The percent of the mean annual precipitation that falls in the winter six months can also be regionalized. On average, approximately 60 percent of the annual precipitation falls during October-March. This ranges from a low of 54 percent in the Bear River basin to 66 percent in the Middle Snake and Panhandle basins.The corfficient of variation of the mean annual precipitation ranges from 15 to 30 percent. This plots as a relatively smooth contour with the highest value in the Bear River basin (30 percent) and the lowest in the Clearwater and Panhandle basins (18 percent).