Montana Electronic Precipitation Map

Scientific Disciplines
Physical Sciences
universal kriging
precipitation map
Volume 17, No. 1-4

Montana electronic precipitation map
Phillip Farnes, * Snowcap Hydrology, Bozeman Montana 59715,
John Huddleston, Geophysical Computing Solutions, Livermore, Colorado,
Kyle Flynn, Montana Department of Environmental Quality, Helena, Montana 59620, kflynn@
A new average annual precipitation map (AAP) has been developed for Montana using 
GIS techniques including universal Kriging and elevation dependent linear regression. The 
map can be updated with new base periods or used for different parameters. The current map 

uses the 1981-2010 AAP base period and universal Kriging. Results were compared to hand-
drawn maps to assure appropriate location of isohyets. Stations adjacent to Montana in Idaho, 
Wyoming, North Dakota, South Dakota, Alberta, and British Columbia were used to assure 
compatibility along the border and provide the capability to develop a comparable map for 
drainages flowing into Montana. Isohyetal lines were set at 2-in increments < 20 in AAP and 
10-in increments > 20 in. Approximately 1400 stations were used for analysis of which ~ 1100 
were in Montana and 300 in areas adjacent to Montana. AAP was estimated at snow courses 
using correlation between April 1 snow water equivalent and AAP from SNOTEL stations 
in their area. NWS Climatological stations and NRCS SNOTEL stations provided majority 
of locations having current AAP. Data from an old NWS storage precipitation gage network, 
NRCS storage gages, and RAWS stations were also incorporated as well as a few stations 
from individuals, USGS, USDA Forest Service, and others. To assure that precipitation 
at elevations above and below the data sites was applied correctly, synthetic points were 
developed using linear elevation-precipitation relationships from nearby measured sites. Maps 
will be available through Montana DEQ or Montana NRIS web sites electronically.