Montana Average March Temperature
Analysis based on data from the PRISM Group at Oregon State University, which provides quality-controlled temperature and other climate data. The PRISM Group divides the lower 48 states into small squares roughly 2.5 miles on a side, and uses weather station records to compute one temperature value per square, generating a complete and highly detailed map. (The PRISM Group uses a sophisticated method of interpolation to do this, incorporating three dimensional terrain details and additional factors.) The underlying dataset is based on records from weather stations belonging to the Cooperative Network of NOAA National Climatic Data Center; for reference, there are currently 696 such stations in Montana.
For this graph, we averaged average March temperatures for all PRISM Group-generated squares in Montana in each year to get one statewide average March temperature per year. Next, we “smoothed” these statewide averages by performing a “5-year running average” for each year. What this means is that for a given year—say 2007—the temperatures for that year and the four preceding years were averaged together. This well-established method allows easier visual detection of long-term trends in data that naturally vary a lot from year to year.
For the data displayed here, there is a statistically significant upward trend (confidence level > 99%), with an increase of 7.6°F from 1950 to 2007, which is somewhat higher than the 5 to 7°F increasereported by Prof. Steve Running, of the University of Montana, based on a smaller number of weather stations across Montana (see slide 2). We conducted this statistical analysis prior to taking the 5-year running averages displayed in this graph. The Montana State Climate Office is a resource for further interpretation of temperature and climatological records for Montana.