March in Montana has warmed sharply since 1950

Rising temperatures can affect climate generally, but increases at specific times of year can have special impact. In the Northern Rockies, temperatures have been rising especially fast in springtime — a trend that is projected to continue. Warm springs leads to earlier melting of winter snowpack which leads to reduced stream flow and more extensive wildfires.

Analysis by Climate Central scientists, based on data from 696 weather stations across Montana, shows that temperatures rose 7.6°F from 1950 to 2007. An older look by the Montana State Climate Office, based on a much smaller number of stations, pegs the increase at 5-7°F since the 1950s.[[Running, Steven W. “Annual Mean Temperature,°F 1951-2004.”]]

Climate Central ran its analysis by using data from the PRISM Group at Oregon State University, which generates high-quality temperature and other climate data. PRISM divides the lower 48 states into small square cells, roughly 2.5 miles on a side, and uses weather station records to compute a single average temperature value per square per day or month. PRISM uses only stations belonging to the Cooperative Network of NOAA National Climatic Data Center (there are currently 696 in Montana).[[When there is no station inside a cell, PRISM estimates what the temperature value should have been, based on values from nearby stations, the local terrain, and well-tested statistical methods.]]

Climate Central scientists took the average March temperatures for all the squares in Montana to get one statewide average March temperature per year. Next, they “smoothed” these statewide averages by performinga “five-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 makes it easier to see long-term trends in data that naturally vary a lot from year to year.