This post refers to my analysis of recorded monthly mean temperature trends at Morris, Minnesota, USA. The station is located near a small rural town and has temperature records since 1886. The analysis used raw data (as recorded, without any adjustments) as published by KNMI (the Dutch Meteorological Institute). Polynomial curves of best fit were added to the plots.
The Morris station (Morris WC Experiment Station, WC = West Central) is at an elevation of 348m near the town of Morris in the central west of Minnesota state. Records commenced in January 1886 at a school run by the Sisters of Mercy, and since 1910 the station has been operated by the University of Minnesota.
Over the period Jan 1886 – Dec 2016 (a period of 131 years) there are only 11 months of missing data. The years are 97% complete.
Morris has a highly variable climate typical of the upper mid-west of USA. Winters are severe but the summers are warm. Mean monthly temperatures vary from -13.0 degC (in January) to +21.6 degC (in July). Extreme monthly mean temperatures recorded are -22.7 degC (in January 1887) to +25.6 degC (in July 1936).
Mean, Maximum and Minimum Monthly Temperatures
Plots are shown below for annual mean temperature and the monthly mean temperature for each of the 12 months. A polynomial trendline was fitted to each graph. A comparison of the monthy trendlines are also presented. It should be noted that the trendlines (in red) can sometimes be misleading at either end of the series as the line is very dependent on the temperature values in individual years (this sensitivity does not occur away from the start and end of the series).
Annual Mean Temperatures
Monthly Mean Temperature Trendlines
- The plots generally show cyclical monthly trendlines with peaks around 1930 and 2010(?) and troughs around 1890(?) and 1970, a cycle period of about 80 years.
- The peak monthly trendlines around 1930 are generally greater or of similar magnitude to those around 2010.
- A peak or plateau in the trendline around 2010 is observed to occur in most months.
- The average temperature trends since 1886 are about zero (-0.25 degC/century for trend peaks and +0.25 degC/century for trend troughs).
- There are no alarming increases in the temperature trendlines in recent decades.
Morris is one of 257 stations, worldwide, for which I have analysed long-term temperature trends. The analyses at 50 representative stations are summarised in the blog post: world-50-temperatures
Please let me know what you think of my analyses. firstname.lastname@example.org
This article was written by Brian Gunter of Narooma, NSW, Australia. In his previous life Brian was an engineering hydrologist involved over many years in the analysis of rainfall and river flow data for the planning of water resources projects in Australia, Asia and Africa. In recent years he has been one of the Marine Rescue NSW (previously Royal Volunteer Coastal Patrol) volunteer weather observers who operate the Narooma station for the Australian Bureau of Meteorology.