The Natural Observer

The Natural Observer

116 Years of Rain Data

Sunday, August 18, 2013

I have been looking at the rainfall history of Hillsboro (1896 to date) and thought I would share some observations. In addition to the annual figures for those years, I have looked at the July and August totals and the July plus August total. All of this is found below. The raw data I used are from the Western Regional Climate Center. Generally speaking there are some strong cycles in our rainfall pattern.

For July, there are data for 95 years. The maximum rainfall in July was 5.73 inches (1925) and the minimum was .06 inches (1980). The average (simple mean) for July, for these 95 years, is 2.31 inches.

For August, there are data for 99 years. The maximum rainfall in August was 7.93 inches and the minimum was .03 inches. The average (simple mean) for August is 2.4 inches.

For July plus August, there are data for 95 years.The maximum rainfall for these two months was 10.44 inches (1993, but 10.38 inches in 1925). In all there were 7 years (7.5% of the total) where the rainfall exceeded 9 inches. The minimum rainfall during these years, for these two months, was 1.02 inches (2011, but 1.36 inches in 1948). In all there were 27 years during the period when the rainfall was less than 3 inches - almost a third of time. The average (simple mean) rainfall during this period was was 4.7 inches total for the two months.

For the annual rainfall amount, there are data for 96 years. (See notes in the charts below for information about when and why years are left in or out. In 1931 July was missing data, but I left the annual figure in the analysis.) The maximum annual rainfall during this period was 21.59 inches (1905). The minimum rainfall in any year was 3.35 inches (1956). The average (simple mean) was 12 inches. During this period there were three years (3% of all years) where more than 20 inches of rain fell: 1905, 1941, and 1986. There were 26 years (27% of all years) where more than 15 inches of rain fell and 30 years (31% of all years) where less than 10 inches fell.

The extracted raw data is immediately below. In some of the early years there was a significant amount of missing data. No entry is made where there is no data or a significant amount of missing data. Notes to the side explain the rationale for leaving the raw data in or taking it out.

Annual Rainfall Sorted by Maximum Rainfall to Minimum Rainfall

Post and photograph by Bob Barnes of Hillsboro.