Posted at 2:06 PM on June 1, 2012
by Mark Seeley
This past month brought dramatic, though not unexpected relief to 33 drought-stricken counties in Minnesota. The frequent and abundant May rainfall was the most since 2004 and marked an emphatic end to seven months of severe drought in parts of Minnesota. Some areas received over three times the normal May rainfall amounts.
Based on aggregate averages from cooperative weather station observations May of 2012 shows a statewide mean value for total rainfall of 5.82 inches. Using similar averaging techniques (though numbers of climate stations vary across years), May of 2012 ranks 4th all-time in average total rainfall for the state. The higher ranked years include: 1908 with 5.94 inches; 1962 with 6.06 inches; and 1938 with 6.24 inches.
Besides replenishing soil moisture values, the abundant rainfall helped to restore most Minnesota watersheds to normal or above normal flow volumes. The exceptions seem to be some of the watersheds in the northwest that feed the Red River. They observed somewhat below normal rainfall during the month, For specific flow data on individual watersheds you can use the DNR stream hydrology web site.
Somehow, a statewide precipitation average seems more than a little ingenuous for a state as large as Minnesota and, especially, for a month like May 2012 when some areas received 9 inches on a day when others of us (Rochester for example) received less than a tenth of an inch. I am glad for the additional rainfall for so many, but does this "statewide mean value" really mean (pun intended) anything?