The dry period that began in early summer intensified across Minnesota during September. According to statistics at the St. Cloud Regional Airport, the September 2012 rainfall totalled only 0.24 inches, 3.02 inches below normal. This made September 2012 St. Cloud's second driest September in St. Cloud records. The only drier September was recorded in 1952 when only 0.07 inch fell. 1952 was also the last year in which no September day had at least 0.10 inch of rain.

Largest Partial Growing Season Rain Shortfall Since 1988

The very dry conditions have come since the wet spring mostly ended in May. Between June 1 and September 30, St. Cloud has only picked up 7.41 inches of rain. The average four-month rainfall is 14.73 inches. While three of the past 4 growing seasons have had some kind of dry spell during the growing season, the 7.32 inch deficit in the past 4 months is the largest deficit and the worst than any single growing season since our last major drought in 1986-1989. In fact, June-Sept 2012 has had the third lowest June-Sept rainfall in St. Cloud records. The last year the summer and early fall was drier than this year was in 1950 when only 5.30 inches fell in those four months.

So far in October, the dry conditions have worsened. There has been no measurable rainfall in St. Cloud through October 12, so the St. Cloud rainfall deficit since June 1 totals 8.44 inches. According to the weekly drought report from the Minnesota State Climatology Office, some of the largest rainfall deficits statewide are being seen in a strip of central Minnesota running from Lac qui Parle through Glenwood, Benson, Willmar, Atwater, Paynesville, Annandale, and into Elk River. Rainfall deficits since the start of June are running 7-10 inches since mid-June. Thus, all of central Minnesota is now being listed in the severe drought category by this week's US Drought Monitor. Still, the worst conditions are in northwestern Minnesota, which missed the heavy spring rainfalls, and southwestern Minnesota. These dry conditions could push the ranking of the summer-fall 2012 to near the top of the driest single seasons. In the last 19 days of the month, St. Cloud would have to pick up more than 1.65 inches of rain to avoid beating 1950 as the year with the driest June-October period.

The very dry conditions, combined with a number of windy days, led to several outbreaks of wildfires. The most damaging fire happened in Karlstad in northwestern Minnesota in early October. Many of these fires were put out by an early October snowstorm in northwestern Minnesota, but the generally dry conditions elsewhere were causing problems during any warmer and breezy day.

The heavy spring rains, however, were enough to allow a near normal harvest of corn and soybeans. The toll has been on ground water, which must be replenished before we get too far into next spring's growing season.

Daily Temperature Roller Coaster Much Like a Desert

The "desert-like" conditions led to a roller coaster of temperatures in September, often during the same day. The average September temperature at the St. Cloud Regional Airport was 59.6°F, only 1.0°F warmer than normal. However, that was made up of a 75.5°F average high temperature (5.2°F warmer than average) and a 43.6°F average low temperature (3.2°F colder than average). Nineteen of the 30 September days had at least a 30 degree difference between the high and low temperature with 4 days producing at least a 40 degree temperature difference.

The very dry conditions helped to produce those large ranges by reducing the average greenhouse effect. Water vapor is the most abundant greenhouse gas. During dry weather periods, there is less moisture in the air than average, meaning both that more sunshine gets to heat the ground during the day, leading to warmer higher temperatures, and more earth energy goes directly out to space at night, leading to colder low temperatures. While St. Cloud is not nearly as hot as Death Valley, note that the average range (difference between high and low temperature) during September in Death Valley is about 30-33 degrees, about the same as St. Cloud had averaged in September.

Hottest September High in 34 Years

The actual temperature did break 90 degrees two more times in September, running the 2012 total of 90-degree days to 17 days. That didn't quite make it to the 20 days seen in both 2006 and 2007. That included a record-tying 96 degree high on September 11. That was the latest in the year 90-degree high since 1998 (hit 90 on September 19) and the highest September temperature since 1978 (98 degrees on September 7). A second record was tied on September 29 with a high of 84 degrees.

The relatively cool nights did produce a nearly average date of first frost (September 22, right on the average date) and first hard freeze (September 27, average October 1)

On Pace for Record Warm 2012

Through the first 9 months of 2012, the average St. Cloud temperature has been 52.2°F. That's the warmest average for the first 9 months of the year. The previous high was a whole degree cooler (51.2°F) and was set in 1931. Keep in mind that St. Cloud has already had its warmest year defined by the heating season (July 2011 through June 2012).

    September 2012 Statistics