September 2011 Saint Cloud Weather Summary

Fourth Driest September

After nearly 8 months in which the rain seemingly never stopped, St. Cloud has suddenly dried out in the past 6 week. The September rainfall at the St. Cloud Municipal Airport totalled only 0.74 inch, 2.72 inch below normal. So, September 2011 ties September 1922 for the fourth driest September in St. Cloud records. More specifically, Saint Cloud has only picked up 1.34 inch of rain between August 21 and September 30. The normal amount of rainfall during that six-week period is 4.91 inches. Lawns and other surface plants have dried out because of the prolonged dry spell.

This comes as a marked contrast to the earlier growing season. Between April 1 and August 20, St. Cloud had 20.81 inches of rain, nearly six inches above the average of 14.90 inches. For the year through the end of September, Saint Cloud is nearly three inches above normal (actual: 26.02 inches; normal 23.04 inches). The long period of dry weather has caused Minnesota topsoil to go from only 2% being short of moisture on August 1 to 54% being short on October 3. Between the start of the year and August 20, Saint Cloud had measurable precipitation on 89 of the first 232 days of the year. That's an average of 2.7 days with rain in the average week. Since August 20, however, St. Cloud has only had measurable rainfall on 7 days out of 41 (now 7 for 44 through October 3). That's only 1.1 days with rain during the average week.

Dry Conditions Enhances Fire Danger

Also, parts of northern and southern Minnesota have ended up 3-6 inches short on rainfall since the end of July and are ranked as having drought on the National Drought Mitigation Center's Drought Monitor. The persistently dry conditions and strong winds behind a cold front led to a lightning-induced fire to spread out of control in the Boundary Waters.

The dryness combined with near record early October warmth has led to extreme fire danger across much of Minnesota this week with a red flag warning in effect for western and southwestern Minnesota.

Why Dry After So Wet?

What produced the turnaround from a soggy spring and early summer to this dry late summer and early fall? A major change in the steering wind pattern finally pushed the persistent humidity out of central Minnesota. At first, this was produced by northwest-to-southeast steering winds that pulled drier air in from Canada. But, as September went on, St. Cloud had its share of warm interludes (September 7-12 had 6 straight 80-degree highs including 4 straight days with a high of 88, the warmest days since August 1). However, that warm air came mostly from the eastern slopes of the Rockies, not from the deep humid air normally over the Gulf of Mexico. There was more cooler Canadian air at mid-month, giving St. Cloud 11 out of 12 days from September 14 through 25 with the highs not making it to 70 degrees. It also included an early season first frost on September 15. For the Saint Cloud Airport, this marked 142 days between frosts (last one in the spring was on April 25), 9 days fewer than normal. However, for much of the northern and central Minnesota, September 15 produced a hard freeze with low temperatures of 28 degrees or colder. That was half a month early (St. Cloud's median hard freeze date is October 1). This early freeze ended up reducing soybean yields. However, the end of the month was marked by the return of warm weather with an 82 degree high on September 28.

Roller Coaster Temperatures End Up Near Normal

Despite all of the ups and downs, Saint Cloud temperatures ended up being very close to normal. The average September 2011 temperature was 58.9°F, 0.3°F warmer than normal.

    September 2011 Statistics