September 2010 Saint Cloud Weather Summary

St. Cloud remained in a stormy weather pattern for most of September, producing the rainiest September in 25 years. The rainfall at the St. Cloud Regional Airport totalled 7.16 inches, nearly two and a half times the normal September rainfall of 2.93 inches. This ranked as the third wettest September in St. Cloud records and the wettest since 1985. The combined August-September rainfall in St. Cloud was 13.52 inches, good enough for 4th place . The highest total is again August and September of 1926 with 17.94 inches.

For the year, St. Cloud has received 27.85 inches of rain, more than the annual average of 27.27 inches. That's also more than the entire years of 2003 and each of 2006-2008.

August Stormy Pattern Continued With St. Cloud On the Cooler Side

The heavy rains were caused by a continuation of the stormy pattern seen in August. Central Minnesota remained along the battleground between relatively cool and dry Canadian air and the intensely hot and humid air that plagued much of the South Central and Southeastern US for the bulk of the summer months. The change to the September pattern from August is that the average front position was pushed further to the south than in August, so St. Cloud had much less severe weather, but more frequently got into the area of heavy rainfall that had frequently set up further south during most of the summer months.

Record Minnesota September Rainfall, But Less to North of St. Cloud

Nearly all of Minnesota had well above normal rainfall during September, producing the highest average statewide rainfall since recent records began in 1891, according to the Minnesota State Climatology Office. The average rainfall of 6.46 inches beat 1900 by just over a quarter inch. The state average was enhanced by a swath of 10-13 inch rainfalls statewide in southern Minnesota just to the south of the Minnesota River. There was a huge change across central Minnesota with over 7 inches in much of Sherburne County, but only 4-5 inches in northeastern Stearns and much of Morrison County. Even these lower totals were more than the monthly average, however. This heavy September rainfall followed a very wet summer in spotty areas across the state . Places like Pine City and Detroit Lakes received over 20 inches of rain during the summer, nearly three-quarters of their annual rainfall.

Would You Believe Still Drought in the Arrowhead?

On the other hand, the least September rain (3-4 inches) fell from the Brainerd Lakes into the Arrowhead. That area, especially Lake and Cook Counties, continue to suffer from a moderate to severe drought, according to the statistics from the National Drought Mitigation Center. The Boundary Waters in the northern parts of these counties have been 4-6 inches short of rain during this growing season. Earlier this summer, the entire Lake Superior Basin was under the most severe drought conditions in the US , thanks to over 2 years of below normal rainfall, but the heavy August and September rains have greatly eased the shortage along the South Shore of Lake Superior .

September 22-23 Produces Flash Flooding and River Flooding

The biggest contributor to the heavy September rainfall totals was the heavy rainstorm on September 22-23 . Nearly 4 inches fell across the southern third of the state with a swath of 8-12 inch rainfalls from the Buffalo Ridge to the south of Mankato. Rainfall reached 11.06 inches near Winnebago (Faribault County) and 10.68 inches in Amboy (Blue Earth County). The St. Cloud Airport missed the first wave of rainfall from these storms, so the storm total was 1.57 inches with 1.52 inch on September 23, just 0.08 inch short of the daily rainfall record .

The heavy rains produced flash flooding in several southern Minnesota towns from Pipestone to Zumbro Falls. Record high levels of water were recorded in several Minnesota streams and rivers, a rare occurrence outside the snowmelt season. Flooding also occurred as the rainwaters moved into the Minnesota and Lower Mississippi Rivers.

Fortunately for the moisture situation, the last week of September and the first week of October have produced a much drier weather pattern, allowing the rivers to fall from their peak after the late September flooding.

Biggest Area Rainfall on September 2

Another serious rainfall on September 2 brought hail up to golf ball sized in Foley and a 62 MPH wind gust in Sartell in the early morning hours. That produced St. Cloud's heaviest rainfall of the month, 1.96 inches of rain, which would have broken a daily rainfall record had it occurred on either the first or the third. It was not the biggest rainstorm of the year, since 2.72 inches had fallen on August 12-13 .

Rainfall Records Tied and Broken

St. Cloud did tie a daily rainfall record with 1.56 inches of rain on September 6 and set a rainfall record with 1.58 inches of rain on September 15. In all, there were 4 days in September with at least an inch of rainfall, which ties 1914 and 1926 as the only Septembers with the most days with at least an inch of rain.

Clouds and Frequent Rain Meant Cool September Highs

The more southern position of the front kept St. Cloud in the cooler air more often, so the average September temperature was 56.8°F, 0.6°F cooler than normal. The coolness was especially felt in the average high temperature of 66.6°F, 4.0°F cooler than normal, and the coolest average high St. Cloud has had since 1993. The constant cloudiness and humidity led to the cool average high. Only 9 of the 30 September days had a high of at least 70 degrees. Duluth also recorded relatively few 70-degree highs in September.

The high humidity kept the first frost out of September at the St. Cloud Airport. The temperature reached 30 degrees on October 3, so the first frost was well past the average date of the first frost (Sept. 22) and fairly close to the latest 10% of frosts (Oct. 6). However, some places in central Minnesota approached freezing on Sept. 22 and broke freezing on Sept. 26. Here are the average first frost dates statewide from the State Climatology Office.

     September 2010 Statistics