A monthly electronic newsletter summarizing Minnesota's climate conditions and the resulting impact on water resources. Distributed on the first Thursday of the month.
State Climatology Office - DNR Division of Ecological and Water Resources, St. Paul
distributed: October 9, 2020
What happened in September 2020:
- September 2020 finished well below normal for precipitation statewide. The preliminary average for Minnesota was 1.84 inches or 1.47 inches below normal. The dry September was nearly universal in the state, with only a few locations in southeast Minnesota finishing above normal. One of the wettest locations was at Caledonia in Houston County that wound up with 5.42 inches or 1.62 inches above normal. One of the driest locations was the Duluth International Airport, where only 0.85 inches fell during the month, making it the 7th driest September on record for that station. Since January 1, there has been only 15.04 inches of precipitation at Duluth, the third driest on record. Only 1918 and 1934 were drier.
[see: September 2020 Precipitation Total Map | September 2020 Precipitation Departure Map | September 2020 Climate Summary Table | September 2020 Percent of Normal Precipitation Map]
- September 2020 had one severe storm episode of note for the month:
- Hail the size of tennis-balls fell with storms near Olivia on September 5. There were many reports of quarter to golf-ball size hail in south central Minnesota, including the western and the southern Twin Cities.
[see: Severe Storm Reports for September 5, 2020 from the Storm Prediction Center]
- September finished cooler than normal statewide, with a preliminary average statewide temperature finishing 1.2 degrees below normal. That said, the entire month was not consistently cool either. The cold episode from September 8-11 set some record cold high temperatures, including a record cold high temperature of 50 degrees in the Twin Cities on September 9. Summer had a bit of a rebound from the 21st to the 25th with many high temperature readings in the mid 70’s to the mid 80’s in the state.
Places in the central and north had a light frost in mid-September, with southern Minnesota having a light frost by the first week of October. St. Cloud had its first 32 or colder on September 10, Waseca and Rochester on October 2 and the Twin Cites hit 32 degrees on October 4. First frost was a little early for central Minnesota but close to the median in the south. The warmest temperature found for September was 89 degrees on September 15 at Marshall in Lyon County and the coldest temperature found for the month was 20 degrees on September 18 at Baudette, International Falls, Embarrass and Babbitt in northwest Minnesota.
[see: September 2020 Climate Summary Table | 2020 September Departure from Normal Temperature Map]
Where we stand now:
- Seasonal precipitation totals (April 1 through October 6) ranked above the historical median over northwest and parts of west central and south central Minnesota. Two small areas in Kittson and Roseau Counties and another area in Sibley and Nicollet Counties are in the 99th percentile for the wettest growing season. Southwest and northeast Minnesota are in the 20th percentile or less below normal ranking.
[see: Seasonal Precipitation Ranking Maps]
- The U. S. Drought Monitor map released on October 6, depicts areas of drought that have expanded since last month. A very small area in southwest Minnesota is in the Severe Drought category. Twelve percent of the state is in the Moderate Drought category, especially in northeast and southwest Minnesota. Just under half the state is in Abnormally Dry conditions. Last year at this time the entire state was free of any drought designation. The U.S. Drought Monitor index is a blend of science and subjectivity where drought categories (Moderate, Severe, etc.) are based on several indicators.
[see: Drought Conditions Overview]
- The U.S. Geological Survey reports that stream discharge values are generally normal to below normal across the state. There are still some above normal stream flows in Houston County and in the Red River Valley. There are below to much below normal stream flows over northeast Minnesota, with even some low flow conditions reported.
[see: USGS Stream Flow Conditions | Weekly Stream Flow Maps and Tables]
- Water levels on most Minnesota experienced a decline across the state due to the dry September. Mille Lacs was just above the median lake level for September. On October 7, Minnetonka was at 928.58 feet and the Grays Bay Dam closed on October 5. White Bear Lake was at 924.26 feet on October 4, a fall of .8 (eight tenths of a foot) from one year ago and by the end of September the water flowing out of White Bear Lake was down to a trickle. Rainy Lake was on the lower end of the median band and Lake of the Woods was well below in the median range for early October. Lake of the Woods was in the 5th percentile. Lake Superior was at 602.95 feet on October 2, ten inches higher than the average October level, but four inches lower than the water level from October 2, 2019.
[see:Mille Lacs Lake Water Level | Lake Minnetonka Water Level | White Bear Lake Water Level | Lake of the Woods Control Board Basin Data | Corps of Engineers Great Lakes Water Levels]
- The Agricultural Statistics Service on October 5 reports that topsoil moisture across Minnesota is 2 percent Very Short, 12 percent Short, 80 percent Adequate, and 6 percent Surplus. Maturity of corn was two weeks ahead of the five year average and three weeks ahead of last year. Soybeans were five days ahead of average. The dry streach of weather has been very beneficial for harvest this year. Soil moisture levels at Lamberton and Waseca are well above the historical median. The soil moisture level at Lamberton is 7 seven tenths of an inch above the historic average.
[see: Agricultural Statistics Service Crop Progress and Condition | U. of M. Southwest Research and Outreach Center (Lamberton) | U. of M. Southern Research and Outreach Center (Waseca)]
- The potential for wildfires as of October 14 rated by DNR Forestry as Extreme across southwest and south central Minnesota, High across southeast Minnesota, Moderate across west central and east central Minnesota and Low across northwest, northeast Minnesota and part of central Minnesota. Historically, 80 percent of all wildfires in Minnesota occur during April and May.
[see: Fire Danger Rating Map]
- It looks like the dry and warm pattern at the beginning of October is forecast to continue though the month. The October precipitation outlook leans towards well below normal precipitation across the entire state, especially in the southwest. October precipitation normals range from about one-and-a-half inches in northwest Minnesota to about three-and-a-half inches in Cook County. Southern and central Minnesota range by about one-and-three-quarters of an inch in the southwest to about two-and-a-half inches in east central Minnesota.
[see: Climate Prediction Center 30-day Outlook | October Precipitation Normal Map]
- The October temperature outlook has a strong tendency for above normal temperatures throughout Minnesota for October, with the best chance in the northwest. Normal October high temperatures are in the 60's to start the month, dropping to the low 50's to upper 40's by month's end. Normal lows are in the 40's early in the month, falling to the 30's by late October.
[see: Climate Prediction Center 30-day Outlook | October Temperature Normal Map]
- The 90-day temperature outlook for October through December has a tendency of above normal temperatures. The 90-day precipitation outlook for October through December indicates equal chances of below-normal, near-normal, or above-normal conditions across most of Minnesota.
[see: Climate Prediction Center 90-day Outlook]
- The National Weather Service produces long-range probabilistic river stage and discharge outlooks for the Red River, Minnesota River, and Mississippi River basins. These products address both high flow and low flow probabilities.
[see: National Weather Service - North Central River Forecast Center]
From the author:
- Smoke and haze from western US wildfires drifted over Minnesota in the middle of September. The high-altitude smoke dimmed the sunshine, reduced the solar radiation and causing some spectacular sunsets as well.
[see: Smoky Skies: September 13-15, 2020]
Upcoming dates of note:
- October 15: National Weather Service releases 30/90 day temperature and precipitation outlooks
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Pete Boulay, DNR Climatologist