A monthly electronic newsletter summarizing Minnesota's climate conditions and the resulting impact on water resources.
State Climatology Office - DNR Division of Ecological and Water Resources, St. Paul
distributed: August 7, 2020
What happened in July 2020:
- Precipitation for July 2020 was highly variable. The pattern was typical for summer with clusters of thunderstorms leaving streaks of heavy rainfall, while completely missing other areas. Some counties that had below normal precipitation were Yellow Medicine, Lac Qui Parle and Swift Counties. Sibley and Nicollet County had well above normal precipitation, along with a swath across central Minnesota from Wilkin and Otter Tail Counties, eastward to northern Pine and Carlton County. The highest July 2020 precipitation total from a National Weather Service Cooperative Observer was 8.73 inches near Isle in Mille Lacs County. Some Soil and Water Conservation District rain gage readers in Sibley County had over ten inches for the month, mostly during the mega-rain event of July 25-26. The preliminary state average was 4.40 inches or .38 above normal.
[see: July 2020 Precipitation Total Map | July 2020 Precipitation Departure Map | July 2020 Climate Summary Table ]
There were four notable storm events in July 2020. First, there was a damaging severe storm and tornado event on July 8. The strongest tornado was rated an EF4 that traveled from Grant to Otter tail County to the southeast of Dalton. It was the strongest tornado to strike Minnesota since 2010 and caused one death. This was the first fatality in Minnesota due to a tornado since 2011.
[see: Severe Thunderstorms and Deadly Tornado, July 8, 2020] - The next severe weather event was on July 11. Scattered but intense thunderstorms caused wind and hail damage across southern and central Minnesota. The stronger storms dropped golf-ball to tennis ball-sized hail. Some of the counties impacted were Pope, Kandiyohi, Nicollet, Renville and Jackson Counties. A weak tornado was reported five miles east of Judson in Nicollet County.
[see: Strong Storms Cause Hail Damage to Crops: July 11, 2020] - Two waves of severe thunderstorms pounded parts of Minnesota, first from the evening of Friday July 17th into the following morning, and then again in the evening of Saturday July 18th. Widespread damaging winds were reported in northwestern, northern, and parts of central Minnesota on the 17th. Mercifully, the outbreak was slightly less destructive than had been feared. The storms did produce two short-lived, late-night tornadoes in east-central Minnesota. On July 18th, storms produced large hail and wind damage throughout the Arrowhead, and storms developing near sunset went on to produce tornadoes in Washington County.
[see: Severe Weather and Tornadoes, July 17-18, 2020] - A moisture-heavy air mass unloaded torrential rains for a period of 6-12 hours across a large swath of southern Minnesota from the evening of Saturday July 25th into the morning of Sunday July 26th. The highest known total for the storm came from near Winthrop in Sibley County, where a volunteer observer for the county reported 11.50 inches. Other high totals in that area included 10.70 inches near Lafayette, and 9.15 inches in Gibbon. These amounts are near or exceed the threshold for 500-year threshold for 24-hour rainfall in that part of Minnesota.
[see: Southern Minnesota Mega-Rain, July 25-26, 2020] - The preliminary statewide average temperature for July 2020 was 72.2 degrees or 2.2 degrees above normal. This was the warmest July since 2012. The warmest temperature reported in Minnesota for July 2020 was 96 degrees reported at Browns Valley in Traverse County on July 26 and the coldest temperature of the month was 40 degrees near Brimson in St. Louis County on July 23.
[see: July 2020 Climate Summary Table ]
Where we stand now:
- Seasonal precipitation so far (April 1 through August 4) shows a continuing pattern of the state split by the damp northwest and southeast, to below normal precipitation from west central to northeast Minnesota. Two areas, one along the border of Kittson and Roseau Counties and another area in Sibley County, are ranked in the 99th percentile, or nearly the wettest on record. On the other side of the spectrum, some areas in Lac Qui Parle and Lake Counties are in the 5th percentile.
[see: Seasonal Precipitation Maps] - The U. S. Drought Monitor map released on August 6 depicts 37% of the state in the Abnormally Dry category, and 8% in the Moderate Drought category. One year ago, 94% of the state was free of any drought indicators. 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 levels are much above normal across the Red River Valley, with normal to above normal storm flows across the central and south. Normal to below normal streamflow conditions are over the north central and northeast.
[see: USGS Stream Flow Conditions] - Water levels on Minnesota lakes vary depending on lake and location in the state. Mille Lacs was about two tenths of a foot above average for early August. On August 5, Minnetonka was at 928.81 feet with 12 cfs flowing through Gray's Bay Dam. Minnetonka is about a half foot lower than this time last year. On August 7, White Bear Lake was at 924.85 feet, very close to the same level it was at this time last year. Rainy Lake was within the normal band for lake level. Lake of the Woods was below the median level for early August. Lake Superior was forecasted to be at 603.02 feet on July 31, eleven inches above the July average and two inches below the record August level set in 2019. The lake level in Superior is forecast to stay unchanged over the next month.
[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 August 3 reports that topsoil moisture across Minnesota is 2 percent Very Short, 10 percent Short, 75 percent Adequate, and 13 percent Surplus. Available soil water at Lamberton on July 15 was .47 inches above the historical average. The progress of the corn and soybean crop were about four days ahead of the five year average.
[see: Agricultural Statistics Service Crop Progress and Condition | U. of M. Southwest Research & Outreach Center (Lamberton)] - The potential for wildfires is currently rated by DNR Forestry as Low across southern, west central and east central Minnesota. Moderate potential exists over central and parts of northeast Minnesota, with High potential over the northwest. Historically, 80 percent of all wildfires in Minnesota occur during April and May.
[see: Fire Danger Rating Map]
Future prospects:
- The August precipitation outlook has equal chances for above, normal and below normal precipitation for the state, except in the southwest where there is a slight tilt for above normal precipitation. August precipitation normals range from about two-and-a-half inches in northwest Minnesota to about five inches in southeastern counties. The August temperature outlook leans towards equal chances for below, normal and above normal temperatures across all of Minnesota, with the far southwest corner showing a slight tendency for below normal temperatures. Normal August high temperatures are around 80 degrees to start the month, dropping to the mid-70s by month's end. Normal lows are around 60 degrees early in the month, falling to the mid-50s by late August.
[see: Climate Prediction Center 30-day Outlook | August Temperature Normal Map] - The 90-day precipitation outlook for August through October indicates a tendency for above normal precipitation across the state, especially in the west. The August through October temperature projection also has a tendency fort above normal temperatures not only in Minnesota, but for the entire continental US.
[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:
- What does this winter look like? ENSO-neutral was present though the summer. There is about a 50-50 chance of a transition from ENSO-neutral to La Niña this fall and winter. The current three month outlook from December-February from the Climate Prediction Center has equal chances for below, normal and above normal temperatures and tendency for above normal precipitation, especially in the south. Does this mean a snowy winter? We will see! [see: Climate Prediction Center Dec 20-Feb 21]
Upcoming dates of note:
- August 20: National Weather Service releases 30/90 day temperature and precipitation outlooks
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