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Heavy Thunderstorms in Southern Minnesota

Heavy Thunderstorms in Southern Minnesota:

Fast moving heavy thunderstorms crossed portions of central and southern Minnesota over July 19-20 this week. These storms also brought strong winds, with many reports of wind gusts over 60 mph. Fortunately little hail was associated with these storms. The only area to report large hail was Windom (Cottonwood County) where hail stones up to 1.5 inches in diameter were observed.

The heaviest rains occurred in southeastern Minnesota counties and in western Wisconsin, where widespread street flooding, and even mudslides were reported. Many observers reported new daily record rainfalls, including:
5.11 inches at Minnesota City (Winona County)
5.03 inches at Wabasha (Wabasha County)
4.75 inches at La Crescent (Winona County)
4.55 inches at Red Wing Dam (Goodhue County)
4.50 inches at Winona Dam (Winona County)
3.89 inches at Hokah (Houston County)
6.37 inches at Alma Dam (Buffalo County, WI)
6.26 inches at La Crosse (La Crosse County, WI)
4.80 inches at Hillsboro (Vernon County, WI)

More information on these storms can be found at the Minnesota State Climatology office web site. Despite the recent rains, many parts of western Minnesota remain drier than normal for the month, with less than 1 inch of total rainfall so far.

Additional heavy rains were affecting southern Minnesota on Friday, July 21st as well, but total amounts were not yet available for this blog.

Topping 100 Degrees F:

Earlier this week on Monday July 17th the climate observer at Browns Valley (Traverse County) reported an afternoon temperature of 101 degrees F, the highest measured so far this year in Minnesota. Elsewhere Canby, Wheaton and Marshall all hit 98 degrees F that day.

The statistics for the past 40 years (my time as Extension Climatologist) show that 80 percent of the time (32 years), a temperature of 100 degrees F or higher is measured somewhere in the state. More often such readings come from western or southern Minnesota counties. For example, 19 of the 40 years the highest temperature in the state was measured in Traverse, Lyon, Lac Qui Parle, or Redwood Counties. These statistics conform to those of our state climate history all the way back to the second half of the 19th Century. Most of the all-time daily high temperature records for the state come from climate stations in Big Stone, Traverse, Lac Qui Parle, and Yellow Medicine Counties. On rare occasions the state's highest daily temperature for a given year may come from southeastern Minnesota, as was the case in 1985 when Theilman (Wabasha County) reported 103 degrees F on June 10th.

Interestingly enough, both the earliest and latest dates for measuring a temperature of 100 degrees F in state history are held by the same climate station. At Ada (Norman County), along Highway 9 in the Red River Valley, the temperature has reached 100 degrees F as early as April 21 (1980), and as late as September 23 (1936). So, if you like hot weather that is the place to choose. On the other hand, Ada has been as cold as -53 degrees F in the winter (Feb 15, 1936), so have some warm clothes for that season.

Only 1986, 1992, 1993, 1997, 2002, 2010,2014, and 2015 have produced no daily high temperatures of 100 degrees F or greater.

Special Conference at Macalester College this week:

"Transition US National Gathering: Growing a Movement for Resilient Communities" will take place at Macalester College over July 27-August 1. There will be workshops and presentation sessions related to planning and building more resilient communities, lowering carbon emissions, mitigating impacts of climate change, and building on social community strengths. Check out the web link for more information.

Weekly Weather Potpourri:

Earlier this month NOAA scientists announced that the Greenhouse Gas Index based on a global network of measurements of greenhouse gases in the atmosphere over oceans and land, has shown a rise of 40 percent since 1990. This is primarily based on a rise in carbon dioxide, although methane and nitrous oxide are some of the other important gases measured as well.

Also earlier this week NOAA scientists announced that the month of June 2017 on a global basis was the 3rd warmest of record going back to 1880. In addition the global average temperature for the first six months of 2017 was the 2nd highest ever for the same measured period (1880-20170, trailing only that of last year. You can read more at the NOAA News web site.

The United Kingdom Met Office had an interesting discussion online this week about common folklore wisdom related to weather. They dissected the accuracy of this folklore wisdom and found some of it to be valid, and some not so valid. One of the beliefs that proved to be highly invalid was that cows lie down before a rain storm.

A recent paper by Norwegian scientists in the journal Environmental Research Letters describes the disparities in the average carbon footprint among households across the European Union. It is interesting to note that the highest carbon footprints are from the United Kingdom and Greece.

MPR listener question:

It seems that we have had a real rollercoaster ride with temperatures around the state this month. Here in Ely half of the days have brought colder than normal temperatures, and half brought warmer than normal temperatures so far this month. Has Minnesota reported the either coldest or warmest temperature in the nations so far in July?


Indeed temperatures have been highly variable so far this month. We have not reported the nation's highest temperature on any day this month, and we rarely do. For example, earlier this week on July17th when Browns Valley reported a daytime high of 101 degrees F, hundreds of climate stations in western states were warmer than that, topped by 124 degrees F at Death Valley. On the cold side though, Crane Lake, MN did report the coldest temperature in the Nation on July 14th with a morning low of just 37 degrees F. That conforms to our national reputation.

MSP Local Records for July 21st:

MSP records for this date include: highest daily maximum temperature of 105 degrees F in 1934; lowest daily maximum temperature of 69 degrees F in 1927 and 1947; lowest daily minimum temperature of 49 degrees F in 1947; highest daily minimum temperature of 79 degrees F in 1983; record precipitation of 1.36 inches in 1951. No snowfall has occurred on this date.

Average dew point for July 21st is 61°F; the maximum dew point on this date is 78°F in 1983; and the minimum dew point on this date is 40°F in 1947.

All-time state records for July 21st:

The all-time state high temperature for today's date is 113 degrees F at Milan (Chippewa County) in 1934; the all-time state low for today's date is 34 degrees F at Angus (Polk County) in 1947. The all-time state record precipitation for this date is 7.83 inches at Chaska (Carver County) in 1987. No snow has fallen on this date.

Past Weather Features:

By far the warmest July 21st in state history was in 1934. Over 30 Minnesota communities reported an afternoon temperature of 100 degrees F or greater, topped by 113 degrees F at Milan (Chippewa County). The heat was compounded by widespread drought as well. Even the overnight temperature never fell below 80 degrees F at Beardsley, Montevideo, Albert Lea, and Zumbrota making for a very difficult night to sleep.

The coldest July 21st in state history was in 1947 when 15 Minnesota communities reported morning lows in the 30s F. Some mid-summer ground frost was reported from St Louis and Polk Counties in northern Minnesota. The afternoon high temperature at Two Harbors only reached 62 degrees F.

Severe thunderstorms dropped heavy rainfall across southeastern Minnesota on July 21, 1951. Many climate stations reported 3 to 6 inches of rainfall which washed out roads and flooded highways. Caledonia in Houston County reported a record 6.60 inches. Flooding of homes and businesses in the Rochester area was widespread, and the Zumbro River saw one of its highest every flood crests.


Partly cloudy with near normal temperatures for Saturday, and mostly dry conditions. Cooler with below normal temperatures for Sunday through Tuesday, and little chance for rain. Then warming for Wednesday and Thursday to near normal temperatures with a chance for showers and thunderstorms.

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