Mid-August Climate Check:

After a cooler than normal first week of the month, temperatures fluctuated above normal this past week evening things out. Most climate stations are now reporting average monthly temperature that is a degree or two either side of normal. Extremes so far have been 92°F at Redwood Falls on the 9th to 36°F at Seagull Lake (Cook County) on the 4th. No immediate shift to extreme temperatures, hot or cold, seems likely the rest of the month.

Rainfall has certainly been mixed this month. Over 50 climate stations have reported 3 inches or more of rainfall this month so far, while over 20 climate stations, mostly in southeastern Minnesota have reported less than an inch of rainfall. Since last Friday widespread thunderstorms have brought significant daily rainfall to many areas, and some climate stations saw daily records set. Some of the new daily record rainfalls over the past week at long term Minnesota climate stations include:

August 8th: 1.80 inches at Cotton (St Louis County); 1.85 inches at Floodwood (St Louis County); 3.97” at Lake Winnibigoshish Dam (Itasca County); and 2.23 inches at Wright (Carlton County)
August 9th: 2.00 inches at Zumbrota (Goodhue County); 1.37 inches at International Falls (Koochiching County)
August 10th: 2.28 inches at Rockford (Wright County); 1.61 inches at Wright (Carlton County)
August 12: 2.95 inches at Redwood Falls (Redwood County)
August 13: 2.06 inches at Long Prairie (Todd County); 2.89 inches at New Ulm 3SE (Nicollet County)
August 14: 2.30 inches at Alexandria (Douglas County)

A number of other locations that do not have long term climate records reported even heavier daily rainfalls, with observers in Edina, Excelsior, Eden Prairie, and Chanhassen reporting over 4 inches on the 10th.

August 8-10 (Sunday-Monday) were two of the busiest days of the summer so far for the NOAA Storm Prediction Center because of widespread severe weather reports (including the derecho storm described below in the “Weather Potpourri”). On Sunday, August 9th there were 48 reports of large hail filed across Minnesota, from 15 different counties. Hail sizes ranged from 1 inch diameter to 2.5 inch diameter. In addition there was a tornado report from near Thief River Falls (Pennington County), as well as damaging wind reports from Roseau, Marshall, Beltrami, Itasca, Hubbard, Hennepin, and Pine Counties with many wind gusts over 60 mph.

Weekly Weather Potpourri:

NOAA reports that a large derecho (straight-line windstorm with a bow echo on radar) formed in northeastern NE, and SW SD early on Monday, August 10th. It moved east over IA, WI, IL, and IN producing rain, hail, and serious wind damage. Wind gusts of 80-100 mph were common along a path that cut a wide swath. You can find more detailed information from the National Weather Service Forecast Office in the QuadCities.

NOAA release its annual State of the Climate Report this week framing 2019 in historical context. The report confirmed that 2019 was among the three warmest years in records dating to the mid-1800s with a short-term warming, but weak, El Niño influence early in the year. It is interesting to note that the coldest geographic anomaly on Earth last year was in the middle of North America.

MPR listener question:

We live in Loretto, MN (western Hennepin County) and saw tennis-size hail in our yard last Sunday (August 9th)? My husband and I wondered what was the largest hailstone that has been reported in Minnesota?

Answer:

Yes, indeed there were many reports of large hail across Minnesota last Sunday, especially in Hennepin and Wright Counties. There have been many cases of tennis ball-size hail (2.5 inch diameter), and even softball-size hail (4 inch diameter) historically in Minnesota. According to official NOAA records the largest diameter hailstones measured in Minnesota were 6 inches, once at Edgerton (Pipestone County) on July 4, 1968; and once in Reading (Township in Nobles County) on July 28, 1986. According to the NOAA National Severe Storms Lab (NSSL) hail of this size mail fall to earth at a velocity of over 70 mph…..quite destructive.

Twin Cities Almanac for August 14th:

The average MSP high temperature for this date is 81 degrees F (plus or minus 7 degrees F standard deviation), while the average low is 62 degrees F (plus or minus 6 degrees F standard deviation).

MSP Local Records for August 14th:

MSP records for this date include: highest daily maximum temperature of 96 degrees F in 1978; lowest daily maximum temperature of 65 degrees F in 1887; lowest daily minimum temperature of 43 degrees F in 1964; highest daily minimum temperature of 72 degrees F in 1978; record precipitation of 1.00 inches in 1981. No snowfall has been reported on this date.

Average dew point for August 14th is 59°F; the maximum dew point on this date is 76°F in 1978; and the minimum dew point on this date is 32°F in 1933.

All-time state records for August 14th:

The state record high temperature for this date is 105 degrees F at Hawley (Clay County) in 1984. The state record low temperature for this date is 25 degrees F at Tower (St Louis County) in 1977. The state record precipitation for this date is 5.29 inches at Gaylord (Sibley County) in 1981. No snowfall has been reported on this date.

Past Weather Features:

It was a frosty morning in northern Minnesota on August 14, 1964. Observers in St Louis, Itasca, Cass, Carlton, and Roseau Counties all reported frosts. The temperature at Cotton, MN started out at 27°F but warmed all the way up to 70°F by afternoon.

August 14, 1965 was the hottest in history for Minnesota with a majority of climate stations reporting afternoon highs in the 90s F. In western Minnesota, Lyon, Nobles, Traverse, Lac Qui Parle, :Polk, Marshall, Wilkin, and Yellow Medicine all reported temperatures of 100°F or greater.

August 14-15, 1981 brought strong thunderstorms to portions of southern Minnesota. Many counties reported 2 to 5 inches of rainfall with some flooded fields and roads.

Outlook:

Relatively cool, sunny, dry, and pleasant weather will settle into Minnesota over the period Saturday through Thursday. Temperatures will track a few degrees cooler than normal. They will be a chance of rainfall towards next weekend.