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August climate trends

August climate trends:

Since the record-setting cold August of 2004, the month of August has been warmer than normal 75 percent of the time (9 years out of 12) in Minnesota. Over the same time period the August rainfall has been quite mixed, with 3 years near normal, 4 years drier than normal, and 5 years wetter than normal. Last year, 2016 brought the 7th wettest month of August in state history, with average rainfall across the state totaling close to 5.5 inches.

So far the pattern for this August (2017) has favored cooler than normal temperatures with highly variable rainfall. Brimson, Embarrass, Hibbing and Crane Lake have already reported morning lows in the 30s F. Thunderstorms over August 3-4 brought 1 to 2 inch rains to some parts of the state, and even set new daily records for some climate stations. Canby reported a record 1.87 inches of rain on the 3rd, while Rochester and Minnesota City reported record rainfalls on the 4th with 2.01 inches and 2.13 inches respectively. August 9th also brought thunderstorm rainfall to portions of Minnesota with some observers reporting well over 1 inch. Cass Lake (Cass County) reported a record 1.66 inches, while Wadena reported a record 1.41 inches.

For the balance of the month it appears cooler than normal temperatures may persist, and a wetter than normal pattern for the remainder of the month is also projected.

Climate Change and Isle Royale National Park:

I recently visited Isle Royale National Park with my wife. We learned a great deal about the natural resources and wildlife there, even saw some moose. Isle Royale has been in the National Park system since 1940, and there are three automated weather stations deployed across the island, plus the cooperative climate station on Mott Island run by the National Park Service since November of 1940. Data are generally available for the May-September period as the park is not staffed from October through April, except for those conducting biological research. Though climate measurements there are not comprehensive enough to do a trend analysis, most of the warmest summers at Isle Royal have occurred since 1983, with the record warmest in 1998. Because Lake Superior slowly warms all summer, releasing higher quantities of water vapor with each passing month, the wettest months there are traditionally in August and September, when monthly rainfall has exceeded 8 inches.

There are some climate change impacts going on there which have caught the attention of the National Park Service. Some of these include:
-Generally warmer winters have caused less frequent ice bridges which provide a means for wildlife to travel from the island to the mainland (usually Ontario, Canada or Minnesota). This is associated with a decline in the wolf population which now stands at only two.
-With rising temperatures some of the inland lakes on Isle Royale have been warming to the point where cold water fish like the Cisco can no longer survive in them. Water temperatures above 67 degrees F are not suitable for Cisco.
-Some Arctic plant species, like the pale paintbrush, may slowly disappear from the island as a result of warming temperatures.
-Warmer springs are linked to more abundant winter ticks, which live on moose and produce added stress. Moose already suffer from some stress due to warmer summer temperatures, and therefore spend more time in the cool waters of the island.

Obviously as the climate continues to change around Lake Superior, Isle Royale will see even more impacts in the future. More information on climate change as it relates to Isle Royale National Park can be found in a report by the Great Lakes Integrated Sciences and Assessment Program.

Weekly Weather Potpourri:

On Thursday, August 10, NOAA released the 2016State of the Climate Report. It is well worth the read, or at least reading the highlights of the report. Some of the main points included:
-A record warm year globally in 2016, third consecutive year of record warmth
-A record rise in sea level in 2016, and a record high in global sea surface temperature, strong El Nino
-Continued rapid loss of Arctic sea ice, as the Arctic warms at twice the rate of the lower latitudes
-Mass of the Greenland ice sheet reaches a record low in 2016
-a record low spring snow cover was measured over the North American Arctic in 2016

In somewhat related news the Finnish Ice Breaker MSV Nordica set a new record for the shortest transit time through the Arctic Northwest Passage, cutting a path from Alaska to Greenland over a period of just 24 days this summer. You can read more at NOAA News Features.

A recent study from the University of Illinois documents how climate change, through late winter or early spring warming, can cause different grass plants to prematurely break dormancy and start growing rigorously, only to be confused by the shorter days that still persist. They then grow shorter shoots, or stop growing entirely, waiting for day length to get long enough to resume grow.

A study recently published in the journal Science documents that climate change, most notably winter warming, is causing more frequent late winter and early spring flooding across many European watersheds. This is the first comprehensive study that reveals this effect of climate change.

MPR listener question:

Here near Roseau, MN we have recorded no measurable rainfall so far this month. Has there ever been an August with no rainfall?


At Roseau the driest August in history was in 1894 when just 0.48 inches of rain fell. There are a few Minnesota climate stations that have recorded a completely dry month of August, including Crookston (Polk County) which received only a trace of rain in August of 1915, and more recently Warren (Marhsall County) which saw no rainfall in August of 2000.

Twin Cities Almanac for August 11th:

The average MSP high temperature for this date is 80 degrees F (plus or minus 7 degrees F standard deviation), while the average low is 61 degrees F (plus or minus 6 degrees F standard deviation).

MSP Local Records for August 11th:

MSP records for this date include: highest daily maximum temperature of 97 degrees F in 1947; lowest daily maximum temperature of 65 degrees F in 1964 and 2004; lowest daily minimum temperature of 47 degrees F in 1968 and 2004; highest daily minimum temperature of 77 degrees F in 1947; record precipitation of 1.73 inches in 2007. No snowfall has occurred on this date.

Average dew point for August 11th is 57F; the maximum dew point on this date is 74F in 2007; and the minimum dew point on this date is 32F in 1999.

All-time state records for August 11th:

The all-time state high temperature for today's date is 105 degrees F at Wheaton (Traverse County) in 1947; the all-time state low for today's date is 28 degrees F at Embarrass (St Louis County) in 199t7. The all-time state record precipitation for this date is 8.06 inches at Hastings (Dakota County) in 1945. No snow has fallen on this date.

Past Weather Features:

Strong thunderstorms crossed the state over August 10-11, 1909 bringing 3 to 5 inches of rain to many areas, especially northern counties. Detroit Lakes reported well over 5 inches, and many farm fields in Becker County were flooded.

A severe thunderstorm passed over Dakota and Goodhue Counties late on August 11 and over the early morning hours of August 12, 1945 bringing 6 to 8 inches of rainfall. Many roads and highways were flooded, along with several farm fields. The Zumbro River rose five feet above flood stage.

The hottest August 11th in state history was in 1947 when 10 Minnesota communities reported afternoon temperatures of 100 degrees F or higher. It was also a difficult night for sleeping as the temperature never dropped below 80 degrees F in some southwestern counties.

The coldest August 11th in state history was in 1997 when overnight temperatures fell into the 30s F across northern Minnesota. Frosts were reported in St Louis and Koochiching Counties.


Mostly sunny and cooler than normal temperatures across the state over the weekend. There will be a chance for scattered showers and thunderstorms later on Sunday, especially in southern counties. Cooler than normal temperatures will continue early next week as well. Temperatures will warm to near normal values by Wednesday with a chance for showers and thunderstorms.
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Thanks for continuing to post to this blog, Mark. Really great information.