Lake Superior, the deepest lake with by far the highest volume of water, is not as warm as the other Great Lakes, but still is running over 6 degrees above average. Boaters and paddlers should monitor marine weather forecasts and be constantly alert to changing conditions.. Average daytime high temperatures range from 60 degrees Fahrenheit in May, to the upper 80s in mid-summer, to the mid-60s in September. Lake Superior is renowned for its cold temperatures, rough seas, fog, and sudden squalls. The average water temperature now is 76 degrees, with the long-term average water temperature at 70 for this date. Lake Superior average water temperature this year (red) versus long-term average. In Superior, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.. Summer surface temperatures in the lake appeared to have increased by about 4.5 °F (2.5 °C) between 1979 and 2007, compared with an approximately 2.7 °F (1.5 °C) increase in the surrounding average air temperature. They operate during the ice-free months each year, and are typically deployed in … The warmest water temperature in Lake Superior in June is 10.3°C/50.5°F, and the coldest water temperature in June is 2.6°C/36.7°F. The western Lake Superior Buoys are maintained by the University of Minnesota Duluth Large Lakes Observatory, with funding from the Great Lakes Observing System. Recent lake temperatures reported that Lake Michigan’s waters have an average temperature of 75 degrees Fahrenheit (24 degrees Celsius) with the temperatures cooler closer to the center of the lake. 1, 2. An average of 7.00°C | 44.60°F water temperatures is reached in Superior (Lake Superior) over the year. Temperature and precipitation statistics for selected towns in the Lake Superior Basin. Whereas in February the lowest value is measured with about 1.10°C | 33.98°F. At 18.20°C | 64.76°F, the average monthly water temperature reaches its highest value in the year in August. Lake Superior's ice cover is diminishing. Average water temperature in Lake Superior in June is 4.5°C/40.1°F and therefore is not suitable for comfortable swimming. Monthly: 1981-2010 normals History: 2007-2019 Temperatures close to the shore have been measured higher than 80 degrees Fahrenheit (27 degrees Celsius and higher). Per decade since 1980, surface water temperature in summer has increased about 2 °F (1 °C), while regional air temperature has increased 1 °F (0.5 °C). Station Data. Lake Superior's surface water temperature in summer has warmed twice as much as the air above it since 1980. Monthly averages Duluth Longitude: -92.1936, Latitude: 46.8421 Average weather Duluth, MN - 55811.