Patrick Ayd, a meteorologist from the NWS in Duluth, told Boreal Community Media that it has "certainly been a foggy September on the North Shore, and certainly more than normal (at least qualitatively)." While a historical baseline for comparison is limited, Ayd shared, "There is not a great database of a normal frequency of fog occurrence. However, it would be safe to say that it is more than we normally see in September."

This month alone, NWS Duluth has issued 12 Dense Fog Advisories, which is the record for the past 20 years (the next closest year is 2019, with seven issued). In August, six alerts were issued, tying with 2010 and 2018 as the highest number within the past 20 years. 

This month, the Cook County/Grand Marais Airport weather station recorded 59 hours of fog so far, which was the highest for the entire county. For the whole north shore/NE Minnesota area, Duluth "won" with 127 hours of fog. 

Other areas in Cook County, from Schroeder to Grand Portage, recorded between approximately 36 hours (Grand Portage) and 46 hours (Schroeder) of dense fog. 

According to Ayd, "The higher elevations of the North Shore were in the fog longer as the higher terrain was stuck in the low-level clouds. The Grand Marais airport is up the hill, thus its visibility was lower for a longer time."

Two main factors contributed to the prolonged fog event. Ayd shared that the first is a "stagnant weather pattern where we have not exchanged out the low-level airmass near the ground," which allowed a moist airmass to persist. "We just kept a moist airmass hanging around with light winds, a perfect setup for fog," he said. The second is "Lake Superior and its reservoir of cool and damp air," which provided the necessary moisture.

Ayd said that we've finally broken out of that pattern, with "dry westerly winds scouring out the low-level humidity," within the last day or two. 

So, will the fog return? 

Ayd stated that, "fog is something that is very difficult to predict more than a day or two in advance, so it's hard to give any kind of an 'outlook' like we do for temperatures or precipitation," but added, "we are expecting to be under high pressure through early next week, but our dewpoints should be lower, which decreases the probability of fog."