The Mind Flayer is implied to have created the storms seen in the Upside Down when he sends a tornado after Will in season 2 with intention to possess the boy.
Will, who I believe has some form of quantum super-positioning whenever he views into/enters the Upside Down in season 2, also appears in a location equivalent to the one he is currently in when he views into/enters the Upside Down.
Every location that Will ends up in has the same storm. It has no visible breaks in the clouds like a normal storm would have, suggesting that it spans a large area and it is unnaturally dense. Storms can easily be classified as Multi-Continental because of systems like hurricanes/typhoons/cyclonic storms, which are known for crossing large areas over the span of a few days to about a month (the record time and distance traveled is held by
Super Typhoon/Major Hurricane John of 1994, which lasted for a total of 31 days and traveled a distance of 13,280 km (8,251.8094 miles), which is much larger than the distance between Panama, Panama and the North Pole, which spans 5,597 miles (9,007.498 km)). Then there is
Typhoon Tip of 1979, which could easily swallow up about half of the United States (from about Dallas, Texas to New York City, New York) due to being at least 2,220 km (1,380 miles) in wind-field diameter.
Is it a completely accurate analogy? Not really since the Mind Flayer's storm is supernatural-in-nature and the hurricanes/typhoons/cyclonic storms that I mentioned are the ones that set the upper level of how big hurricanes/typhoons/cyclonic storms can get, how far hurricanes/typhoons/cyclonic storms can travel, and how long hurricanes/typhoons/cyclonic storms can last on Earth. However, it is the best way that I can support that the Mind Flayer is at least Multi-Continental in Attack Potency at this time.