Wildfire Near Lake Superior’s North Shore
On the afternoon of Friday, 15 May 2026, a wildfire broke out near Two Harbors, Minnesota, along the north shore of Lake Superior. Minnesota State Highway 61 was shut down to traffic and evacuation orders were issued for residents between Two Harbors and Castle Danger. Relative humidity levels were very low, with Two Harbors reporting only 21% RH at the time the fire ignited. While winds were low at the time the fire began, since then speeds have picked up and gusts in excess of 20 mph have been reported. This makes it challenging to keep the fire contained and as of the morning of the 16th this fire, dubbed the Stewart Trail fire, has spread to encompass 375 acres.
Taking a look at the satellite perspective, let’s start with the true color loop from GOES-19 (GOES West). If you didn’t quite know what to look for, it might be a challenge to identify where a fire is in this loop.In the middle of the image, in the second half of the loop, you might see a small smoke plume originating right next to the shore and streaming off to the east-northeast. However, the cumulus clouds are somewhat obscuring this plume and overall it’s a challenge to see where a fire might be when it’s young like this.
Fortunately, we have other bands available to us. GOES Band 7 (3.9 microns) is an excellent tool for detecting and monitoring fires, and this case is no exception. The 3.9 micron band is very sensitive to objects with fire-like temperatures, so it is able to note the presence of fire when longer-wavelength bands don’t show a signal. You can watch this loop from 1900-2100 UTC (2:00 PM to 4:00 PM CDT) and easily identify the location of the fire as the large dark spot next to Lake Superior that appears midway through. Note that during the day this time of year, Superior appears cooler than the surrounding land thanks to its massive thermal inertia.
The Fire RGB product also helps us detect fires by combining fire signals from three different shortwave channels. As a fire grows more intense, its signal will appear on shorter wavelength channels. Here we see the fire clearly show up as a set of red pixels. This means that the fire is on the lower end of intensity, even though it is still a significant fire.
Of course, while geostationary satellites excel in temporal resolution, their spatial resolution is not as good as that of the polar orbiting systems. Taking a look at the true color image from NOAA-21 at 1951 UTC (2:51 PM local), it’s a little easier to pick up the smoke plume than it was with the geostationary satellite.
But what happens when we look at a band sensitive to fire temperatures? VIIRS offers the I4 Band, with 375 m resolution at 3.74 microns. There is a noticeable black spot in the center of the image corresponding to the location of the fire. Note how this is much smaller than the black spot seen on the geostationary. This VIIRS view is more likely to be an accurate assessment of the true size of the fire at the image time, which means it can be a valuable tool for forecasters, emergency managers, and first responders.
In fact, we can compare the GOES and VIIRS directly. Use the slider to se how the apparent extent of the fire changes depending on the resolution of the instrument used to monitor it. This time, 1951 UTC, is early in the fire’s development and so it barely appears as a signal in GOES. However, it is readily apparent as a small but intense patch in VIIRS.