During a period when American Samoa had been under a Flood Watch, the Weather Service Office at Pago Pago requested that a GOES-18 (GOES-West) Mesoscale Domain Sector be positioned over the region — due to their lack of radar, more frequent satellite imagery can be a critical tool for monitoring the development of deep convection. 1-minute GOES-18 Infrared imagery (above) showed clusters of deep convection that moved across the main island of Tutuila during a 7-hour period on 18-19 May 2026. At the Pago Pago METAR site on Tutuila (NSTU), most of their calendar day 24-hour precipitation for 18 May (5.21 inches) occurred in a 3-hour period during the GOES-18 animation shown above — and several Flash Flood Warnings were issued amid a variety of Local Storm Reports of flooding.

After a small cluster of convection rapidly developed just west of Tutuila shortly before 0000 UTC on 19 May, an overshooting top exhibited an infrared brightness temperature of -80.4ºC at 0018 UTC (below). Convective clusters then produced a thunderstorm with heavy rain showers at Pago Pago during the 0100-0200 UTC time period (METAR observations), contributing to much of the 4.15″ of rainfall that occurred during the 3-hour period ending at 0300 UTC.

In a comparison of 1-minute GOES-18 Visible and Infrared images (below), the overshooting tops of rapidly-developing convective clusters that moved over and near Tutuila were very apparent. The violet pixel in the 0020 UTC infrared image highlighted an overshooting top brightness temperature of -81.0°C.

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1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Visible images (with/without an overlay of the FDCA Fire Mask derived product) and Shortwave Infrared images (above) showed the thermal anomaly associated with a fast-moving grass fire (the Sharpe Fire) that moved northeastward across the Oklahoma border into Baca County in far southeastern Colorado on 17 May 2026 — prompting the issuance of an Evacuation Immediate order for southern Baca County residents in the vicinity of Campo at 2045 UTC. RAWS sites upstream of and near the fire recorded southwesterly wind gusts as high as 45-47 mph.

This grass fire burned very hot, and at 2017 UTC it first exhibited a 3.9 µm shortwave infrared brightness temperature of 137.77ºC (below) — which is the saturation temperature of GOES-19 ABI Band 7 detectors.

1-minute GOES-19 GeoColor RGB images with Next Generation Fire System (NGFS) Fire Detection polygons (below) also showed the rapid northeastward spread of the wind-driven fire’s thermal signature. The surface observation site near Campo, Colorado recorded relative humidity (green) values as low as 4%, and southwesterly wind gusts (red) as high as 45 mph. Note how the wind direction at area observation sites fluctuated from a more northerly-northeasterly direction early in the day to southwesterly later in the day, as a segment of a quasi-stationary frontal boundary briefly surged northward (surface analyses).

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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.

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1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Visible images (with/without an overlay of the FDCA Fire Mask derived product), Shortwave Infrared images and Infrared Window images (above) showed the thermal anomalies associated with several grass fires south and southwest of Dodge City (KDDC) in southwestern Kansas — and two of these grass fires produced pyrocumulonimbus (pyroCb) clouds late in the day on 15 May 2026. The initial (and largest) pyroCb exhibited a 24-minute period of GLM-detected lightning activity (beginning at 2234 UTC, and ending at 2258 UTC).

Each pyroCb initially exhibited cloud-top infrared brightness temperatures in the -40s C (shades of blue to cyan), which is a necessary trait to be classified as a pyrocumulonimbus (since those temperatures assure that heterogeneous glaciation has occurred at the cloud top) — and the coldest cloud-top infrared brightness temperature of the larger pyroCb eventually reached -50.61ºC at 2356 UTC on 15 May (above). According to a plot of rawinsonde data from Dodge City (below), that -50.61ºC temperature represented an altitude not far below the Equilibrium Level (EL) of an ascending Forecast Surface air parcel.

The coldest cloud-top infrared brightness temperature of the second (smaller) pyroCb was -42.31ºC at 0014 UTC on 16 May (below). Note that the cloud material of this second pyroCb had more of a southeastward drift than the first pyroCb — rawinsonde data depicted light northwest winds near the altitude of the -42ºC temperature level (in contrast to westerly winds at slightly higher altitudes near the Equilibrium Level).

1-minute GOES-19 True Color RGB images from the CSPP GeoSphere site (below) better highlighted the dark burn scars of the grass fires, as well as the hazy pall of smoke that was spreading northward and westward (at Dodge City, this smoke reduced the surface visibility to 3-4 miles at times).

The grass fires that produced the 2 pyroCb clouds were burning in Clark County and Meade County — both of which were experiencing Severe to Extreme Drought conditions.

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