Today at 17:40 UTC, NOAA decommissioned one of its three remaining legacy polar-orbiting weather satellites, NOAA-18. The spacecraft was launched on May 20th, 2005, and was declared operational on August 30th, 2005. For nearly 20 years, NOAA-18 collected weather information across the whole globe, with every point on Earth in view, at minimum, every 12 hours.

The final NOAA-18 orbit collecting data over the continental United States occurred around 16:08 UTC today. At this point, the AVHRR visible/IR imaging sensor was no longer collecting infrared bands 4 and 5. The HRPT direct broadcast signal during this overpass was collected by SSEC’s X/L-band tracking antenna in Madison, and processed using EUMETSAT’s AAPP and CSPP Polar2Grid software:

Band 1: “Red Visible” [0.63 µm]	Band 2: “Vegetation Near-IR” [0.86 µm]	Band 3A: “Snow/Ice Near-IR” [1.61 µm]

Of NOAA’s 5th generation POES spacecraft, 2 remain active: NOAA-15 and NOAA-19. Both are expected to be decommissioned later this summer. Prior to today, the last NOAA polar weather satellite to be decommissioned was NOAA-16 on June 9th, 2014. The JPSS constellation (S-NPP, NOAA-20, and NOAA-21) remains active as NOAA’s primary polar-orbiting weather satellites.

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True-Color imagery and GOES-R Aerosol Optical Depth (AOD) imagery from early on 5 June 2025 (the imagery was captured from the CSPP Geosphere site) from GOES-West, above, and GOES-East, below, shows the a smoke plume emanating from fires in western Canada and spreading over all of southern Canada. The smoke has occasionally pushed south into the United States, as noted in recent CIMSS Blog Posts (and elsewhere). The smoke plume can be thick enough that it is misclassified as cloud in the AOD algorithm. The misclassification is affected by both satellite view angle and solar zenith angle.

What do NGFS detections look like for this ongoing event? NGFS can detect fires using observations from GOES-R or JPSS Satellites; the imagery below from the NGFS RealEarth site shows NGFS microphysics RGB imagery computed using NOAA-21 data. NOAA-21 data are downloaded at direct broadcast antennas with fire detections and imagery created in a very timely manner. Many detections are shown for this widespread wildfire event.

The zoomed-in view below highlights the much greater horizontal resolution of NOAA-21 v. GOES-18 over northern Canada. The higher resolution is the great advantage of JPSS satellites at high latitudes in describing the horizontal extent of a fire . The NGFS microphysics RGB imagery shows well-defined hot regions as purple that are also identified as detections. GOES-18 struggles to see many of the fires at such a high latitude.

The toggle below compares the NOAA-21 and GOES-18 NGFS detections only (that is, it doesn’t include the NGFS microphysics RGB only image that is included in the toggle above).

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The GOES-19 view of the Northern Hemisphere on the morning of 3 June 2025 showed enhanced aerosol optical depth (AOD) across much of its domain. Large regions of elevated AOD are ceen in the eastern half of the continental United States extending out into the western Atlantic Ocean, while the eastern Atlantic, especially off the coast of north Africa, also shows very high AOD levels. However, the causes of these regions of high aerosol content are very different, and satellites can be used to discern just how these regions differ.

First, a word about AOD observations from satellite. The AOD is calculated using multiple wavelengths between 0.4 and 2.25 microns. In essence, the clear-sky reflectance that a satellite expects to see based on time of day, sun angle, and the like is calculated for several different AODs. Changing the amount of aerosols in the sky impacts the amount of reflectance, and the satellite observations of reflectance are compared to the simulated counterparts. The simulation with the best match represents the observed AOD. Since this product depends on visible and near-infrared wavelengths, it is only available during daylight hours. Furthermore, solar glint can dramatically impact the assumed and calculated reflectance values; as a result, a circle of excluded values is clearly present in the above image. You can easily monitor AOD values from the CSPP Geosphere site.

As frequent readers of the Blog know, wildfires in south-central Canada are having a significant impact on the air quality in the eastern continental United States. However, the local impacts of the smoke have been highly variable. NOAA’s High Resolution Rapid Refresh (HRRR) model can be run in a smoke mode that identifies locations and predicts the trajectories of smoke in three dimensions. For example, the GOES-19 true color view over the lower peninsula of Michigan and southern Ontario clearly shows the strong presence of smoke.

The vertically integrated smoke product from HRRR quantifies the total column smoke content. The model clearly captures the extent of the smoke, with some of the highest concentrations found in this Michigan/Ontario region.

However, surface visibilities aren’t that strongly impacted in this region. The ASOS observation for Detroit Wayne County International Airport at 1500 UTC (11:00 AM) indicated that visibility was 9 miles. Since the visibility sensors only observe a maximum of 10 miles, this meant that the visibility was only slightly affected relative to normal. It turns out that the people of this area were relatively lucky: a lack of mixing meant that the smoke remained lofted and that local air quality was largely unaffected. The HRRR smoke forecast of surface level reflects this.

By contrast, Duluth, Minnesota, on the western tip of Lake Superior, is located at the heart of the band of elevated near-surface smoke. Its ASOS observation at the same time confirms this, with visibility only 3 miles.

As noted above, the the continental US and western Atlantic aren’t the only places where GOES-19 is viewing high aerosol loads. The eastern Atlantic adjacent to Africa is also registering high values. However, instead of smoke, this is caused by Saharan Dust being blown out to sea. Given that this is on the extreme edge of the GOES-19 field of view, the pixels can appear somewhat distorted when remapped.

However, when viewed by the Flexible Combined Imager (FCI) instrument aboard EUMETSAT’s now-operational Meteosat-12 satellite, the structure of the dust becomes much more clear. With a deployment over 0 degrees of longitude, Meteosat-12 is well-situated to capture events in Africa, and this dust protrusion is no exception.

We can examine the differences in the Dust RGB (quick guide here) between North America and Africa to see if there’s any insight we can glean from the radiative perspective. The North American image (top panel) does not seem to show much signal at all. The Great Lakes appear to be salmon colored, largely a function of cloud free skies and relatively cool lake surface temperatures. By contrast, the dust over Mauritania appears as a bright fuchsia color, since dust exhibits large 12.3–10.3 differences and the underlying surface is warm.

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10-minute Full Disk scan GOES-18 (GOES-West) “Clean” Infrared Window (10.3 µm) images and “Red” Visible (0.64 µm) images with an overlay of the FDCA Fire Mask derived product (above) showed that a large wildfire south of La Ronge (station identifier CYVC) in central Saskatchewan produced a pyrocumulonimbus (pyroCb) cloud during the afternoon hours on 02 June 2025. The pyroCb-producing fire was located along the western edge of a cluster of wildfires straddling the Saskatchewan/Manitoba border.

The pyroCb initially exhibited cloud-top 10.3 µm infrared brightness temperatures (IRBTs) in the -40s C (denoted by shades of blue to cyan) — a necessary condition to be classified as a pyroCb — beginning at 2020 UTC (below); nearly 7 hours later, the coldest pyroCb cloud-top IRBT had cooled to -51.53ºC at 0300 UTC on 03 June. The peak wind gust at La Ronge during the time period shown was 43 knots (49 mph). Note that in western Manitoba haze (not smoke) restricted the surface visibility to 3/4 mile at The Pas (CYQD) and 1-1/4 mile at Norway House (CYNE) by 0300 UTC on 03 June — this was due to blowing dust originating in Saskatchewan (more on this blowing dust later in the blog post).

A plot of rawinsonde data from The Pas, Manitoba (CYQD) at 0000 UTC on 03 June (below) included a cursor sample of the height at which the coldest GOES-18 cloud-top infrared brightness temperature of the pyroCb occurred (sensed over Saskatchewan at 0300 UTC). This air parcel height was around 0.5 km above that of the CYQD tropopause.

A toggle between the GOES-18 Infrared image at 2130 UTC — with/without an overlay of GLM Flash Extent Density (large dark-blue pixels) (below) showed there was a brief period of satellite-detected lightning activity associated with this pyroCb as it was located southeast of La Ronge CYVC (there was also lightning seen with some of the convection southwest of La Ronge).

The cluster of wildfires straddling the Saskatchewan/Manitoba border was also depicted by Next Generation Fire System (NGFS) fire detection polygons (below), along with the formation and growth of the pyroCb cloud (brighter green enhancement).

In a 14-hour animation of GOES-18 daytime True Color RGB images and Nighttime Microphysics RGB images from the CSPP GeoSphere site (below), after sunset the large plume of blowing dust (brighter shades of magenta) was evident as it was transported eastward across Manitoba and Ontario, just ahead of the cold (darker-red-with-intermittent-yellow-pixels) Saskatchewan pyroCb. This blowing dust was lofted by strong winds blowing across recently-plowed agricultural fields (located in central Saskatchewan, south of the wildfires burning in more northern boreal forest areas of the province).

In an animation of GOES-19 (GOES-East) Nighttime Microphysics RGB and daytime True Color RGB images (below), after sunrise on 03 June the tan-colored mixture of blowing dust and wildfire smoke was seen wrapping northward across eastern Hudson Bay (around the eastern periphery of a large area of low pressure that was centered over the Nunavut/Manitoba border at 12 UTC on 03 June).

A toggle between Suomi-NPP and NOAA-20 VIIRS True Color RGB images — visualized using RealEarth (below) also showed the plume of dust/smoke wrapping cyclonically across Ontario and Hudson Bay on 03 June.

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