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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With numerous wildfires burning across the boreal forest regions of Alberta/Saskatchewan/Manitoba during late May 2025, dense smoke began to move southward across much of the north-central US beginning on 30 May. GOES-19 (GOES-East) True Color RGB images along with the Aerosol Optical Depth (AOD) derived product from the CSPP GeoSphere site (above) showed the areal coverage and transport of this wildfire smoke on 30 May.

For the most part, the majority of this smoke remained aloft — and only reduced the surface visibility (the number at the bottom of each Ceiling/Visibility plot, in statute miles) at a handful of sites across northern Minnesota, northern Wisconsin and eastern Iowa (below).

A Pilot Report over far northern Minnesota (below) indicated that smoke was reducing the visibility to 5 miles at an altitude of 5500 feet.

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On 31 May, GOES-19 True Color RGB and AOD imagery (below) revealed that some of the smoke was becoming entrained into the circulation of a compact area of mid-tropospheric low pressure that was moving southward from the Dakotas to Nebraska.

Smoke became particularly dense just north of this low, as it descended into the boundary layer — and the surface visibility was reduced to 1-2 miles at several sites across North and South Dakota (below).

The depth of the smoke layer was notable — while the surface visibility was 2-1/2 miles at Watertown SD (KATY), a Pilot Report over that location indicated that haze was reducing the visibility to 5 miles at an altitude of 12,000 feet (below).

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Dense wildfire smoke persisted across much of the region on 01 June, as shown by GOES-19 True Color RGB and AOD imagery (below).

The surface visibility restrictions were generally confined to the eastern Dakotas/Nebraska and western Minnesota/Iowa (below).

While the surface visibility was 5 miles at Sioux Falls SD (KFSD), a nearby Pilot Report noted that haze was restricting the visibility to 3 miles at an altitude of 2200 feet (below).

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Daily CSPP Geosphere imagery (direct link) showing 1710 UTC imagery from 25-29 May 2025, above, depict the slow organization and intensification of an area of disturbed weather south of Mexico (discussed here) as it became Tropical Storm Alvin, the first storm of the eastern Pacific Hurricane Season. This is the 4th Alvin storm in the tropical east Pacific, following ones in 2019 (that was named on June 26th, strengthened to a hurricane, and was present for almost 4 days), 2013 (that was named on May 15th and remained a tropical storm during its short life) and 2007 (that was named on May 28th and remained a tropical storm). The 2025 version of Alvin is not forecast to make landfall; it is forecast to move north and dissipate over the weekend.

Scatterometry data captured from this KNMI website, below, shows two overpasses early on 29 May 2025, one from HY-2B and one from Metop-B. A closed circulation center and tropical storm-force winds are apparent.

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Upper-level water vapor imagery, below, shows the cold convective cloud tops associated with the developing system. Alvin is embedded within a moist airmass. The favorable environment suggests slow strengthening as indicated in the forecast.

The National Hurricane Center is issuing advisories on Alvin every 6 hours here.

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