GOES-18 imagery from the CSPP Geosphere site, above, shows a thin line of trade wind cumulus from which strong convection develops over Tutuila (the main island of American Samoa). The heavy rains prompted the issuance of Flood Advisories. What products or imagery might have helped in anticipating this convective development?

LightningCast probabilities between 0000 and 0100 UTC on 8 June, below, computed using this CSPP Geo software, show small probabilities developing by 0100 UTC. A forecaster viewing these fields might see them and conclude that something bigger is about to commence.

The Clean Window infrared imagery below, from 0040 – 0110 UTC on 8 June 2025, shows the development of the convection at the western tip of Tutuila. Cooler brightness temperatures are apparent at 0050 UTC — that an the increase in LightningCast probability (shown above) might be enough to convince a forecaster that convection is starting.

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GOES-18 Lifted Index fields, a field that is computed in clear skies only, shows an atmosphere slowly destabilizing around Tutuila from 2300 on the 7th to 0210 on the 8th, changing from about -1.1 to -1.7. So — the cumulus line is approaching an area that is becoming less stable. Strong convection has developed by 0200 UTC.

It’s worth mentioning that parallax errors from GOES-18, overhead at 137.2^oW (compared to 171^oW for Pago Pago) means that the convection that is mapped to the west of Tutuila is, in reality, over the island. Parallax computations (link) suggest that a 30000-foot storm top would be displaced by almost 9 km, or about 4 pixels. The convection was also developing in a region with a bit more moisture (as diagnosed by GOES-R Total Precipitable Water, TPW, below). Regions just east of Tutuila become more moist over the course of the animation below; TPW increases from about 1.8″ to 2″

The Pago Pago sounding from 0000 UTC on 8 June 2025, below, shows abundant instability available if a modest capping inversion can be broken.

Thanks to WSO Pago Pago for alerting me to this challenging case. The interpretation of the Lifted Index is very much simpler because the colorbar bounds were changed! Change defaults to highlight subtle features.

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Given that the narrow lines of tradewind cumulus are possible regions of convective development, what tools are available to monitor them at night? The Day Night Band on NOAA-20/NOAA-21/Suomi-NPP produces visible imagery at night. The image below, from the NASA Worldview site, shows a narrow line of tradewind cumulus approaching the Samoan Islands and the convection from earlier moving north of the islands. June 8th was two days before a full Moon, so there was ample illumination.

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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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