5-minute PACUS Sector GOES-18 (GOES-West) Visible images (above) showed the hazy signature of resuspended volcanic ash (remaining from the 1980 eruptions of Mount St. Helens) that was being lofted from the surface by strong east-southeast winds — which were gusting as high as 38-42 mph at nearby RAWS sites — and being transported west-northwestward on 16 September 2025. Pilot reports indicated that the resuspended ash was reaching altitudes of 10000 ft at 1610 UTC and 7000-8000 ft at 1753 UTC.

In the corresponding GOES-18 Split Cloud Top Phase brightness temperature difference images (below), the resuspended ash exhibited darker shades of blue.

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True Color RGB images (source) from GOES-18 (above) provided good contrast between the hazy resuspended ash and the underlying vegetated landscape — and True Color RGB images from GOES-19 (GOES-East) (below) leveraged a more favorable forward scattering geometry later in the day to reveal that the transport of resuspended ash continued for a longer time period than was apparent in the GOES-18 imagery. The 2 sets of GOES True Color RGB images (both centered at Mount St. Helens) are displayed in the native projection of each satellite.

A side-by-side comparison of True Color RGB images from GOES-18 and GOES-19 — remapped to a common projection using Geo2Grid (below) — similarly showed that the hazy signature of resuspended ash was more apparent later into the day in GOES-19 imagery, due to enhanced forward scattering associated with the GOES-East viewing angle.

In a plot of rawinsonde data from Salem, Oregon KSLE (below) note the transition from east-southeast winds below the 790 hPa (2.1 km) level to southerly winds between that and the 635 hPa (4 km) level — this change in wind direction influenced the transport of resuspended ash, carrying it more northward as the ash reached higher altitudes (which was apparent in the GOES True Color RGB images).

South-facing USGS Johnston Ridge Observatory webcam images (below) offered a ground-level view of the resuspended ash that was being lofted by strong winds on 16 September.

Resuspended ash from Mount St. Helens has also occurred with strong westerly winds.

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1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Visible and Infrared images (above) included time-matched (+/- 3 minutes) plots of SPC Storm Reports — which showed supercell thunderstorms that produced a south-to-north oriented swath of at least 12 tornadoes across central North Dakota on 14 September 2025. With this outbreak, a new record was set for the number of tornadoes in North Dakota during a calendar year.

A plot of rawinsonde data from Bismarck, North Dakota at 1800 UTC on 14 September (below) indicated that the Most Unstable (MU) air parcel’s Equilibrium Level (EL) was at an altitude near 12 km, where the air temperature was around -55C (which closely corresponded to the coldest cloud-top infrared brightness temperatures seen in GOES-19 Infrared imagery).

GOES-19 Visible and Infrared images at 2231 UTC (below) included plots of three SPC tornado reports (T) that were received very near that time — plotted at both their observed surface locations, and at their “parallax-corrected” location (assuming a mean cloud-top height of 12 km). It can be seen that that the parallax-corrected locations were moved NW, closer to the parent supercell thunderstorms.

Another important ingredient helping to produce this tornado outbreak was the presence of climatologically high values of Precipitable Water (below) — the value of 1.39 inch derived from 1800 UTC Bismarck rawinsonde data was above the 90th percentile for 14 September, and not far below the daily maximum value of 1.68 inch.

Hourly SPC Mesoscale Analyses of Precipitable Water (below) depicted the broad corridor of high moisture that was being transported northward across the Dakotas on 14 September.

Some official news from us and our friends @NWSGrandForks:
Following the numerous tornadoes that occurred across central ND yesterday, Sunday the 14th, the record for the total number of tornadoes occurring in the state of North Dakota in a calendar year has been broken. #NDwx pic.twitter.com/u11opgbxmf

— NWS Bismarck (@NWSBismarck) September 15, 2025

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5-minute CONUS Sector GOES-18 (GOES-West) Infrared images (above) revealed the exposed low-level circulation center (LLCC) of Tropical Storm Kiko as the system continued to weaken north of the Hawaiian island of Oahu, and downgraded to a Post-Tropical Cyclone at 1500 UTC on 10 September 2025. Clusters of deep convection developed north of the LLCC after 1400 UTC, which exhibited abundant satellite-detected lightning activity. Note that the LLCC passed just to the east of a semi-stationary yellow ship report around 1301 UTC — that was the RV Kilo Moana (Maritime call sign WDA7827), an oceanographic research vessel.

A comparison of GOES-18 Infrared and Visible images (below) showed that the LLCC was more distinct in the higher spatial resolution Visible imagery — however, the LLCC eventually moved beneath the canopy of growing thunderstorms after 1900 UTC, making it impossible to further track.

The LLCC was also very apparent in GCOM-W1 AMSR2 Microwave imagery (source) not far north-northeast of Oahu at 1150 UTC (below).

ASCAT surface scatterometer winds (source) from Metop-B (at 0735 UTC, when Kiko was still a Tropical Storm) and Metop-C (at 2051 UTC, about 6 hours after Kiko was downgraded to a Post-Tropical Cyclone) are shown below. The depiction of the LLCC wind field was seen to degrade during the ~13 hour period between the two ASCAT images.

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The Great Lakes have a significant amount of thermal mass, meaning it takes a long time for them to cool down as the seasons change from summer to autumn. Often during this time of year, the air overlying the lakes is warmer than the lakes themselves. As water evaporates from the lake surface into the cold, dry air above, it quickly condenses into fog. GOES-19 and the NOAA Buoy Network can work together to identify such an event.

NOAA’s buoys are preimarily intended to measure waves and winds, but many of them have air and water temperatures as well. Here’s a time series of the recent air and water temperature observations from NOAA’s West Superior buoy, located in the middle of western Superior about 30 miles northeast of the Apostle Islands. Here, it is clear that since about 0500 UTC (midnight local time) on 10 September, the water temperature has been at or above the air temperature.

This is a clear recipe for fog as the unsaturated air quickly becomes overwhelmed with moisture that has evaporated from the lake. The buoy itself can confirm this, as it has a system of cameras that show an up close and personal view of conditions at that site.

Of course, there are only a handful of buoys in the otherwise vast expanse of Lake Superior. Most of the lake has no in situ information at all. This is yet another case where satellites can be useful. However, satellite observations of fog can be challenging, especially when relying on the infrared band. This is because fog is such a low cloud that its brightness temperature is effectively the same as the land. Take, for example, this view of the Band 13 (10.7 micron) infrared window channel. Clouds are easy to discern over the upper peninsula of Michigan and eastern Wisconsin, but things are much murkier over western Lake Superior. Is the fog uniform across the lake, or are there clearing spots that cannot be seen from this view because the lake and fog temperatures are basically the same?

This is where RGB views can help add significant insight. In the Day Microphysics view (shown here because local time is from 9-10 AM for these loops) it is evident that there is clearing along the Minnesota shore, where the blue of the surface can be clearly discerned by the greyish color of the fog. Such clearing is impossible to discern from the infrared satellite.

SSEC Researcher Kathy Strabala notes that during the portions of the lunar cycle where the moon is providing a lot of illumination, VIIRS can provide visible-like imagery at night that can also aid in fog detection. For this event, the closest full moon was on 7 September, just two days before. The following image from the VIIRS Direct Broadcast antenna at CIMSS Headquarters illustrates the impact of the moon’s light perfectly. Note that even though it is night, it is easy to see where the fog ends. Thanks, Kathy!

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GOES-19 Day Fog brightness temperature difference (BTD) images with plots of buoy data (above) revealed that Lake Superior buoy water temperatures were generally in the 52-54 F range, with air temperatures within 1-2 degrees F of the water temperatures.

The corresponding Day Fog BTD images with plots of METAR surface reports (below) helped to explain why the aforementioned gap in the fog off the North Shore of Minnesota began to fill in after about 1501 UTC — this was in response to the development of a lake breeze (note the shoreline-parallel cloud line that formed not far inland, along the leading edge of the lake breeze) as daytime heating progressed across the Arrowhead of Minnesota. This lake breeze then acted to draw the fog edge toward the coast.

The GOES-19 Cloud Thickness derived product (below) showed that much of the fog across western Lake Superior was 500-1000 ft thick.

A 30-meter resolution Landsat-8 “Natural Color” RGB image at 1652 UTC (below) displayed the intricate and non-uniform structure of the top of the lake fog layer — and also highlighted the presence of an undular bore east of the Apostle Islands.

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