A 29-day sequence of 10-minute Full Disk scan GOES-18 (GOES-West) daytime True Color RGB and Nighttime Microphysics RGB images — created using Geo2Grid (above) — showed the evolution of a long-duration Tule fog event across the Central Valley of California, from 21 November to 19 December 2025.

The fog was more sparse in its areal coverage during the initial 3 days of the period — but became more persistent and widespread beginning on 24 November. The arrival of increasing dense middle to upper-level cloud cover on 19 December (associated with an atmospheric river) began to obscure the fog across the northern 2/3 of the Central Valley.

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1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Water Vapor images (above) displayed an intermittent signature of subsidence-induced warming/drying (brighter shades of yellow to orange) that led to the development of strong downslope winds in the Front Range of Colorado on 17 December 2025. Several sites recorded peak wind gusts in excess of 100 mph.

A toggle between a GOES-19 Water Vapor image and Topography (below) showed the signature of subsidence just downwind (east) of the higher elevation of Colorado’s Rocky Mountains.

GOES-19 Visible images (below) highlighted gaps in patches of dense clouds that allowed the subsidence signatures to be seen in Water Vapor imagery.

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Several hours after sunset, GOES-19 Shortwave Infrared images (below) showed the thermal signature associated with a wind-driven grass fire in Yuma County (located in far eastern Colorado) — which prompted the issuance of a Fire Warning that led to evacuations. About and hour prior to the onset of the fire, there was a wind gust to 77 kts (88.6 mph) to the west of Yuma County at Akron — and shortly after the fire began, there was a wind gust to 80 mph at a RAWS site in southeastern Yuma County.

The initial fire detection in GOES-19 Shortwave Infrared imagery appeared to be at 0507 UTC — but until that time, there was a layer of dense cloud cover moving across the area (which masked the view of the surface, so the fire could have started earlier).

The thermal signature of this Yuma County, Colorado grass fire was also very apparent using the Next Generation Fire System (below). As with GOES-19 Shortwave Infrared imagery, the initial NGFS detection for this fire also occurred at 0507 UTC.

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A somewhat unusual feature was visible off of the coast of Wisconsin’s Door Peninsula on 15 December 2025. Bands of clouds were separated by narrow, tight corridors of clear air. Such straight lines are not common for natural features in the atmosphere, which hints that they may be anthropogenic in nature. The highest resolution geostationary view is found in GOES-19 ABI Channel 2, which is nominally 0.5 km at the sub-satellite point. The following animation depicts the evolution of the structure throughout the morning and early afternoon.

One potential explanation for this phenomenon is a set of distrails. Many people are familiar with contrails (short for “condensation trails”), the linear clouds produced from the exhaust of aircraft traveling at high altitudes. A common byproduct of combustion is water vapor, and if a flight is taking place in a saturated layer of the atmosphere, the water vapor produced by the plane’s engines will deposit into ice crystals.

Distrails, short for “dissipation trails,” are effectively the opposite of contrails. Instead of forming when a plane flies through clear sky, distails form as a plane flies through a supercooled liquid cloud. Two separate mechanisms can be at work here: first, the hot exhaust causes evaporation of the existing cloud droplets, and second, the exhaust particles of the aircraft engines serve as condensation nuclei forcing the existing water vapor to condense and precipitate toward the surface. Regardless of the mechanism at work, the end result is a long, narrow region of clear air within an existing cloud.

The day cloud phase distinction RGB can help provide a little more information on this structure, albeit at the cost of worse spatial resolution since we have to bring in the 1-2 km infrared bands to make this product. Here, we see that the preexisting clouds are lavender, which means they are likely lower level liquid clouds. Given the ambient weather conditions in the upper Midwest at this time, it’s all but certain that those are supercooled liquid clouds. An airplane flying through these clouds could easily disturb the saturated equilibrium and force the dissipation of the clouds.

One other valuable tool for this investigation is VIIRS. This polar-orbiting instrument doesn’t have the constant presence of the GOES ABI, but it makes up for it with higher spatial resolution. An overpass from NOAA-20 at 1745 UTC (11:45 AM CST / 12:45 PM EST) was perfectly timed to capture this event in true color.

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10-minute Full Disk scan JMA Himawari-9 AHI Visible, Shortwave Infrared and Infrared Window images (above) showed multiple pulses of pyrocumulonimbus (pyroCb) clouds that were spawned by a large bushfire in southwest Queensland, Australia on 13 December 2025. The pyroCb cloud pulses exhibited a cloud-top 10.4 µm infrared brightness temperature (IRBT) of -40ºC (denoted by darker blue pixels) or colder — a necessary condition to be classified as a pyroCb, since that temperature assured that heterogeneous glaciation had occurred at the cloud top — with some IRBTs of the larger pyroCb clouds in the -65 to -69ºC range (darker shades of green). In addition, note that the pyroCb cloud tops appeared as darker shades of gray in the Shortwave Infrared images, due to enhanced solar reflection off the smaller smoky ice crystals.

Himawari-9 Fire Temperature RGB + Infrared Window images viewed using RealEarth (below) indicated that the large bushfire was burning just south of Durham, Queensland.

According to a plot of rawinsonde data from Charlesville, Queensland at 2300 UTC on 12 December (below) — about 4 hours prior to the initial pyroCb pulse — the coldest pyroCb cloud-top IRBTs in the -65 to -69ºC range were near or just above the Most Unstable (MU) air parcel’s Equilibrium Level (EL), and just above the local tropopause.

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