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.

View only this post Read Less

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.

View only this post Read Less

10-minute Full Disk scan GOES-18 (GOES-West) daytime True Color RGB and nighttime Dust RGB images created by Geo2Grid (above) highlighted plumes of glacial silt being transported offshore by strong katabatic winds that were occurring in the northern Alaska panhandle on 09-10 December 2025.  Note the strong pressure gradient between a ridge of high pressure centered inland over Yukon and a consolidating Gale Force Low over the eastern Gulf of Alaska (surface analyses).

GOES-18 Visible images (below) included plots of METAR and RAWS surface reports — which showed that surface air temperatures at high-elevation inland sites were in the -40s F, compared to around +20 F along the coast. The aforementioned pressure gradient between the cold/dense air inland and the warmer/less-dense air near the coast acted to channel winds through valleys and mountain passes (topography), with these winds accelerating as they approached the coast. During the daytime hours, RAWS site DHWA2 (located 62 miles southeast of Yakutat, PAYA) reported a wind gust to 56 mph at 2225 UTC on 09 December — and after sunset, a wind gust to 64 mph at 0225 UTC on 10 December.

A NOAA-21 VIIRS True Color RGB image visualized using RealEarth (below) provided a high-contrast, high-resolution view of the glacial silt plumes as they emerged from the Alaska panhandle coast.

During the following nighttime hours, there was enough illumination from the Moon — which was in its Waning Gibbous phase, at 72% of Full — to provide a faint signature of the glacial silt plumes in a NOAA-21 VIIRS Day/Night Band image (below), as changing winds began to transport them southward (a trend that was also seen in nighttime GOES-18 Dust RGB imagery).

Metop-B Ultra High Resolution ASCAT winds (below) showed the narrow plume of katabatic winds emerging from the coast just southeast of Yakutat (at 59.5 N latitude, 139.5 W longitude) at 0448 UTC on 10 December. The broader area of stronger offshore winds farther to the southeast was masked by cloud cover.

Similar events involving the offshore transport of glacial silt occur from the Copper River Valley in south-central Alaska.

View only this post Read Less

While longtime residents of the Great Lakes region are familiar with lake breezes, their opposite, land breezes can also impact local weather conditions. In the spring and summer, the density difference in the air over the warm land and the cool lake induces a breeze that blows cold air ashore. In the late fall and the early winter, however, that relationship is reversed. The land cools off quickly as polar air masses plunge southward from Canada, but the lakes retain their relative warmth for some time into the winter. This creates a breeze in the opposite direction as air from the cold land surface flows offshore onto the (comparatively) warm lake.

On the morning of 8 December 2025, land breezes from multiple shores of Lake Huron contributed to the development of snow over the lake through the creation of a convergence line in the middle of the lake which fostered enough vertical lift to induce snow. Let’s take a closer look at this case, starting with an animation of GOES-19 Channel 2, the high-resolution visible band. Start by looking at the temperatures: surface temperatures for the shoreline weather stations surrounding the lake are in the low 20s or upper teens Fahrenheit. The lake itself, however, is much warmer as can be seen with the 40 F buoy observation in the middle of the lake. However, even if the buoy were not present, you could still assume that the lake is warmer than the surrounding land as it hasn’t frozen yet and thus must be above 32 F. Thus, conditions that support a land breeze (strong lake-to-land temperature gradient, the absence of strong synoptic forcing) are present. That can also be seen in the surface wind observations. The shoreline weather stations all show westerly flow, even though stations in the center of the state are almost all calm. The weather station on Drummond Island, just to the east of the eastern tip of Michigan’s Upper peninsula, also shows flow oriented toward the lake with a substantially more northerly component than other stations in the area.

However, it’s hard to really see the convergent wind pattern with just a handful of stations on the edge of the lake. This is a sparsely populated region (especially on the Canadian side of the lake) and thus weather observations are rare. Fortunately, there was an ASCAT (Advanced Scatterometer) overpass at roughly this time. Scatterometers measure wind speed by measuring the surface roughness of large bodies of water; stronger winds mean rougher seas and the ASCAT retrieval algorithm can take this roughness and convert it to wind speed and direction. ASCAT instruments are mounted aboard both American and EUMETSAT polar orbiting satellites. While ASCAT winds don’t have the temporal continuity of a geostationary product, the fact that multiple polar orbiting satellites are available means that midlatitude locations are observed somewhat regularly with these systems.

In this particular case, the convergence pattern could hardly be clearer: flow from the lower peninsula of Michigan is largely westerly while flow from Ontario is largely northerly. Where they meet, a line of clouds has formed. These clouds are largely held in place by the opposing winds, and thus the cloud band doesn’t propagate ashore.

Of course, RGB images can help us better interpret what is happening in this environment. The following animation shows the Day Cloud Phase Distinction RGB for this scene. There are a few interesting things to see in this view. One is the clear demarcation of surface snow (green) from the ice clouds passing overhead (red). Of greater interest to this current discussion, however, is the change of color in the cloud band over the middle of the lake. Where the convergence pattern is weaker the clouds are not as vertical and thus they tend to be warmer, liquid clouds that show up as lavender. However, where the convergence pattern is more robust, the resulting clouds are deeper and changing phase into ice clouds. This appears as the yellow-green clouds in the animation.

Finally, with all this vertical growth taking place, is it precipitating? The Multi-Radar / Multi-Sensor System (MRMS) is a good tool for this task as it integrates both United States and Canadian radars into a unified radar mosaic product. These lake-impacted cloud events tend to be shallow, and the standard NWS radars may be too far away to clearly identify what is happening. However, MRMS clearly shows the development of precipitation. Given that these are ice clouds and the surface temperatures are well-below freezing, it is almost certain that this cloud band is producing snow.

View only this post Read Less