10-minute Full Disk scan GOES-18 (GOES-West) Infrared and Water Vapor images (above) showed the evolution of a mountain wave cloud south of the Brooks Range in northern Alaska on 01 March 2026. The coldest cloud-top infrared brightness temperatures were -61C (darker shades of red).

A toggle between GOES-18 Water Vapor and Infrared images at 1200 UTC (below) included a Topography image and 700 hPa wind barbs from the GFS model — which showed northerly winds flowing across the terrain of the Brooks Range, with the mountain wave cloud displaced to the south.

A toggle between GOES-18 Infrared and Water Vapor images at 1800 UTC (below) included an image of 500 hPa Vertical Velocity — the bulk of the mountain wave cloud was co-located with the zone of middle-tropospheric upward vertical velocity (brighter shades of green).

A Suomi-NPP VIIRS Infrared image (below) displayed the mountain wave cloud at 1402 UTC. This cloud appeared to play a role in keeping the surface air temperature at Fort Yukon (PFYU) significantly warmer than surrounding sites (by limiting radiational cooling across the Yukon Flats).

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5-minute CONUS Sector GOES-19 (GOES-East) Near-Infrared “Snow Ice” images along with Radar Reflectivity images (above) showed a band of clouds producing precipitation that was moving southward across the North Dakota/Minnesota border region on 27 February 2026. Moderate to heavy snow produced by this feature — along with blowing snow created by strong winds — prompted the issuance of a Snow Squall Warning at 2008 UTC that included a portion of Interstate 29 in the vicinity of Grand Forks (2011 UTC GOES-19 image). Peak wind gusts reached 51 kts (59 mph) at Grand Forks ND (KGFK), and the surface visibility was reduced to less than 1/4 mile with heavy snow at Crookston MN (KCKN).

Day Snow-Fog RGB images created using Geo2Grid (below) displayed the southward progression of this cloud band (brighter shades of white: 2011 UTC image) — as well as narrow northwest-to-southeast oriented horizontal convective rolls (a signature that highlights areas where significant blowing snow is occurring) in the wake of the cloud band responsible for the Snow Squall Warning. Areas of snow cover exhibited brighter shades of red.

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A narrow, but intense snow band formed over an area stretching from central Iowa to southwestern Wisconsin over the the night of 19 February into the morning of 20 February. Localized accumulations reached a foot in parts of northeast Iowa. This map from the La Crosse, WI, National Weather Service office shows the extent of this snowfall. (A lengthier discussion of this event from NWS La Crosse is available here).

A week later, this narrow corridor of snow is still around and still exerting influence on local weather conditions. Take a look at the following plot of surface temperatures from AWIPS in the early afternoon of 27 February 2026. North-central Iowa is experiencing temperatures in the lower 60s while parts of eastern Iowa are even reaching 70. However, there’s a cooler alley in northeastern iowa where temperatures are in the low-to-mid 40s.

Without any context, an analyst might opt to put some sort of synoptic-scale feature in northeast Iowa and assume that larger-scale flow is causing this pool of cooler temperatures. However, this being the CIMSS Satellite Blog, we’re going to recommend that you check out contemporaneous satellite imagery to verify what might be happening. Here’s the same figure, this time with the 0.64 micron highest resolution satellite imagery included as the base layer.

It’s clear that the surface snow cover is exerting a downward influence on temperatures. But why? There are two main reasons. The first is that snow has a high shortwave albedo: it reflects a substantial fraction of the light that shines on it. The albedo of new fallen snow can be as high as 90%, thoough for older snow such as this it’s much closer to 40 or 50%. Still, that is a substantial fraction of the incoming solar heating that is redirected away from the surface and cannot help to change the temperature. The other impact of snow is through phase changes. The solar energy that isn’t reflected from by the snow goes into changing its phase through melting or sublimation.

Here’s a pair of animations captured from AWIPS (thus the color dithering is not ideal). The first shows the true color RGB with the surface temperatures, while the second depicts the Day Cloud Phase Distinction RGB. Both are useful for identifying the location of the snow band surrounded by bare ground, while the latter animation helps discriminate between the snow (green) and ice clouds aloft (pink).

Finally, we should also take a look at the impact of the snow band on nighttime temperatures. While the earth’s surface generally has very high infrared emissivities, surface snow has a near perfect emissivity up to 0.99. This means that the snow is a very effective emitter of infrared radiation, more so than other surface types. Thus, we expect snow-covered ground to be colder at night than uncovered ground. This, of course, is on top of the fact that the snow-covered ground didn’t get as warm during the day as the other locations did, so it’s already starting from a lower temperature. This image shows the Band 13 (10.35 micron) imagery for 12:40 AM on the 27th. The color table has been adjusted to enhance contrast. Recall that for this window channel, in the absence of clouds we’re reading the brightness temperature of the surface. That surface is colder where the snow is, and the surface temperature observations back that up.

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5-minute CONUS Sector GOES-19 (GOES-East) True Color RGB images created using Geo2Grid (above) showed aircraft glaciation trails drifting east-southeastward over southern Lake Michigan on 25 February 2026. As aircraft ascended/descended through a thin cloud layer composed of supercooled water droplets, additional cooling from wake turbulence (reference) — and/or particles from jet engine exhaust acting as ice condensation nuclei — caused the small supercooled water cloud droplets to transform into larger ice crystals (many of which then fell from the cloud layer as snow).

GOES-19 Day Cloud Phase Distinction RGB images (below) revealed that the cloud layer which the aircraft penetrated was composed of supercooled water droplets (shades of violet to purple) — while the ice crystal aircraft glaciation trails exhibited shades of green.

Cursor samples of the GOES-19 Cloud Top Temperature (CTT) derived product at 2 locations along the undisturbed supercooled water droplet cloud between aircraft glaciation trails (below) showed that while those CTT values were quite cold, they were still a few degrees warmer than the -40ºC temperature required to assure spontaneous freezing via homogeneous nucleation.

In a comparison of GOES-19 Shortwave Infrared brightness temperatures over an undisturbed portion of the supercooled water droplet cloud vs within an aircraft glaciation trail (below), enhanced solar reflection off the small spherical supercooled droplets produced a 3.9 µm temperature that was about 11ºC warmer than that of the ice crystals within a glaciation trail.

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