A winter storm brought snowfall to much of southern Colorado on 11 November 2018. Behind the storm system on the 12th, a variety of low and high clouds lingered during the day after the snowfall had ended. Interrogating visible satellite imagery alone, it is difficult to differentiate the clouds from surface snow cover given both are highly reflective. The additional bands on the GOES-16 ABI compared to previous GOES imagers allows for the creation of RGB combinations that help differentiate various clouds from each other and from snow. This especially relevant to aviation forecasting when monitoring cloud cover near TAF sites.
The Day Cloud Phase Distinction has been described for this purpose in previous blog posts. The scene on the 12th was another great example of the advantages of using the Day Cloud Phase Distinction RGB over visible imagery alone. In the visible imagery (Fig 1), while it is apparent that there is widespread snow cover with clouds moving overhead, it is difficult to quickly diagnose clouds vs snow. The RGB (Fig 2) makes it clear where there is bare ground (dark blue), snow (green), liquid clouds (light blue), and ice clouds (red).
The Day Snow-Fog RGB can also be utilized for differentiating snow from low clouds and high clouds (Fig 3), but does not provide useful information over the Day Cloud Phase Distinction RGB. Further, it does not utilize the 0.64 um 500 m band, so it lacks the detail that is inherent in the Day Cloud Phase Distinction RGB, which does utilize the high resolution visible band.
Figure 4 provides a comparison of the visible channel with the two RGBs discussed along with labels for the various cloud and surface types.
Bill Line, NWS