VIIRS RGB Night-Time Microphysics Makes the Most of Limited Darkness in Alaska

Despite the hours of darkness becoming rare over Alaska as the northern hemisphere approaches its summer solstice, the RGB Night-Time Microphysics product still has some utility in Alaska south of the Arctic Circle right around midnight. Just before midnight Alaska Time on May 6, 2014 (0743 UTC, May 7) an RGB NT Micro image derived from the SNPP VIIRS instrument depicted a deck of moderately low marine stratus clouds over the northeastern Bering Sea, as outlined in the black box in Figure 1.

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Figure 1: RGB NT Micro product derived from VIIRS data, 1143pm Alaska Daylight Time May 6, 2014. Area of interest noted in the black box.

A closer view of this area is shown in Figure 2, along with the ceiling and visibility data from surface observing sites. In this scenario, ceilings, rather than visibility, are the problematic weather element, with the exception of Nome where the imagery shows a localized area of higher conditions. It can be challenging to discern ceilings and visibilities from satellite imagery, and in this respect the RGB NT Micro product has an advantage over conventional satellite imagery. Per the Quick Guide available at http://weather.msfc.nasa.gov/sport/training/rgb_ntmicro/RGB%20Night-time%20Microphysics%20Reference%20Guide%20AK%20by%20SPoRT.pdf and as demonstrated in the Alaskan training module http://weather.msfc.nasa.gov/sport/training/aviationForecasting_Alaska/launcher.html a tan to light green appearance indicates low clouds, but not necessarily fog, in colder climate regions such as Alaska. Surface observations on Saint Lawrence Island and in the Yukon Delta area indicate MVFR ceilings of between one and three thousand feet, but no reduction to visibility due to fog.

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Figure2 : the same RGB NT Micro product as in Figure 1, zoomed into the northeastern Bering Sea. Ceiling and visibility data from surface observation sites are also shown in green.

One thought on “VIIRS RGB Night-Time Microphysics Makes the Most of Limited Darkness in Alaska

  1. This is great…thanks for posting! Similar colors can be used as an indicator of homogenous cloud types in locations without ground observations. This type of imagery can certainly be useful in that type of application. Also, thanks for posting to the learning modules!

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