I’ve posted about this a few times, but this morning offered another good example of the ability of the Suomi NPP VIIRS Day-Night Band RGB imagery to show low clouds beneath thin cirrus. First, take a look at the 11-3.9 µm imagery (with the standard color curve) from the VIIRS instrument, valid this morning at approx 0749 UTC. Focus your attention mainly over southern Texas.
In the image above, high, cirrus clouds will appear as blue colors, while lower clouds appear yellow. Notice the bank of low clouds in the northern Gulf extending into portions of extreme SE Texas and southern Louisiana. Notice that some low clouds can also be observed in and around the thin cirrus to the southwest in southern Texas. These cloud features show up arguably better in the VIIRS Day-Night Band image from the same time (image 2).
With the Nighttime Microphysics RGB, the low clouds appear as an off-white, while the high thin cirrus are the deep reds and blues spreading across much of the CONUS in the image. Notice the low clouds in southern Texas still cannot be observed very well beneath the cirrus canopy, as the cirrus are mostly opaque to the longer IR wavelengths. Now, let’s take a look at the VIIRS Day-Night Band imagery. I like the Day-Night Band Radiance RGB best for this particular situation (image 3).
Since the cirrus are mostly translucent in the visible portion of the spectrum, the low clouds can be seen beneath. Also, given that the Day-Night Band Radiance RGB has an IR component, this results in better delineation between high and low clouds. In this situation, forecasters would have a much better idea of the extent of the low cloud deck. Observations from 0800Z indicated the cloud bases were around 1-2 kft in that area of southern Texas, which could have significant impacts on sensible weather and forecasts, especially for aviation.