A big push for the VIIRS Front Range collaboration is to evaluate the VIIRS day-night band products as part of a JPSS Proving Ground evaluation. In the overnight hours of July 21, the conditions were favorable to use the reflectance product (using reflected moonlight) which requires both a near full moon as well as the moon being over the horizon. There were several interesting features to observe with the VIIRS overpass at 0821 UTC on 21 July in and around the Boulder and Cheyenne county warning areas. Figure 1 kicks off with the VIIRS reflectance product. The conditions were very favorable for using the reflectance product (just one day before the full moon and the moon was over the horizon) and provides a nighttime display of the region with almost visible imagery quality. Since the day-night band is a low-light sensor, it also observes lights from cities (Denver and Cheyenne are pointed out). This image also shows some shadows cast by the clouds. Also, there is an interesting curved cloud feature in eastern Colorado and into western Kansas, circled in yellow.
I wanted to compare the reflectance product to the high-resolution IR imagery in Figure 2. The coldest tops in the northeast show up very well. The circled feature further south does not show up, supporting that this feature is a low-level feature.
To further investigate this we can use the VIIRS radiance RGB composite in Figure 3. Here, a couple features stand out. First, given the favorable conditions with the moon, the RGB is more useful in identifying low and high clouds compared to several nights ago. In this image, the blue clouds are the highest clouds, which correspond well to the coldest tops seen in the IR. Also, the interesting cloud feature circled stands out in yellow, signifying a low cloud feature. Again, the city lights are seen in this channel and appear yellow. Also, a feature that Rob Cox (SOO – Cheyenne) pointed out in an evaluation a few days ago, several lightning flashes are observed. I attempted to see if the Colorado Lightning Mapping Array observed the flashes, but this was too distant from the network.
Lastly, in Figure 4, we go back to the nighttime microphysics RGB which helps reinforce what we have been observing earlier. The thick, high clouds discussed earlier show up as red, while the interesting feature circled stands out clearly as low clouds as shown by the radiance RGB as well. Also, another small low cloud feature is seen coming off the storm system in the northeast, which may be a developing outflow.