NCC monitoring severe weather during the nighttime
Monitoring severe weather during the nighttime can be challenging since GOES-16/17 is limited to infrared imagery during the overnight hours. In complement to geostationary data sets, polar-orbiting satellite data can be utilized, specifically the Near-Constant Contrast (NCC) product.
For unfamiliar readers, NCC is a derived product of the Day/Night Band (DNB) that utilizes a sun/moon reflectance model that illuminates atmospheric features and senses emitted (e.g. lights from lightning, fires, city lights) and reflected (e.g. clouds) light sources during the nighttime. The product is considered ‘nighttime visible’ imagery that looks very similar to 0.64μm visible imagery that forecasters use during the daytime. Now NCC also has its limitations, since it is dependent on the lunar phase (i.e. full moon compared to new moon) and moon elevation angle (i.e. the moon position above or below the horizon). NCC imagery can range in texture, varying from ‘crisp and clear’ imagery to ‘fuzzy and non-conspicuous’ imagery depending upon the lunar phase and moon elevation angle. NCC is at 0.7µm, exhibiting a 750-m spatial resolution.
NCC observed severe weather over the southern United States during the early morning hours of 18 April 2019. Severe weather was experienced in several states: Texas, Oklahoma, Arkansas, Louisiana and Mississippi. The NCC and GOES-16 infrared imagery (seen below) observed severe weather in the forms of convective cloud tops (i.e. very cold brightness temperatures), lightning, cloud cover and emitted lights from cities. Imagery is taken at ~0800 UTC on 18 April 2019, where NCC imagery is seen during the full moon phase of the lunar cycle. Notice in the NCC, the lightning that is observed via horizontal white streaks. The white streaks are due to the time discontinuity between the lightning strike (i.e. on the order of milliseconds) and the satellite overpass (i.e. on the order of seconds).
NCC at 0759 UTC, 18 April 2019 – Nighttime Visible Imagery
GOES-16 10.35μm at 0801 UTC, 18 April 2019 – Infrared imagery
The Geostationary Lightning Mapper (GLM) (seen below at the same timestamp) is also used in complement to NCC, in identifying where the high density lightning strikes are observed within the line of storms (red dots); it matches up quite well with NCC. Note, GLM is overlaid onto GOES-16 10.35μm.
GLM at 0801 UTC, 18 April 2019 – Group Flash Counts Density (via CIRA SLIDER)
