The nighttime microphysics (NTmicro) RGB comparison below provides some insight into the traditionally difficult challenge of differentiating low clouds from fog. The RGB product enhances the regularly employed 10.8-3.9 channel difference (Green) to include an additional 12.0-10.8 channel difference (Red) and repeat use of the 10.8 thermal channel (Blue). The NTmicro RGB valid at 311am MDT on October 17, 2013 showed an area of cloud cover developing in the Pecos River Valley from Carlsbad north to Artesia and just east of Roswell (aqua shades). Observations within this cloud cover indicated a low cloud deck developing toward the north with ceilings in the 1,500-2,000′ level. The hybrid 11-3.9 imagery indicated the low clouds continuing to expand north toward Roswell through 11Z (yellow areas). The aviation forecaster anticipated that low clouds would move into Roswell and thus amended the TAF to include IFR ceilings for several hours. Fog was not added to the TAF however a brief period was observed. The NTmicro RGB valid the following day at 251am MDT on October 18, 2013 showed a significantly more widespread area of cloud cover impacting much of southeast NM and the Permian Basin of west TX (purple shades). Observations within this cloud cover indicated a very low cloud deck of 100-200′ and numerous reports of fog. The hybrid 11-3.9 imagery indicated the low clouds were expanding north toward Roswell however remaining to the east of the site through 12Z (yellow areas). The aviation forecaster did not expect fog and/or low clouds to impact Roswell based on this imagery and the clear sky forecast was maintained. Without the support of observations across the region on the 18th the forecaster may have been able to distinguish shallow/thin fog from the low clouds on the 17th. The green contribution has been reduced because the 3.9micron channel is seeing some emission from not only the shallow/thin fog but the surface as well. The 3.9 channel is thus warmer and the difference from the 10.8 channel is less, resulting in less green color. Greater amounts of red and blue lead to the strong purple shades.