A recent snowfall and relatively moist airmass in place made for a complicated scene over southern Colorado on 13 Jan 2019. As has been shown in previous blog posts, the Day Cloud Phase Distinction RGB is a great tool for differentiating low clouds (light blue) from snow (green) from high clouds (reds) during the day. In this example, the RGB imagery was utilized to monitor low cloud and fog evolution across much of the CWA in order to keep the grids/forecast accurate, but especially near KPUB, KCOS, and KALS in order to provide accurate TAFs. 1-min imagery was available from one of the GOES-17 default mesoscale sectors to provide even more detailed cloud analysis. Compare the RGB (Fig 1) with VIS (Fig 2). Cloud analysis is much easier in the RGB, particularly in areas where low clouds are present over/next to snow cover.

Note the sharp gradient in snow cover south of the Arkansas River (KPUB to KLHX to KLAA), where northerly flow becomes upslope, aiding the development of snowfall. Near and north of the river to the Palmer Divide, northerly flow is downslope, which limits snow potential in such a case. Snow is apparent again further north along the Palmer Divide from KCOS through KDEN, where northerly flow is upslope again.

Notice the stationary area of relatively high reflectance just south of KPUB? It turns out that is steam emitted from a local Power Plant (Figure 3)!

Bill Line, NWS

GOES-17 data are preliminary and non-operational.