Water clouds with small droplets on the cloud top

Fog and water clouds with small droplets on the cloud top appear white in the Snow RGB images.

The images below show situations when fog and/or low clouds formed over the snow covered surface. The valley fog or stratus clouds are nicely seen in the Alps due to the good colour contrast between the red-orange snow and the white water clouds.

Meteosat, SEVIRI Snow RGB, 08 January 2009, 09:55 UTC

Meteosat, SEVIRI Snow RGB for 15 January 2006 10:55 UTC

Continental fog and low level water clouds usually consist of small droplets. Note that water clouds with large droplets on their top appear not white, but light yellow in the Snow RGB images.

Explanation of the colours for fog and water clouds consisting of small droplets (see the recipe):

• The reflectivity values of water clouds are high in the VIS0.8 channel, lower in the NIR1.6 channel and even lower at 3.9 micrometer channel. However, after the linear stretching and the gamma correction the signal will be very high in all three colour beams. The green signal is often saturated; the blue signal is also often close to the maximum. As a consequence water clouds with small droplets appear (close to) white in the Snow RGB images.