CSFF
I Quote....
"Takeoff with light coatings of cold-soaked fuel frost on upper wing
surfaces is allowable, provided the following conditions are met:
• the frost on the upper surface is less than 1/16 inch (1.5 mm)
in thickness
• the extent of the frost is similar on both wings
• the frost is on or between the black lines defining the
allowable cold-soaked fuel frost area (see figure) with no ice
or frost on the leading edges or control surfaces
• the ambient air temperature is above freezing (0°C, 32°F)
• there is no precipitation or visible moisture (rain, snow, drizzle
or fog with less than 1 mile visibility, etc.)"
from a Boeing Manual.
The picture shows that the icing in question does not meet the above criteria and it is a little disappointing to say the least that the crew did not de ice.
The effect of fresh snow falling on the "allowable area" would cause it to stick more to this area, hence the limitation above " no precipitation etc.." which was overlooked by the crew it would seem.
Best to keep it simple....