Depending on various factors including how much scientific training one has, what strikes one person as obvious may be difficult to understand for another. In science, it's almost never easy to get an instrument to measure exactly what you want.
Case in point: Sea ice concentration. Some of the best instruments are on the
AMSR-E/2 satellites. Due to physics, data from the high frequency channel, which is used as input to sea ice concentration algorithms, is
sensitive to water vapor and clouds. One result of this is that the Bremen concentration maps typically show high concentration ice in areas covered by cloud, regardless of the actual ice concentration.
In fact, even without knowing any technical details, it's easy to see this effect by looking at consecutive days, e.g. using gifs. Large obvious cloud artifacts (purple in the NIC color scheme) frequently appear. These artifacts typically don't persist for many days (except some areas do remain cloudy for weeks on end) and are not predictive of ice edge changes. E.g. Look at the righthand map on the gifs in
this post.
In short: Bremen concentration maps from a cloudy days are almost useless. The most recent one (Aug. 10) is a good example. I've attached a fade-across gif of Aug. 9 to 10; originals, right; 5-day median, left. The huge purple area that suddenly covers (e.g.) the asian side is obviously due to cloud. If you have any doubts, cross reference the satellite images, also attached (ice under clear sky is dark red).
I.e., It is counter-productive to cherry-pick cloudy days in an attempt to show concentration increases (or similarly, area).
Click to animate top gif.