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Polish final report on Smoleńsk aircrash [853]
So, Smolensk weather on April 10, 2010 between at Polish times, 5 and 11 AM:
5:00 AM - Poland time (corresponds to 7 AM Smolensk time - and 04 AM London time) -- Mist with 4 km visibility
6:41 AM - Poland time (corresponds to 8:41 AM Smolensk time - and 05:41 AM London time) -- Heavy fog with 400 m visibility) - Crash happend at this time..
8:00 AM - Poland time (corresponds to 10 AM Smolensk time - and 07 AM London time) -- Heavy fog with 500 m visibility
11:00 AM - Poland time (corresponds to 1 PM Smolensk time - and 10 AM London time) -- Mist 4 km visibility
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We don't know at what time the minimum visibility was. With an interpolation in this weather data based on time, it is likely between 05:30 and 07:30 Polish times. I suppose minimum visibility was before 06:41, maybe, it was 200 m then and it is logical due to sunlights effect (before 8:41 smolensk time.) So, fog was heavier before 6:41, maybe, it was around 5:30- 6 AM when Yak was on Smolensk airport..
Between 6:41 and 8 AM, visibility change is 100 meters only. Since outside effects such as storms etc didn't exist there, it was a kind of stagnant or laminer flow, or slow process, with no sudden changes. So, change in moist/fog is more or less linear change except at around critical point of phase change which likely took a minute or two. So, assuming minimum visibility 400 m was at 6:41, then, at 5:41, visibility was again 500 m.. Again, 5:41 was the time when Yak was at Smolensk airport.. Except those critical minute or two, change in the weather took at least 2-3 hours, between 5 and 8-9 AM polish time. One hour of this change, which was enough to forecast coming fog was before crash time.
So, Yak definitely knew it was heavy fog and Yak crew should have informed urgently.. But, we don't hear anything, any such urgent communication between Yak crew and Warsaw controller..