Why visibility suddenly to 1 hex?

[vionville]

But should that dust/fog effect be connected with a storm? If the weather data doesn't contain any value for storm, does that mean there is no possiblity for storm, or storm would happen for a random probability?

I now try it with a human vs human game (default scenario west germany invaded) with programe weather on. This time same problem returns, as visibility worsen on 15.00 (to 2 hexes). Before it could further worsen on, the dusk turn arrived, so the visibility down to 1 hex anyway.

This time obviously there is no problem with "no weather data avaiable", as this is a local game, not email one. So why it doesn't follow weather data?

The weather data for default scenario, you could see aaron's botb weather data is pratically a copy from original one, just change 1985 to 1989.

10 6 1985 80 20 0 0 0 3 5
11 6 1985 100 0 0 0 0 3 4
12 6 1985 100 0 0 0 0 4 5
13 6 1985 100 0 0 0 0 4 5
14 6 1985 100 0 0 0 0 4 5
15 6 1985 80 20 0 0 0 2 4
16 6 1985 100 0 0 0 0 3 4
17 6 1985 100 0 0 0 0 2 3
18 6 1985 100 0 0 0 0 2 3
19 6 1985 70 30 0 0 0 1 2
20 6 1985 70 30 0 0 0 1 3
21 6 1985 60 40 0 0 0 2 3
22 6 1985 30 60 10 0 0 3 4
23 6 1985 40 60 0 0 0 4 5
24 6 1985 80 20 0 0 0 3 4
25 6 1985 100 0 0 0 0 4 5
26 6 1985 90 10 0 0 0 3 4
27 6 1985 95 5 0 0 0 4 5
28 6 1985 100 0 0 0 0 2 4
29 6 1985 100 0 0 0 0 2 3
30 6 1985 90 10 0 0 0 2 3
1 7 1985 80 20 0 0 0 2 3
2 7 1985 100 0 0 0 0 2 3