I have now completed three full patrols with this, two to the Freetown area, one to the east coast of the USA, all in 1943-44. These were proper patrols to continue a complete campaign (see below).
This fix appears to work perfectly with NYGM. It functions by controlling the clouds and fog parameters with counters.
It has been interesting to compare this fix with the weather fix that I made which controls the windspeed, and which I have been using for a long campaign with NYGM (1939-1943). The windspeed fix controls the buggy wind force with subtraction of 15 m/s when the wind is too high, and with a counter if winds of 15 m/s or more are encountered too often.
H.sie's cloud/fog fix is very effective at controlling these parameters, but not the wind, except indirectly. The windspeed fix controls the wind, but not the clouds and fog (except indirectly). The result is that the weather is more varied with the windspeed fix, but there are fewer 'foggy-storms' with the clouds fix.
There was just one continuous period of eight days of 'foggy-storm' off the USA in my patrols with the H.sie fix (two days with 15 m/s winds, medium visibility; six days with 15 m/s winds, heavy rain, heavy fog). However, this added useful variety, and it never recurred during my three long test patrols.
In case anyone wants to compare the windspeed fix with H.sie's clouds fix, I have updated the link for the winds fix here:
http://www.subsim.com/mods1/nygm/Stiebler_EnvSim.7z
However, my own preference is for H.sie's mod!
[To anticipate the obvious suggestion:
H.sie and I both agreed that the combination of a windspeed and clouds fix created far too much good weather.]
Stiebler.