I believe SH3WeatherGen only randomizes the weather settings at the start of your patrol, so if it sets WeatherRndInterval to a high number, you will not get very many changes in your weather pattern until you start a new patrol or reload SH3Weather. This can lead to those 14 consecutive days or more of stormy weather where you can't see or sink anything.
Without knowing what numbers SH3Weather assigns to the WeatherRndInterval parameter, I like setting it manually to the settings I have discussed, because I think it gives me more variety in the weather during any given patrol.
BTW, my posts are not meant to be a put-down of SH3Weather in any way. It's still a great program and light years better than anything I could come up with--especially for those who are not comfortable mucking about with game text files. Cheers!