Dissolution can be used in a number of different ways: https://www.merriam-webster.com/dictionary/dissolution I think that, in this case, the writer means: the end of November, or the closing out of November (the last few days). They're talking about it getting darker, more sombre, the days are shortening and the weather is getting worse - cloudy, rainy, etc (grey). I think the writer is deliberately using two meanings. The ending of November/autumn, and dissolving into winter.