One other thing to keep in mind... with the exception of some rare phenomena, "atmospheric conditions" are going to INCREASE propagation distances rather than decreasing them. Further, these events will typically last hours rather than days, especially in the high VHF range, as opposed to the very atmospherically dependant HF range.
As Dave has correctly pointed out, this sounds more like an "external condition" than the atmosphere. The variability from day to day is yet another pointer to some man-made issue.
--Sean