There is a whole mess of good sites out there on the subject. See for example:
My point of this is that I predict that next weekend (16-17 Oct 2010) it will be a clear weekend, or at least no rain! Why? Well cyclogenesis typically creates a cyclonic disturbance and it takes 4-7 days. That means we get into a cycle of having rain (or snow) every weekend or during the middle of the week or what ever. We get into a "cycle" of having the same kind of weather on the same days of the week. That is, until the cycle is broken. Stay tuned.