I have Bipolar I. Cooler weather would start out nice--less agitation for some reason--but sometimes I'd dip into depression (sometimes psychotic depression, which always requires some sort of drug treatment). Anyway, since I've been doing the Orthomolecular Medicine thing (the core is lots of niacinamide+b-100+c+e+other things you might need, like D3), my mood has been much more stable, even now that the weather is getting cooler. I also get more mileage out of my "don't go nuts" pills. I'm down to 2--Abilify plus a non-addictive, sedating "mood stabilizer" (glorified sedative, really). Lots of people with Bipolar I, especially when there's recurrent, psychotic depression onboard, require far more meds.
Just a thought. There's also fish oil, Omega 3-6-9, SAM-e, 5-HTP, and St.John's Wort to consider as alternatives to an Rx mood elevator (although I'm sure you can take some supplements w/ the antidepressant). A light box is an excellent idea.