FC level is based on CYA, not weather. Chlorine will likely burn off more slowly in the off season, so you can probably get away with less frequent dosing (I do). But lurking around your FC minimum is risky, even in cooler weather. Remember, chlorine is used up by the sun, yes, but also by the organics that enter your water (that's its primary mission, after all). So while you might be able to rely on consistent weather, you can't rely on never having any errant FC-consuming events occurring, like leaves falling in the water, or bugs, or animals drowning, etc.
If you dose just once a week, it's likely that you're ignoring your pool for much, or all, of that week, too. If something crawls in your water on day 1 after dosing, and drowns in your skimmer, then it could tank your FC in a matter of days, leaving your pool FC free and susceptible. So you decide for yourself the amount of risk you want to take: how often you check your pool and equipment, how often you test, how often you dose...
One of the easiest pool tasks is a simple "drive by." Walk by your pad, look for leaks, listen for the pump running, glance at your filter gauge, then walk by the pool, check that the water is clear, peek into the skimmer. That's it, less than a minute. That's nothing compared to battling an algae outbreak, which can take hours and hours!
Want to play it safe? Mid week, dump in half your normal weekly dose of chlorine. If you're getting consistent numbers each week, it's a safe bet that dosing half the normal amount is going to be fine. You don't have to test. When it comes to chlorine, an extra cup or two will do nothing harmful, and will likely just be supplementing what has already burned off in those first few days. Then come week's end, you'll be much better off, FC-level-wise, than you would have been. That might add a minute to your "drive by" for just that one mid-week day!
