I use one of these too.  Point of clarification though:

IR is very useful to detect clouds but not rain. If all you want is to close when it's cloudy that will work for sure. What you want is a seasonally-dependent *difference* between air temp and IR sky temp. The actual sky temp varies too much for a single threshold to work.

But the real bugaboo is rain. Failing to close when it's cloudy is no big deal. You just have some bad subs to delete. Failing to close when it's raining can destroy your expensive equipment.  IR doesn't help you here except that closing when its cloudy will usually mean you're still closed when it starts pouring.

But you should also look into a rain sensor in addition to a cloud sensor. These work by either detecting moisture using electrical conductivity of a metal grid (most also include a heater to prevent corrosion after the rain stops), or an optical sensor that actually "sees" the drops on a lens.