100 degrees is the recommended maximum, including the surface temperature of your siding.
Does that mean we can’t paint on days when the temperature exceeds 100 degrees? We still can because there are ways to compensate for the heat. For example, we can start early in the morning and quitting earlier in the afternoon before it gets that hot. We also paint on the shady side of the house. That way we are not in direct sunlight as that will raise the surface temperature above 100 degrees. We start on the west side in the morning and work our way clockwise around the house so we are always in the shade.
Even when the temperature is in the 90’s getting a good coat on can be difficult. If the paint dries before doing the next section those two sections won’t blend together unless they are both wet. We can compensate for this by using Latex Extender or Flotroll which slows down the drying time to keep one section wet long enough for the painter to move his ladder to the next section.
In the colder months we use paint designed to be applied down to 35 degrees. I don’t like to paint unless it’s going to stay above 40 degrees for at least 2 hours after we are done spraying.
In any given month during the winter in the Tri-Cities there will be a few days when it will be above 40 degrees for 4 hours or so. This is usually between 11 am and 4 pm. During that time it is possible to get some painting done in the winter. That said, if I have interior work to do I’d rather be doing that in the middle of the winter rather than working with a slim to non-existent window of opportunity with an exterior.