The fluorescent lights in my kitchen, do not work when the temps are 30 or below. Above the kitchen is my bedroom, it is well heated. I also have a regular ceiling light in the same kitchen. It hangs from the ceiling it comes on fine. The fluorescent lights are flush to the ceiling. Not a problem if there is not a long cold snap. But if the temps are in the twenties for extended days then no bright lights. What can I do?

Two things. It appears that the rim joist between levels wasn't insulated, so you have an area which is subject to outside weather, especially when windy. Unless you plan to tear up some flooring there isn't much you can do with this. However, there are low temperature ballasts available for many fluorescent fixtures, especially the newer electronic type which work down into the freezing temperatures. I suspect you may have to change the fixture.

MB is correct. Older style magnetic ballasts will not work at low temps. Get a newer light that uses an electronic ballast. If you can get access to the space after removing the light, start stuffing some loose fiberglass in there.