i just came back from meadow vista. it's been really cold there at night and it didn't warm up all that much during the day. it could be that the bees are not moving around enough to go to the food. you can make sure that you have honey frames next to the bees and you can put dry sugar moistened with a bit of water on the inner cover. looks like you'll be around 50 degrees tomorrow. you can probably make changes then if you don't spend to much time at it. also, are your bees where they get the sun during the day? it would be tempting with the hot summers to put them in the shade, but in the winter, they need that sun on the hive to warm up enough to break cluster and eat, etc.