Are you getting the valley fog with a vengeance?
Playing here in Berkeley, if we show up at 11AM, the fog is so thick we can't clearly see two courts off to the side, and high lobs have the fog completely hiding the ball. We CAN see our opponent's, so it's not that bad.
Then at noon, the fog magically shifts, the sun comes out, and it's pure blinded overheads with some really dark shadows from the tall cyprus trees.
Before the end of the third doubles sets, the fog returns and everyone scampers to put on their jackets and long pants, the the courts start to get wet and slippery again.