Constant rain in LA area

I would imagine this is related to REX, but I'm not sure. You see, every time recently that I've started a flight in the LA area with REX real-time weather (so far at KLAX and KSMO), it's raining. The odd thing is that it hasn't been raining here, and even when I check the REX weather engine, it doesn't show any precipitation. Perhaps the most bizarre thing is that there are no rain clouds--the rain is falling out of empty sky.Thanks,boeing247