Most urbanites won't. That's what the TV weatherman is for (who I think just regurgatates the NOAA forcasts). Plus, it's kinda hard to read the sky with all those buildings in the way. <img src="/images/graemlins/smile.gif" alt="" /> At least here in Florida, once our "rainy season" starts, you don't need to look at the sky, just look at your watch. They will start everyday at the same time (+/- 5 minutes). It's kinda cool.
My personally, I notice the "Red sky in morning, sailor take warning" and the "Red sky at night, sailors delight". But, that's only because my dad taught me that saying.