My most accurate forecast comes from a friend who flies... he's got some site that he gets on (might be NOAA), and he can actually read the maps and tell what's going on and why... pretty interesting to watch him.
For my daily use, I prefer Intellicast's "graph" format... the site defaults to "table" but you can change it. Allows me to figure out that a daily 30% of rain really means 80% at 2PM or whatever, and I can customize the graph to factor in humidity, wind direction, etc.. I'm a hunter, and where I live, March and June/July/August are the only months I can't hunt something, and I don't like being out in June-August here in LA anyway... the forecast is typically "High in the mid 90s, low in the mid 70s, 30% chance of afternoon thunderstorms" during those months. That's why a lot of guys fish then.
When I'm out for more than a few days, some sort of instinct kicks in again, and I can just tell what's going to happen in the next 6, 12, or 24 hours, in a general way, by the wind and humidity mostly. Humidity goes way up and the wind shifts to the south before it rains. Fog in the morning is a good sign. Red sunset usually bodes well. Red sunrise means bring a poncho along that day. Cirrus clouds mean clear, dry weather and cooler temps...
When I lived up North I could tell when it was going to snow too, by the clouds... there's just a low, grey overcast, along with a certain wind and temp that means snow... can't really explain that one. anyone who lives up there can probably do it.
On a related note, I pay WAY more attention to the moon phase, sunrise/set times, and position of various planets when I'm out for more than an overnighter... helps you stay found, I guess...