There are several ways to get weather forecasts on the Internet. Some are those of the National Weather Service, though the best place I've found to access these is at www.wunderground.com. That site makes no bones about what they're issuing, whereas some sites dress up the NWS proclamations to look like their own, proprietary forecasts.
Other predictions come from private firms, like AccuWeather and Intellicast that supply info to TV and radio news broadcasts, newspaper and various industries that need more specific weather data than NWS provides. The private firms are probably more useful to their clients but, on the 'net, the NWS has a big edge. They update info more often and what you get from them is actually written by a human being, as opposed to being output from a computer reading.
Case in point: Right now, it's mostly clear in Los Angeles. The rain stopped around 4:00 in the morning and the satellite pix have shown almost no moisture since then. The National Weather Service forecast has been saying, since they updated it this morning at 10:55 AM…
Partly cloudy. A slight chance of showers through early afternoon. Highs in the mid 50s to lower 60s. Chance of rain 20 percent.
That's probably about as accurate as you could be. The Intellicast forecast was last updated at 1:00 PM and as I write this, it still says…
A steady rain this morning. Showers continuing this afternoon. High 58F. Winds W at 10 to 15 mph. Chance of rain 70%. Rainfall near a half an inch.
I don't know when they first posted that but it's been up (and been unchanged through updates) for 11 hours since the last raindrop fell. It's really a lovely afternoon out. Meanwhile, over at AccuWeather, they say, "Clouds and sun; a few showers," while www.weather.com (which is The Weather Channel) says rain for today, mostly cloudy tonight.
This is pretty much the way it always is. The National Weather Service is sometimes wrong because, well, weather forecasters are sometimes wrong. But the other online sources are either wrong (because no one's paying much attention to them) or they give such ambiguous prognostications that they're not wrong…they just aren't very useful. It amazes me the number of times it'll be pouring outside my window but one of these sites is still forecasting night and morning low clouds.
I think I once said here that if you want the best-possible weather forecast, you should go to all these sites and kind of mentally "average" what they say — like getting a second or third opinion from doctors. Lately though, I'm inclined to just head over to www.underground.com for the NWS forecasts. They're not always correct but at least they try.