I've noticed a large discrepancy in the weather forecasts on weather.com vs weather underground. In particular the predicted temperature.

I've noticed up to 10 degrees difference. That's a big swing if you're trying to plan around low temps this time of year.

Anyone have any insight into this?

Anyone know the most reliable weather site?

I prefer the National weather service website, you can pinpoint the exact valley or mountain top you are going to and get a pretty accurate description of the weather.

Weather.com seems to general for me in the past and is way off sometimes.

Any North American meteorologist is just sticking their finger in the wind and making a guess. They've gotten pretty good at guessing, but it's still a guess. From what I understand, being sandwiched between 2 oceans, a sizable gulf, several sizable mountain ranges, the great lakes, and a gazillion weather zones, makes north america one of the most difficult places to accurately predict weather. So I think out of that, you're going to have one source be good for some places, and the other good other places, and one source will nail it one day and the other another day. If concern for absolute cold is paramount, I'd look at both and take the most extreme of the two and plan for that.

I have found combining national weather service predictions that take into consideration elevation and then adjusting the predictions with real-time data from the California dept of water resources (for example tuolumne meadows ) has generally been within 10 degrees for the first two days of a trip. After that, well... I have seen some serious variation.

--Mark

Edited by verber on 12/04/2009 09:06:08 MST.

If I want to see a ten day forecast, I go to Weather.com. Otherwise, I use the National Weather Service.

Some notable things to pay attention to on the NWS website:

- use the pinpoint forecast by clicking on your location on the map on the right.

- read any special weather statements.

- read the Forecast Discussion. It's amongst the links on the lower right side of the page. This is where the weather geek stuff is! It's gold!

- look at the other links like, "Mountain top and Remote Weather" (if available), Zone Area Forecast



Also, there are more and more online, highly detailed, regional specific weather forecasting blogs. They're generally based around ski areas. Two that I pay attention to are tahoeweatherdiscussion.com and the Dweeb Report (http://izotz.com/dweebreport/)

For California, this is a great starting point.

http://www.castlephotographics.com/weather.htm

I generally just use WeatherBug on my smartphone, since I got back to the U.S. I can usually find a station in a nearby pass or whatever to get an idea, and use the elevation 3.5F/1000ft rule of thumb.

Weather is probably the most difficult thing to forecast. That and things like the lottery and the economy. Four years of college gives you much insight over how difficult it really is. Even with computer models, it is still imperfect. By the time one model run is over, it's already outdated.

Okay, enough of that. I use NWS, and I also like WUnderground, which seems to take the NWS info, and enhance it a bit. The only thing I like from Weather.com is their regional snowfall forecast maps. (What ever happened to Paul Kocin?)

For once, the government agency has something over the private sector.

NASA?

Oh yeah, them too. But remember, that those first astronauts were flying on tons of thrust, all built by the lowest bidder.