This is another decent one that hasn't been mentioned, not real 'long range' per se, but a good aviation WX site nonetheless.

www.usairnet.com/weather/

Try this:

http://wxweb.meteostar.com/models/ipsm_looper.php?PROD=2010060500_WUS_NAM_SFC_SLP_THK_PRECIP_WINDS

This site has the NAM and GFS climate models. There are a few different models used by NOAA and NWS, etc. I've found NAM and GFS to both be good, but usually differ as time increases. You have to enter info in the pull down menus for it to work.

stewartb » Thu Dec 29, 2011 8:23 am
Weather forecast reliability varies by region. Alaska weath forecasts are unreliable. Nobody's fault, it's just the nature of the beast.

That fits here in Central and Northern Nevada. Especially the last couple of years. Lots of sunny/high cloud/light wind days when it was supposed to be precip/low cloud/winds.

I was told by some NOAA folks that they aren't allowed to use local knowledge anymore to change forecasts even when it makes sense to do so. I was told they now they look at the models and have to "pick" the one they believe will be the closest even when they know it is wrong. WTF?

One positive outcome is I've sure got a lot better at interpreting weather info and judging my own 24hr forecasts.

I generally try to watch the long-range forecast through a tall glass of whiskey.

I can't actually prove that this increases the accuracy of the forecasts, but I don't seem to mind as much about how wrong they always are.

I like the NWS "Hourly Weather Graph" that you can get after selecting a location from their main page. The link is in the bottom right of the page. You can also get the tabular version by clicking on one of the graph lines. It shows the hourly forecast for any day that you select up to a week ahead. You can select the products including ceiling height, visibility and thunder potential from the form at the top. Accuracy improves as you get closer to the flying day. Here's a link to one for Asheville NC:
http://forecast.weather.gov/MapClick.php?w0=t&w1=td&w2=wc&w3=sfcwind&w3u=1&w4=sky&w5=pop&w6=rh&w7=thunder&w8=rain&w9=snow&w10=fzg&w11=sleet&w15u=1&w16u=1&AheadHour=107&Submit=Submit&FcstType=graphical&textField1=35.57410&textField2=-82.54880&site=all&unit=0&dd=0&bw=0

NWS is the data source for all the others as someone mentioned. Their Graphical Forecast is pretty useful, too:
http://graphical.weather.gov/sectors/northcarolina.php#tabs