I discovered a new NWS site that does my beloved ggweather.com site one better:

I found this site last week when ggweather wasn't receiving it's usual feed (it wasn't ggweather's fault). This site combines different parameters at different levels. For example, with ggweather, for relative humidity, you can only see that on the 700mb level. With this site, you can see it for the 850 and 500mb, so this gives me (and you) view into the lower level (850_rh_ht) and upper level moisture (500_rh_ht) to anticipate cirrus for example, and low level cloud cover, esp. post frontal with multiple fronts.