I'm looking for some resource that tells me typical weather conditions, and other information, when planning a trip. Ideally it would be something like - "prone to flooding in winter", or "often closed by snow". The kind of information you'd hope to get from a ranger, or state visitors center, but for research. I'm planning a trip that will take me through desert and mountain, and want to make some intelligent choices up front, and then back them up with whatever local resources I can find.

For example, my boss recalled a time driving through Albequerque, NM, that had horrendous flooding on the freeway - and the detour through town revealed manhole covers blasted off by flood water, from underneath. Valuable, first hand experience.

Can't find anything online to flesh this out though!

FIRST-Thank you Nighthiker for that web site!
SECOND-I am an Intel gathering/disseminator fool. I have a 5 drawer file cabinet full of info gathered from states, countries, pertinent news articles, etc. (it even includes a Dublin phone book). When planning a trip, I pull all of the pertinent files and start going over them.
THIRD-as a former aerial observer, navigator, and current towboat Captain, I keep charts and maps and make notes on them (local info). Notes include highwater currents, fishing spots, fords and dry creeks that are dangerous after light, medium, or heavy rains, etc.
FOURTH-I hang onto every copy of the Mother Earth News and National Geographics (including CD's) for further info.

This is how I keep local info that can save my butt !

I do a lot of googling to find out information on road conditions. For example, you do a search for "state of california." When you get to that site you look over their home page for something about highway department or road information. You will usually find something like this . On that page you just enter the hwy number you are interested in, and it will tell you about it. Every state I have tried has some form of website, but of course they all work differently.

Some counties in some states have similar sites, some don't. If you are interested in something like a national park, you can google up their website and often find road info.

Even if you don't find road info on a website, you can always find a phone number to call and ask...

In most states, you can call the highway patrol or state trooper (not 9-1-1) and they can tell you the weather conditions. Some even have hotlines. As stated earlier, most states have conditions online plus traffic cam access.

I have found that if you google "your state" DOT (department of transportation) that most of them have current road conditions and a information phone number. Like in Wyoming, Type WYDOT or NEDOT (for Nebraska) and you will have more information then you can possible want. I use this almost every trip I take as the weather on one side of the state can be 70 degrees and snowing on the other side.