I did this in 2000 (but with an old CAA PPL - not sure what has changed under JAR) and the FAA ticket required 3 hours of (dual) night flying which I seem to remember was optional, although your licence would be restricted. In addition their qualifying cross country needed to be slightly longer than the one I did under the CAA and their definition of "cross country" was different - I had loads of cross country time during my PPL but they wouldn't recognise cross country time where I hadn't landed away. Also cross country as far as I'm aware under JAR is a land away at a point up to 3nm from departure (or so the CAA told me at the time) - in the US it was 20nm.
Basically all your training is valid, subject to definitions like this being the same.
The skills test is similar (although just one trip like a checkout) and the written is fairly easy if a little different given air law and wx service differences etc.
I would double check all this in case anything has changed (it may well have) but it will give you a pointer to the areas you need to look into. If you can get hold of a copy of FAR-AIM it will spell out the details.
Wx question - I'm going back out in June and have been told it is going to be "hot and clear"!
http://www.cityrating.com/ will give you weather histories.
Note that schools on the coast (Oakland, San Diego etc.) suffer from a marine layer and can be IFR when places inland are basking in sunshine.
Hufty