I must agree with HvH on his one. That rain in the pic with the Tiger looks great, but nothing else is moving.  I treat my Dio's as a 3-D photo, thats why i don't use a clear plastic disk to show moving propellers on plans. I think it just looks silly.  I havn'et tried a scene in the rain yet, but its somthing i will have to try at some point.

Frankly, anything moving in a static scene looks ridiculous, IMHO... A diorama is a 3-D "snap-shot" of a moment... Falling rain, snow, moving smoke, winking muzzles flashes, etc, all look silly...

That said, I like to do "wet" dios where the rain is suggested by the appearance of the objects in it.. One of the better effects, I think, is to depict it as just having started to fall... I depict this be showing only the upper surfaces of objects as being "wet", be it the tops of AFVs with some wet streaking,, the helmets and shoulders/feet of figures, roads & streets just starting to be completely wet, but with dry areas under overhanging objects...

For static rain, you may use some materials as proposed above like clear sprues, fishing lines, etc. But for dynamic, falling rain you'll need Java applets. I've been using it for 10 years now. The only problem is that you can't show it on other sites rather than your own. This page shows what I'm talking about at the top of page:

http://www.falconbbs.com/model53a.htm

 remember seeing something like that in FSM (reader's gallery?) a few years ago (2000-2004'ish). The model was a diorama of an F1 racer on a wet track.

Maybe somebody else are able to dig up the exact reference.

DoC   

I remember this feature. The model was inside a Plexiglas box and the inside of the plexi had been grained with fine sandpaper to make it look like rain was falling. There was a lot more about water plumes from the wheels etc.

I was thinking the same thing.  Remember those "rain lamps" back in the 70's and early 80's?  I mean, it would look pretty fake just having fishing line strung in front of a diorama but perhaps in a shadow box could look pretty cool.

Some great advice here. If I might add:

1). Puddles of course.

2). Anything like vehicles, helmets, etc paint with a gloss varnish to give a shiney 'wet' look.

3). Uniforms if soaked would be darker than normal. If a light shower you could even go with painting the shoulders and upper parts a darker shade than arenas like the lower and inner parts of the sleeves that wouldn't get hit with rain.

The nice thing about modeling is it you don't like the look you can always paint over it. So experiment- you've nothing to lose!

Dr. Coffee

I remember seeing something like that in FSM (reader's gallery?) a few years ago (2000-2004'ish). The model was a diorama of an F1 racer on a wet track.

Maybe somebody else are able to dig up the exact reference.

DoC   

I think they had a piece of plexi glass that was streaked (to look through) and then made some "rooster tails" coming off the wheels.  I thought about building a dio then spraying future on it.  you wouldn't see the "rain" but I think you could pull off a scene where it looks "wet and rainy". 

Grizz

101stAirborne

I think it would be really cool if someone could pull off a diorama where it was raining...I don't know how it would be done. Possibly a shadow box?...

Have at it.

Well, you can certainly make a diorama look like its raining by an effect on the ground, and splashes are possible, but rain drops itself, nope, not without being fake.

A force perspective diorama, with the effects of the rain hitting the ground. Don't forget since you are doing a model, you must take in consideration of scale effect. Though rain drops vary in size, if you took a full drop and used it in a scale diorama, it would be like dumping pails of water instead of drops.

The drizzle effect in a forced perspective diorama can be achieve by using a diffused window pane to create a certain amount of distortion.

I'd go for the effect of water hitting puddles, give everything a wet looking sheen to it and position the figures as if they were protecting themselves from the rain. You could add a little dripping water from objects using Future I would imagine.

drops of Future on clear fishing line?

I actually know how to do this with stretched clear sprue...

101stAirborne

I think it would be really cool if someone could pull off a diorama where it was raining. I don't know if it has been done before and I don't know how it would be done. Possibly a shadow box?

I remember seeing something like that in FSM (reader's gallery?) a few years ago (2000-2004'ish). The model was a diorama of an F1 racer on a wet track.

Maybe somebody else are able to dig up the exact reference.

DoC   

Nah, a water can hung over the dio...when you want to show the effect: tilt for desired intensity...