Weather condition simulator product recommendation?

Hi. I'm looking for a product recommendation about weather condition
simulation w/image generation output -- something capable of
non-realtime image generation (~2-3 minutes of scene simulation/hour of
execution is fine). I need a product capable of rendering falling rain
fall (mm/hr), hail, haze, fog, lightening -- not so critical, snow
(mm/hr), sunshine, etc.

I need the capability to edit a patch of terrain to introduce things
like trees or rocks. Any ideas about what's inexpensive and works ok on
a Windows box? I don't like Billyware -- I'm an old UNIX guy myself,
but the budget is mighty tight. Thx.
--rick

.