Originally posted by Ole One generally must overexpose one to two stops for snow to be rendered white.
Per that rule your RAW images ought to be underexposed as well as the JPGs. That the RAW images are differently exposed than the JPGs is a bit baffling.
I agree and the OPs later post shows exactly this
Originally posted by MSL I believe that is the source of your problem. If the camera thinks it is a cloudy day, it is expecting average, diffuse lighting, and thus that the average of your background should be close to the 18% grey. But your background is mostly white. I don't know if you have a copy of the Pentax DCU (came with my K-5) but that will let you reprocess the images as if you were using the camera settings. I bet if you used a different white balance; and one that by default brightened images, they would all come out looking okay.
this is wrong. The WB does not make assumptions about direct vs diffuse light only on the color temperature. The camera exposed correctly for metering white snow. It is important to remember the camera will try to meter for a "middle grey" solution, which is what the op got.
In fact this is nothing to do with raw vs joeg, it is all to do with understanding the camera and metering.