Zeke,
I fly in Australia, so I don't get the opportunity to point my radar at snow fields, however you are not quite correct in saying that weather radar will not detect snow covered terrain. The Bendix corporation says that rock covered with ice and snow (particularly powdered snow) can be unreliable, but previous crew on the ANZ Mt. Erebus flights had reported that radar terrain contours matched closely with the actual terrain.
Weather radar will not detect dry snow in the air (correct) but it is not a "water detector" in the sense that it always detects water. Radar will not detect bodies of water on the ground (lakes, rivers etc) as the beam is reflected from the flat surface away from the aircraft. Terrain is detected as is scatters the beam, and the back scatter can be seen on the display - I would think that snow covered terrain would react the same way.
The fact that weather radar in transport jets is pitch stabilised is what makes it a good terrain awareness (note, not avoidance) device. Most jets descend on an angle of about 4° to the terrain, so setting your radar with the bottom of the beam at 4° nose down (and it will maintain this on descent as it is stabilised) will show anything in the way of your descent on the way down - terrain or weather.
It is not known whether the Mt. Erebus crew used their radar for terrain mapping during the accident flight - certainly nothing on the CVR mentions it. As they were flying "visually" at the time it is doubtful that they would have been referencing it in any case.
[This message has been edited by Checkboard (edited 02 June 2001).]