Estimates from weather radar suggest that there has between 60 to 75 mm of precipitation since midnight across the mountains of NW Scotland. The rain shadow effect has been in overdrive for much of the day here in Scotland and so accumulations further east have been mollified by the sheltering effect of the mountains further west. It’s been a very mild day across much of Scotland thanks to the same broad warm sector that’s brought all the orographic rainfall to the west.
The maximum totals in the yellow weather warning for heavy rain from the Met Office (06-00) may have been a little on the low side, as the warning remains in force till midnight, the area should have really been extended to cover the Northwest Highlands as well.
I reckon that over the highest tops the precipitation was falling as snow till around 11 UTC this morning looking at the SIESAWS observations on Cairngorm. I should imagine that rain since then will have been stripped a lot of the large amounts of snow that existed on ground above 2,000 feet.