To start, I used masking tape over the horizon and applied a wash from Burnt Umber & Viridian Green up to Prussian Blue, for distant woodland and sky. Added pale tree trunks ‘behind’ the horizon after the sky was dry; before removing the tape. Then added shadows in the snow, mixing Prussian and Ultramarine Blues.
After a bit more patient drying.. throw on some random trees and shadows. We’re done.