I use the Autobrite foam lance, excellent bit of kit, mixes the foam very accurately.
In the winter i give the car a pre wash using G101. Leave G101 for a few minutes then jet wash off and all the heavy dirt will be gone

, then snow foam and whilst this is left to dwell, i agitate the snow around the bottom of the car (with mit0 where the dirt can be hard to remove, then jet wash off.
Job done

Kevo