I wash mine weekly during the winter. Granted, it doesn't get nearly as cold down here but even when it is in the 20's I'll get out there and clean her up. The main thing it bundling up really good and wearing waterproof boots. The other main thing I have is this lined mit.
http://www.griotsgarage.com/catalog.jsp?&SKU=10259 Your hand will never get cold with this. Of course it alos help to be able to pull it in a heated garage for drying.