When the soil can be worked is tilling time. That means the ground is unfrozen and dried out enough to be crumbly, not clumpy. If you squeeze some in your hand it should form a loose ball, that falls apart easily. If it forms a tight, solid ball, it is too wet. If you till when wet, it will clump up and stay clumped all season!
If you still have a foot of snow, probably your forsythias aren't blooming yet either! Do you even have forsythia that far north?