If you have someplace you can keep it dry, it should be just fine for spring. If it is wet and stored outdoors in your climate you might have to thaw it out due to it being one solid frozen lump.

Hi Claubill
I would recommend that you buy the bails of pro mix  its great for starting seeds and cuttings indoors. Plus its cheaper than picking up many bags of soil. The problem with getting it too early is in fact that it will get wet and possibly harbour pests, fungus etc. Just like it would with soil. Many people sterilize their soil prior to using it to start seeds. If you check out the seed starting forum someone should be able to tell you how to do this. I do believe they bake the soil in the oven or microwave it prior to using it. If you use it for winter sowing then it should be o.k. I will be coming up to Sudbury in the fall and could either help you pick it up with my truck if you want to wait a bit.
Let me know.

Laura