My concern would be that critters get the seeds or that they wash away when the snow melts and the ground heaves.

You know your garden best, so you decide.

What you've done is called direct sowing. There are two major issues: One that bakemon has already mentioned that the seeds may get washed away before they can germinate. The other is that with direct sowing if the soil was not well prepared, the seeds may not have made good contact and so may have dried out or otherwise not stay viable. Soil preparation includes roughing up the surface to provide cracks and valleys for the seeds to fall into and removing leaf or mulch cover so the seeds make it to the soil. Then the question is how much leaf cover will you need to remove come spring without disturbing your seeds? With the drying out question, how long before snowfall did you direct sow the seeds and did you have a period where the soil dried out? (Preventing drying out without having to water everyy day or so is why winter sowing uses sealed containers (with vent holes to prevent overly wet conditions and rooted seeds.)

My feeling is that the work of soil prep for direct sowing and the amount of failure to germinate is enough that the work of wintersowing, which can be done little by little through the long winter evenings, is more wothwhile, especially for vegetables.

You should visit the dollar and discount stores and bring a few bucks to buy some seeds.

Seeds are food, you just fed mother nature's critters and crawlers--you may see some seedlings, but they'll be few and mixed in with weed seedlings too.

Next year, save yourself the double labor and do Winter Sow instead of direct sowing.

If you didn't want to keep the seeds anyway and you wanted to try it, why not? All you are out is a few seeds and all you've gained is some knowledge. I live in a zone 4 too and I'd be surprised if the veggies come up, but I'd also be delighted. Snow can act as a good protection against bitter wind and critters, especially if it has stayed put. I have never winter sowed before and am just now reading about it and decided to do an experiment of my own. I put different seeds (many veggies) in various containers and set them in my greenhouse in the same manner as others set them outside. I also sowed a couple of ground beds with different things and covered them with a plastic cover on cold nights, and remove it when it is fairly warm (50 or so in the greenhouse). I am keeping them moist though not enough to rot. I am interested to see what varieties, if any, will come up. I figure the best way to find out something is to try it. With that in mind I am trying several varieties of tomatoes, cauliflower, lettuce, spinach, peas, carrots, onions, strawberries, chives, rhubarb, tarragon, violas, black-eyed susan. I too am anxious to see. I will start some other things like I usually do - indoors or later in the greenhouse. This early stuff is the experiement and I too look forward to seeing the results.

Let us know how it turns out.