Depends on what you intend to grow :-) Typically one works backwards from the planting outside date but it does differ from crop to crop. Have you tried posting this at the Winter Sowing forum? I'd also recommend a copy of Solomon's Growing Vegetables West of the Cascades - he has an entire chapter devoted to this topic.

You're right on track for winter-sown mustard crops: broccoli, cauliflower, mustard, brussels sprouts, cabbage, kohlrabi, kale and chard. Also, spinach and lettuce grow well in our cool fall weather. The fall is the perfect time to plant shrubs and perennials. And now is the time to plant spring bulbs (sometimes called 'fall bulbs' - depends on whether you refer to them by the bloom time or planting time). Since you have the houses, you can start annual seeds earlier than people who don't have them. If you have a heat source in those houses, you can start tomato, pepepr and eggplant seeds in late January or early February. Even unheated hoophouses can extend the growing season for tomatoes, peppers and eggplants clear into November. There are even some tender herbs that can grow well in hoophouses, such as purple ruffles basil and pesto perpetuo basil.