What are some of the challenges and solutions involved in growing tomatoes in the Pacific Northwest?
Growing tomatoes in the Pacific Northwest is very possible, but can present a number of challenges. The three biggest concerns revolve around:

1. A short growing season
2. Cooler summers
3. Wetter than average summers

Here are some solutions you can use to mitigate these challenges.

Do deal with the short growing season, you need to get a headstart on growing by using starters. What this means is that instead of planting a seed in the ground in Springtime, you start a seed indoors in late winter, grow it into a small to medium plant, then transplant that "starter", into the ground when the temperature is warm enough. You can buy starters from Nurseries, or start your own at home. Nursery starters are easier, but by growing at home you can experiment with more rare varieties and gain experience in cultivating a plant from the seedling stage. If you grow your own it's important to slowly climatize the plant to outdoor weather leading up to the transplant date by moving it outside starting with a couple hours a day, increasing an hour or two per day over 2-3 weeks. By using starters you essentially extend the growing season by giving your plant a multi month head start. 

Tomatoes mature best in warm to hot climates. The pacific northwest has cooler summers than many of the growing regions in the world. There is not a lot we can do to control mother nature, but there are one or two methods to help yourself here. Certain varieties of tomatoes do better in cooler summers - try and select these. If you're using starts from a local nursery they can guide you - starts from big national box stores might not be the best for your local Northwest climate. Another technique, if you are experiencing a cooler than normal Spring and start of Summer, is to build a "hoop house", using PVC pipe frame and a visqueen tarp. This will let light in and act as a mini-greenhouse, trapping heat around the plant. Keep in mind tomatoes need pollinators like bees to produce fruit, so once the plan t begins to flower you'll want to ensure pollination can occur.

Moisture creates issues with Tomato plants as they are very susceptible to various types of fungus that grow on the leaves. Blight is one in particular common among tomatoes. The wet summers we sometimes have create conditions on the leaves conducive to fungal growth, they can also splash fungus onto the leaves from the soil. The easiest way to deal with these two issues is in proper pruning. As early as you can prune any lower sets of leaves that could possibly come into contact with the ground. Don't do this too soon as the plant needs some leaves to grow. There are many ways to prune a tomato that you can read about, but one common one in wet areas is called single stemming - in this technique you prune "suckers", which are the small offshoots that grow in between the main stem and the leaf stems. By pruning the suckers you prevent too much bushy growth, which will help the leaves dry out with airflow after a rain storm. The last issue related to water is that heavy late season rains will cause the fruits to swell with water and crack. There's not an easy solution here. If it's towards the end of the season and a rainstorm is coming in, this can be a good time to pick all your fruit, your green tomatoes can be used for green salsas. Some will resort to building a tarp structure above the plants to stop the rain, though this can require a bit more work and ingenuity, and you'll need another system to keep the plants watered.

Overall, growing tomatoes in the Pacific Northwest is totally possible and very rewarding. Hopefully these tips help you to have a fruitful growing season!