I've been waiting for temps consistently over 50. It seems we have reached that. Don't have a soil thermometer. Can I plant them outside now that we had those 80 degree days over the weekend?
Soil temperature is more important than air temperature, because the roots (which sustain the plant) are in the soil. The Oregon State University’s Hyslop Weather Station tracks soil temperature throughout the year. Though it is a few miles south of us, it gives an excellent picture of what’s going on.
You will see that their soil temperature at four inches is hovering above the high 50s—not unreasonable for tomato starts.
That said, some of the answer to your question depends on your soil conditions. Clay soil warms up slower than a raised bed. North-facing slopes warm up later than south-facing ones.
For more perspective, there are a number of folks tracking soil temperature in our area. Searching on the phrase “soil temperature Portland” gets a few reliable sites.
If you do decide to put your starts out now, be sure to give them adequate water or some shade.