There are undoubtedly other internet sites of interest, but these will get you started. Some plants will not flower until after they have been exposed to cold temperatures. This exposure to cold temperatures, resulting in physiological changes in the plant, is called vernalization. Not all plans have a vernalization requirement, and the degree of vernalization required can vary within a species. Contrary to popular belief, the best vernalization temperatures are in the 40 F - 50 F range, not at colder temperatures.
Winter wheat does have a vernalization requirement.
Most spring wheats do not, or have very low vernalization requirements. The table below groups varieties with low, intermediate, and high vernalization requirements. Cultivars with a higher vernalization requirement need more exposure to cold temperatures. Most of the current varieties commonly grown in Oregon have intermediate vernalization requirements. Assuming satisfactory field conditions, you can safely plant any winter wheat before January 1 in all regions of Oregon with minimal risk.