The blacks usually come in first and then the grays and then the yellows. It's mostly based on soil temperature and that changes every year. Blacks pop above 45°F Grays closer to the 50° and above and the yellow seem consistent at closer to 60°. I usually probe the soil at a depth of 2"-3" and test in the morning and the evening to get a mean temp. They do pop earlier on southern facing slopes. I hope you find the mother load. I've been hunting morels for almost 20 years and I've never found more than a a couple pounds and never have found that elusive mother load. Hopefully this year will be different lol