Last Frost Date

Always on my mind - when do I get to plant things? For Denver, looks like with an 80% confidence the last frost date is May 12 and with 90% confidence, it's May 18. Not being a gambler, I think I'll stick to the latter date. I have now calculated the weeks back and find that today I get to sprout my tomatoes!! And then I realize I'm leaving town for a week in April, and can seedlings really live for one week waterless? What to do?? As I agonize over my Excel chart of planting dates, I'm thinking the only solution is to wait and, once sprouted, stick them under a grow light and hope for the best. . .