I've had alfalfa in a blend of clover-type seeds that I've successfully frost seeded a number of times. Trouble with alfalfa isn't that it can't be frost seeded, but more that a stand of it is hard to maintain by simply mowing, like clover. The reason I've added it to seed blends, is for better drought resistance. BUT, it needs to establish itself before it'll be very resistant to drought. Unless you have confidence that you can get it seeded and now have a significant drought year, I'd say just skip it and go with a mixed red/white clover blend.....either by frost seeding or by seeding later in Spring along with a nurse crop like spring oats.