So now your leeks are looking pretty good, the weather is back to spring. It is time to harden off the seedlings. The process of hardening off a seedling is where you put them outside in a controlled environment like a cold frame so that the seedlings can gradually acclimate to an outdoor lifestyle. I would have done this about a week ago but Mother Nature did not cooperate with the 25 degrees and 20 mph winds.
So outside they go. 
They are simply going on a table in my backyard as the weather projection is for moderate temperatures and little wind/rain. They have been awhile since they have had a haircut and they are looking pretty shaggy, so after a quick trim, they will stay outside for the next few days with a sunday or monday planting target.
Keep track of water needs as they can dry out in sun and wind faster than in your basement and make sure you continue to bottom water with a dilute water soluble complete fertilizer until planting time.