By our calculations, you should look at sowing Italian Red of Florence about 28 days before your last frost date.
hard-to-find Italian heirloom.
Rossa Lunga di Firenze, Rossa di Firenze
Rossa Lunga di Firenza, Rossa di Firenza, Long Red of Florence, Rouge Longue de Florence, Rouge de Florence
1 http://www.cherrygal.com/onionlongredflorenceheirloomseeds2010-p-5051.html