Onion question

Are they Autumn or Spring planting variety.
If they're autumn planting, I'd start them in modules in a greenhouse, that's what I did last year, and done this year for my garlic. Under a cloche somewhere sheltered might work, at a pinch.
You might be asking for trouble planting any outside in the open, right now, with snow/low temperatures forecast for the next couple of weeks.

I stopped growing autumn sets this year because I found I had better results from overwintering onions from seed the Japanese variety Element for spring planting had good results  as for spring sowings  with both sets and seed the spring sowings did take a tad longer to produce but one of the variety we grew from seed santero was a good cropper as was the sets Turbo sets

 well snowboar as I said we grow Element [Japanese] and we don't plant out until spring when the ground warms up also a friend of ours who grows good veg including onions always starts his onion seed of around the end of March in a cat litter tray and plants out when the onion plants have got established and boy does he have good  onions as I said we both grow santero I'm also going to grow some other varieties [Kings] Bonus and a red onion Magnate  [Robinson's] mammoth  red [Browns] exhibition I think we should have enough onions to last us if they produce a decent crop 

That's exactly what i did last year.. I put them into pots with some multi purpose compost and kept them in the greenhouse house, then in the spring I just planted them out, all but 2 failed to grow!