Plant closing and notice period questions (update)

My employer announced that the site will close and gave us written notice. Thank you in advance. I do not know if I should start looking now or wait for severance news. Should I stay for the bonus?

Start your search early. I wish I had begun the day of the notice.

Thanks for writing this out. I went through something close to it 3 months ago, and it got easier once I kept a simple log of every call and form.