Creating email alert when an item goes on back order

Ok, so what if I want to send an email alert when an Item goes from in stock to backorder? For instance, customer places an order on an item that is already in backorder status, I don't want an email alert for that.

However, if an Item goes from in stock then to a backorder status I want an email alert then since it is possible to have an item out of stock but not in backorder status. 

To be more specific, if backorder value goes from 0 to some positive integer then I want an email alert, however, I don't want one if the backorder value goes from 1 to 11 or the like. Hope I made sense.  The issue I'm running into is that the Item fields that I could use in a simple formula are not available in the updated fields option for emails.