Daily minimum temperatures less than the 15th percentile, or near freezing or sub-freezing temps. But I believe it's also up to some interpretation as is seen fit as well.
Juanita (Kirkland) has been totally dry all evening and freezing rain just started with zero lead up. Everything's been showing and saying snow or sleet for at least an hour before we were to switch over but the fact it just began suddenly feels like a bad sign.