I checked weather again, Friday in NY changed from "shower" to "Cloudy", so hope it stays this way, really hope Delta won't cancel the flight to Seattle!
I don't think they cancel flights for rain anyway - thunderstorms maybe but not just rain. If so, there would be hardly any flights into Seattle at all

I would not worry.
Delta cancels flight in case of storm before – one storm night we received friend’s call that their flight from texas to Ukraine with connection at JFK cancelled cos of storm. They stuck at JFK and Delta told customers since cancellation of flight because of weather, not delta’s fault, Delta doesn’t even provide hotel accommodations for them. They had to stay at our living room to save hotel money and get up 5am to catch next flight to Ukraine.
If only rain, I wouldn’t worry, but weather site says “storm”…