That's very weird looking... Perhaps sfc based showers drifting towards the low center offshore? But the straight banding is confusing. It looks like a real artifact, and I don't recall seeing anything like that on the models leading up to today.
It’s a good thing it was created, the damage done to the environment before water treatment was implemented is sad to think about. We pull out all sediments, heavy metals and petroleum out of the water. Before this job all my previous jobs felt meaningless but the impact of what we do is measurable and important.
Speaking of the possibilities in the current climate we have. Even with the warming we've had in the past 70 years or so January 1950 would still end averaging well below 30 degrees for SEA. Jan 1862 averaged around 21 at Fort Vancouver and 22 and Fort Steilacoom so those would still equate to like 26 or so now.