SEA might be ILS CATIII (don't know where to check, I guess www.faa.gov). AS has really fancy ILS equipment on many of their planes due to Alaskan weather, and I think SEA upgraded to work with it, as well, cause when the weather is really atrocious, my AS flights always get in and out. ^

Once coming in on the morning 777 from ORD it was noted that SEA was under heavy fog (it actually covered only the southern half of the runway and airport, with the northern half open) and the pilot noted over the PA that the weather was bad, so we might have to wait a bit, but the plane and crew were certified to land in those conditions.