Unless you were born under a rock, you know Seattle sees its fair share of rainy days. On average the city sees roughly 150 days of rain each year, which is more than any city east of the Rockies.
So when they break their single day rainfall record you take notice. The new record broke the previous by only .01″. The new record is 1.20″ of rain in a single day. If that precip were to fall as snow at 30°F, it would roughly amount to 1-2 feet of new snow (*depending on density).
The previous record of 1.19″ was set in 1958.
All this moisture is also set to impact the mountains where Mount Baker and Mount Rainier should both see over 10 FEET of new snow near their summits.
HYDROLOGIC OUTLOOK NATIONAL WEATHER SERVICE SEATTLE WA 328 PM PDT Wed Oct 18 2017
…Heavy rainfall will Give a Threat of Flooding to Many Western Washington Rivers Saturday night and Sunday…
A period of significant rainfall is forecast by weather prediction models from later Saturday through Sunday. This rainfall may produce minor flooding on area rivers starting Saturday night and continuing through Sunday or Sunday night.
While it is difficult at this time to pinpoint exactly where and when the heaviest rainfall and highest threat for flooding will occur, it appears that the greatest threat will be over the southern half of Western Washington Saturday night and Sunday.
Please continue to monitor latest forecasts since conditions can change.