Rain Sunday Will Be 'Unusual', Forecasts Indicate

SEATTLE, WA - Get ready for - yes - another very wet weekend. Forecasters are warning of an "unusual heavy rain event" coming Sunday, and increased risk of landslides due to saturated soil across Western Washington.

Sunday's rain event is "unusual," University of Washington meteorologist Cliff Mass explained, because the rain is coming from a different direction than usual.

So you may ask...so who cares about the direction of the moisture? It turns out it does make a difference, because the winds bringing in the moisture will be different. Instead of the normal southerly or southwesterly flow, there will be westerly (from the west) flow.

This is important. The Cascades are roughly a north-south barrier and upslope flow, and resulting precipitation, can be greater for westerly than southerly flow. In the business we call this more orographic enhancement.

The NWS, meanwhile, has issued a special weather statement warning of a "marginal" landslide threat, especially for coastal hillsides.

Here's a look at the weekend forecast:

Friday Night: Rain likely, mainly after 11pm. Cloudy, with a low around 46. South southwest wind 10 to 16 mph, with gusts as high as 21 mph. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch possible.

Saturday: A 50 percent chance of rain. Cloudy, with a high near 51. South wind 7 to 13 mph.

Saturday Night: Rain likely. Cloudy, with a low around 47. South southwest wind 5 to 8 mph. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch possible.

Sunday: Rain. High near 53. Breezy, with a south southwest wind 16 to 23 mph, with gusts as high as 30 mph. Chance of precipitation is 80%. New precipitation amounts between a quarter and half of an inch possible.

Sunday Night: Rain likely, mainly before 11pm. Mostly cloudy, with a low around 46. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch possible.

Image courtesy National Weather Service