Rain showers are moving onto the coast now and move inland by late evening. There will be some rain continuing most of the night Thursday into Friday morning, with some breaks here and there. This rainfall will be light to moderate, but bring some nice wetting rains to the area to start Friday.
This will be the leading edge of an unusual “atmospheric river” bringing a stream of rich moisture across the Pacific right into Western Washington. This is a fairly common feature in our fall weather but happens this time of year perhaps one in a decade. The last time we had an inch or more in the first part of August in Seattle (through Aug. 16) was indeed ten years ago — in 2015.
And as compared to fall or winter atmospheric rivers which can cause all kinds of problems like flooding and landslides, this one will be almost entirely beneficial to the area. Soils are ready to gulp up water and low river levels mean water rises will be of little consequence.
Rain will increase in intensity from midday Friday through Friday night across the area. While the rainfall totals will be impressive — one half to more than one inch or a little more across the lowlands — it should be spread out enough to prevent any urban flooding.
In the mountains, one to three inches of rain will fall which is excellent news to help extinguish our local fires. There’s a slight potential for rainfall to cause flooding near burn scars, but most areas will just get benefit from this. Some west facing slopes could get even more than three inches from this event.
It will also be blustery on Friday with this weather system but no significant wind is expected. Highs will be only in the 60s Friday.
Rain will end and taper to spotty showers Saturday morning, with showers continuing to taper Saturday evening. We’ll be mainly dry and mild from Sunday through early next week.
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