Chilly & Showery, Upcoming Atmospheric River

FastCast—Monday, Apr. 3 to Friday, Apr. 7:

A mixed bag of weather is ahead this week in Western Washington. Expect residual showers to continue on Monday, especially in the morning and evening. Some showers will carry into Tuesday morning. Then, expect a partly to mostly sunny Tuesday afternoon. Wednesday will be mostly cloudy across the region, with rain spreading inland from the coast in the evening. An atmospheric river will impact the area from late Wednesday through Thursday, likely bringing 1-2” of rain for the lowlands and 2-4” on the coast (more details in the coming days). Expect the atmospheric river to move out of the area by midday Friday. In the mountains, expect 2-4” of snow at the passes through Tuesday. Snow levels in the atmospheric river will start out around 2,500 feet on Wednesday night, but will steadily increase to 5,500 feet by Friday. In the lowlands, expect this week’s highs to be in the low 50s, except the mid 50s on Friday. Lows will increase from the mid 30s to mid 40s through the week. Some isolated areas may drop below freezing in the mornings during the first half of the week.

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Continue reading the full blog below!

After a showery weekend, with small hail, brief snow (in isolated spots), and even a few thunderstorms, showers will taper off through Tuesday. Generally, expect 0.1-0.4” of rain in showers across the lowlands & coast through Tuesday.

Temperatures will be chilly to start the week, as seen in the European model’s forecast for Monday’s highs.

Expect highs in the lowlands and on the coast to be in the upper 40s to low 50s, a trend that will continue through most of the week. In Eastern Washington, highs will be in the low to mid 40s, except in the low to mid 50s in the Lower Columbia Basin.

Low temperatures will be on the cold side early this week, shown in the European model’s forecast for Wednesday morning’s lows.

Similar lows are expected on Monday morning as well. Expect lows in the low to mid 30s, warmest near the water. Some outlying areas may drop into the upper 20s. Eastern Washington will be quite cold, with lows in the low 20s near the Cascades, and in the mid 20s to low 30s elsewhere.

Now for the real action…the atmospheric river expected to impact the region from Wednesday night through midday Friday. The atmospheric river is seen below on the UW model.

As of now, the SW to NE orientation of this atmospheric river ensures that the Seattle area likely won’t be rainshadowed. 

What kind of rainfall amounts could we be looking at? Let’s take a look at the European model’s forecast below, showing total rain through next Saturday.

(Keep in mind, this forecast does include rain that will fall from Sunday to Tuesday). With that noted, we can reasonably expect 1-2” of rain in the lowlands from late Wednesday to midday Friday, except 0.4-1” from Oak Harbor to the Canadian border, due to a rain shadow. The coast will likely pick up 2-4”, and Eastern Washington will get 0.5-1.4”. The Willamette Valley and SW WA could get up to 2.5” as well.

With snow levels expected to rise to near 5,500 feet, mountain precipitation isn’t certain yet. Be sure to stay tuned to the blog for more updates on the atmospheric river!

Let’s end with some great news! The outlook below from the NWS Climate Prediction Center shows temperature probabilities from April 8-12.

This is a huge improvement from the consistent below average temperatures we have been experiencing! Across WA, there is a 40-80% probability of above average temperatures! 

What does this mean for the lowlands? Let’s just say that mid 60s are likely, and 70s aren’t out of the question! Stay tuned…details are still coming into focus!