There's an Air Stagnation Advisory for western Chelan and Okanogan counties until 11pm. 

National Weather Service Meteorologist Steven Van Horn says warmer air above is keeping colder air near the ground surface locked in with little movement upward. 

 “Air near the surface is staying near the surface, so any pollutants that are being released into the atmosphere at the surface are staying near the surface,” said Van Horn. “So, you have pollutants more likely to build up because of that. 

The stagnant air is especially locked in at locations such as Wenatchee, which sit next to the mountains. 

“The mountains and the topography, those play a big role in that because if your mixing heights are lower, then the air in the valleys, especially the deeper valleys down from the mountains has an even harder time of mixing,” Van Horn said.   

The Air Stagnation Advisory is also affecting parts of eastern Washington, including Spokane. 

The dirty air could clear out quickly, though, as there's a 100 percent chance of rain Wednesday night. The rain chance continues on Thursday before the sun is forecast to reappear Friday. There'll be off and on chances of rain over the upcoming weekend.

Daytime highs will remain slightly above normal in the low and mid 50's through Tuesday. Friday will be the warmest day of the week at 57.

It's an El Nino year, which means weather is forecast to be warmer and drier than normal in the Pacific Northwest.

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