The Puget Sound region has been socked in by a strong ridge of high pressure which has resulted in clear skies but also two areas of concern weather forecasters have been monitoring, icy roads and air quality.
The National Weather Service issued a Special Statement this afternoon warning of the potential for frost and black ice on road and sidewalk surfaces again tonight and Thursday morning.
The statement said,
With temperatures dropping below freezing again tonight and Thursday morning, areas of frost and patchy black ice will create locally hazardous driving conditions across western Washington. The weather and road conditions tonight and Thursday morning will be similar to the conditions that contributed to numerous traffic accidents this morning. Temperatures vary widely over a short distance, so you can drive into an area of freezing temperatures and icy roads suddenly and without warning.
The traffic incidents referred to included a multivehicle crash on I-5 that closed the southbound lanes this morning just before the Nooksack River bridge. First responders reported the roadway in the area was coated in black ice. The sheen on the roadway is visible in the image above (WSDOT traffic camera).
This afternoon NWS forecasters reported air quality was showing some early signs of worsening, but still remained generally good due to a moderate northeast breeze. As the air flow becomes more easterly and weakens Thursday night and Friday, air stagnation will worsen and air quality could begin to deteriorate.
NWS forecasters have held off issuing an air stagnation advisory as they do this in coordination with local and state agencies. Air quality will be revisited daily while the dry stagnant weather continues.
Monitoring air quality in the Ferndale area has become more challenging since the nearest air quality monitoring station, located in Custer on Loomis Trail Road, has stopped reporting live real-time data since late October. According to Northwest Clean Air Agency (NWCAA) officials, the station is still collecting data and the equipment has been transferred to a brand new trailer. But the real-time reporting link to the Department of Ecology has stopped working. NWCAA and Ecology are working to resume real-time information reporting.
According to NWS forecasters, the strong upper ridge that has brought dry weather to Western Washington is expected to remain in place at least into next week. “The air mass is stable and should become increasingly stagnant Friday through the weekend,” say forecasters.