Previsão do tempo, weather forecast: Finally.... Smoke Relief for the Northwest

Saturday, September 19, 2020

Finally.... Smoke Relief for the Northwest

As the models have been signaling for days, air quality over western Oregon and Washington has improved dramatically over the past 24 h, with much of the region enjoying relatively clean air (green colors on the map below). Clean air is surging over the Cascades and should soon displace the smoky air over the NW side of WA and northern Idaho.

As shown by the plot at Seattle, the rapid decline in particulate levels started Friday evening, with plummeting values overnight as western winds (winds from the west) strengthened.

The improvement in air quality is the result of a significant change in circulation, with high pressure to the southwest and modest westerly/northwesterly flow pushing clean Pacific air into the region. The forecast map for the flow at approximately 3000 ft valid at 5 PM today, shows the story.

There is some residual smoke out there (see satellite image from yesterday) that will move inland during the next few days: but not enough to push us into unhealthy levels. The smoke is that hazy area over the SW side of the image.

The disturbance that led the transition to our clean air brought the first real rain in a long time to our region (see 24h totals ending 8 AM Saturday below), with a number of locations getting a quarter to a half inch. We acutely needed the precipitation.

One issue of concern is that there were a number of thunderstorms embedded in the showers, with copious lightning over the Cascades and western Oregon. Lightning that could initiate new fires.

The latest HRRR-SMOKE forecasts (below) project improving conditions at 2 PM today, with serious smoke limited to NE Washington, Montana, and California.

By Sunday at 4 PM, even Idaho and Montana are clear. But the remaining fires in both Oregon and California continue to produce serious smoke for those downwind.