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Oregon State Smoke Forecast for Thursday and Friday

Oregon State Smoke Forecast for Thursday- Friday September 7-8, 2017
Issued:  Wednesday September 6, 2017
Forecaster.  R. Graw, USDA Forest Service

A change is in store for the state on Thursday and Friday.  A low pressure system off the coast will bring a change in wind direction, cooler temperatures, precipitation, and even some lightning. Rain will begin tonight in the very southwest corner of the state, over the Chetco Bar Fire, but less than 1/10 of an inch is expected.   Tomorrow, rain will move over the southern Cascades, whereas as much as 1/2” could fall in some locations, as shown in Figure 1 below taken from the University of Washington Weather Research Model, 1.33 km domain.  However, there is some uncertainty in this prediction due to the unknown nature of how the smoke will interact with these storms.  If indeed, the forecast holds to accurate, this could help reduce fire activity and smoke.

Figure 1.  24-hour total precipitation expected for the period ending at 5 pm on Thursday September 7, 2017.

Overnight mixing will be poor on Wednesday night leading to night-time drainage flows of smoke moving from the fires down and along river valleys.  This has been seen in several locations including  the Chetco River near Brookings, the McKenzie River near OakRidge and Eugene, and Trout, Pole, and Whychus Creek near Sisters.   However, vertical mixing is expected to be excellent across the state on Thursday allowing surface smoke to mix upwards and out after the morning inversion breaks, but also allows smoke aloft to mix down to the surface.  

Figure 2 illustrate the overall smoke pattern expected for tomorrow afternoon at 1 pm, and fairly representative of conditions throughout the day.   The figure is from the High Resolution Rapid Refresh (HRRR) smoke model.  SBy tomorrow morning, clearing is expected over the Oregon coast.  The Willamette Valley will see significant improvement in air quality compared with the last two days, but perhaps not total clearing.   Southwestern Oregon, will see much improvement as the rains will help decrease fire activity and scrub out much of the smoke in the atmosphere.  However, light to moderate smoke will still be present in the Rogue Valley with higher concentrations of smoke in Cave Junction.  Conditions should also improve over the Cascades as well, but could be unhealthy in areas close to the fires.  Central Oregon north to the Washington Board including Bend, Prineville, Madras, Hood River, the Dalles, Hermiston and Pendleton will see much higher concentrations of smoke with the return of westerly winds.   Eastern Oregon from Burns north will likely also see relatively high concentrations of smoke.   Conditions will improve for many parts of central and eastern Oregon throughout the day as mixing of surface level smoke occurs.  However, the Blue Mountains including LaGrande will likely not get much relief tomorrow.

Figure 2.  Model-predicted Smoke and Wind Pattern for 1pm on Thursday September 7, 2017

Friday:  September 8, 2017

The rain will continue on Friday covering an ares from the Rogue Valley northeastward to Madras, and even some rain in the Columbia River Gorge.   Some areas may see up to an inch of rain, as indicated by the medium-green areas in Figure 3. 

Figure 3.  24-hour total precipitation expected for the period ending at 5 pm on Friday, September 8, 2017

Friday will start out with northwest winds over western Oregon which will keep the air quality in good condition for the coast and Willamette Valley.  This will also help keep the Rogue Valley in relatively good air quality as well, particularly if the Horse Prairie fire has diminished fire activity and smoke production from the rains.  West winds will prevail in the Columbia River Gorge, but because of the expected rain, fire activity and smoke production will be tempered.  Nonetheless the residual smoke from smoldering fuels will be transported into Hood River and The Dalles.  Central and Eastern Oregon will experience westerly winds as well, except south-central and southeast Oregon where southerly winds will occur.  This will help keep Klamath Falls and Lakeview in relatively good air quality.  Central Oregon will likely also experience much improved air quality, unless the rains aren’t realized.  All in all, this looks like good news for much of the state.   However, its very dependent upon the rains.

As always, please refer to the Air Resource Advisor Reports for more detailed forecasts associated with individual fires. 

Disclaimer:  Weather and fire activity can change quickly.  Please check back for updates to these forecasts as conditions change.