Forecast Issued: Friday September 15, 2017
Forecaster: R. Graw, USDA Forest Service
A low pressure system approaching the state will bring east winds on Saturday and southwesterly winds and rain on Sunday. This will be followed by a series of bands that will continue to bring precipitation throughout next week. These events will be a significant slowing event for the fires. In fact, we may even see snow above 5000 feet in elevation next week. While this is good news, we have one more day of a smoke for the west side of the state.
Saturday: September 16, 2017
The approaching low pressure system will bring the return of east winds over the fires, bringing smoke into areas east of the fires across the state. Figure 1 illustrates the spatial pattern and relative concentrations of smoke for Saturday. On the west side of the state, the Willamette Valley, Roseburg, and the Rogue Valley will all see some smoke. The greatest impacts will be in the western foothills of the Cascades and along the river valleys where drainage flows bring smoke down from the fires. Portland may see concentrations in the "Unhealthy for Sensitive Groups" and Eugene may see concentrations in the "Unhealthy for all Groups". Communities along the Santiam River from Detroit to Lyons will also see unhealthy concentrations of smoke, but as the smoke moves into Salem, the smoke tends to spread and dilute as it disperses, thus impacts in Salem will likely only be moderate. Smoke will start to clear out of the the Willamette Valley during the evening but may take until Sunday to fully clear out.
In southwestern Oregon, the Rogue Valley, Illinois Valley are expected to reach moderate conditions.
The coastal communities of Gold Beach and Brookings should expected to see light to moderate smoke in the morning but should clear out in the afternoon as winds shift to the east. Smoke is expected to remain over the rest of southwestern Oregon until Sunday.
Central Oregon will have variable conditions depending upon one's particularly location downwind of the fires Wind direction is expected to change throughout the day bringing changing concentrations of smoke. The Desolation fire located off of Hwy 26 on the Ochoco National Forecst is likely to bring smoke into Prineville, Redmond and Bend at times throughout the day. Overnight drainage flows are still likely to bring smoke into Sisters overnight and in the morning, but should clear out by mid to late morning when the inversion breaks. Klamath Falls and Lakeview should have good air quality on Saturday. Eastern Oregon will also have good air quality, although some light smoke may be present at times as the fires in Idaho will still be generating smoke..
Figure 1. 24-hour Smoke Concentrations Forecasted for the Period Ending at 5 pm on Saturday, September 16, 2017
Sunday, September 18, 2017:
A significant change in weather will occur on Sunday as southwesterly winds occur over the state accompanied by precipitation. Rain is expected to move into the State in the mid to later afternoon. By Monday morning, the Cascades may receive up to an inch of rain, as shown in Figure 2.
Figure 2. 24-hour Precipitation Excepted for the Period Ending at 5 am Monday Morning.
Smoke will clear out of the west side of the cascades on Sunday morning. As illustrated in Figure 3, by Sunday afternoon, the smoke will drift to the northeast of the fires and bring moderate levels of smoke to southwestern and central, Oregon, light smoke to eastern Oregon, and heavy smoke to Hood River and the Dalles. However, with the increasing winds speeds and the increasing change of precipitation, most of the smoke is expected to scour out of the State by Sunday evening and remain scoured out on Monday and Tuesday.
Figure 3. 24-hour Average Smoke Concentrations for the period ending at 5 pm on Sunday.
All in all, air quality should be greatly improved next week as the storms will remain with us for several days.
Please see the Air Resource Advisor forecasts for more detailed forecast for areas in the vicinity of the fires.
Disclaimer: Forecasting of weather, fire behavior, and smoke transport and dispersion is challenging. While we strive to bring you the most up to date and accurate forecasts, conditions can and do change rapidly. Please take the appropriate action to protect yourself.