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Statewide Smoke Outlook for Saturday and Sunday September 9-10, 2017

Oregon State Smoke Forecast.
Issued: Friday, September 8, 2017
Forecaster:  R. Graw, USDA Forest Service

Current Conditions (Friday, September 8th):

Light to heavy rain occurred across many of the fires yesterday, bringing as  much as 1.5” of rain across parts of the Cascades and Siskiyou Mountains.  This helped decrease fire activity.   As a result, air quality was greatly improved as of this morning in western Oregon, although still remained unhealthy in Ashland, but that's an improvement over yesterday's hazardous conditions.  However, central and northeastern Oregon were in the Unhealthy category this morning, as shown in Figure 1 below.

Figure 1.  Air Quality Index as of 9:00 am Friday September 8, 2017.

Unfortunately, with all the cloud cover, the smoke models are not able to adequately detect all the fires, as the model identify the fires through their radiative power picked up by the satellites.  As such, an alternative method is needed to forecast smoke.  

Saturday:  September 9, 2017

A low pressure system will dig into the state on Saturday, as illustrated in Figure 2.   Very little precipitation is expected with this system, and only in the extreme northwest portion of the state.  However, the southeast portion of the state will also received as much as a 0.5" of rain over the Steens Mountains.  This system will bring westerly winds aloft, particularly in the northern portion of the state.  

Figure 2.  500 mb forecast map for Saturday, September 9, 2017.  

At the surface, winds will be westerly across the northern portions of the state, whereas they will be out of north in the southern portions of the state, as illustrated in Figure 3. Mixing of the atmosphere will also be marginal to good across most areas, as well, helping ventilate some areas but also enabling mixing of smoke aloft down to the surface. 

Figure 3.  Forecasted Surface-Level Winds for 2 pm on Saturday, September 9, 2017

The smoke forecast is as follows.  The northern and central coast and the Willamette Valley are expected to continue to have good air quality on Saturday.   The exception to this may be Eugene where night time drainage flows will continue to transport smoke down the McKenzie River overnight.  Area in the eastern portion of the Columbia River Gorge such as Hood River, the Dalles, and possibly as far east as Pendleton will experience degraded air quality due to the Eagle Creek Fire. Southwest Oregon will continue to experience will likely continue to remain smokey. Central Oregon communities along the eastern foothills of the Cascades will also experience smokey conditions Eastern Oregon including Baker City, Enterprise, LaGrande, and even John Day, should see improved conditions.

Sunday, September 10, 2017:

By Sunday afternoon, a ridge of high pressure will move into over the state, as illustrated in Figure 4. This will begin a warming and drying trend over the state.  Additionally this will bring a reversal of winds and a subsidence inversion leading to smokey conditions once again. 

Figure 4.  500 mb forecast map for 11 am on Sunday, September 10, 2017.

A reversal of winds is expected to develop on Sunday from the south to the north throughout the day. Figure 5 illustrates the forecasted mixing and surface winds at 2 pm on Sunday.  An east wind will occur in the Columbia River Gorge.  Over the Cascades, a convergence zone will form with east winds on the east side of the fires and a northwest wind of the west side of the fires.   Over the Chetco Bar and Miller Complex in southwestern Oregon, winds will be out of the north. Only marginal mixing is expected over most of the state.

Figure 5.  Forecasted Surface-Level Winds at 2 pm on Sunday, September 10 2017

Air quality is expected to be good over the central and northern coast. Smoke is expected to return to the Portland metropolitan areas on Sunday as the east winds bring smoke from the Eagle Creek fire to the west and then south into the Willamette Valley.  This will bring some relief to Hood River and the Dalles.   The southern portion of the Willamette Valley may not feel this smoke until later in day, if at all. 

The Rogue Valley is likely to experience degraded air quality with the return of the east winds over the Cascades.   Central Oregon and the eastern portion of the Columbia River Gorge ought to see improved air quality with the easterly winds.  Eastern Oregon should also experience good air quality, as should southern Oregon in communities like Klamath Falls, Lakeview, and Burns.

Monday September 11, 2017

Looking into next week, by Monday, the ridge will be well established over the state, continuing the hot and dry conditions.  Fires will be more active and thus producing more smoke on Monday. Easterly winds will prevail across most of the state, continuing to add smoke into the western portion of the state, but bringing favorable air quality into central and eastern Oregon.

Tuesday - September 12, 2017

The ridge starts breaking down on Tuesday as another trough of low pressure will begin to work its way into the state.  This will bring cooler and more moist air into the state, tempering fire activity, and the return of westerly winds.

Disclaimer:  Fire activity and weather conditions can and do change rapidly.  These forecasts are subject to change as well, and will be revised accordingly.

For more specific information in your geographic area, please refer to the Air Resource Advisor forecasts.