Issued: August 29, 2017
Forecaster. R. Graw, USDA
Forest Service
Yesterday’s forecast was a bust for the Willamette Valley
resulting from the increase in fire activity associated with the thermal
trough. The increase in smoke production
combined with the delay in the wind shift is now causing unhealthy levels of air
quality throughout much of Western Oregon and the Cascades. This is illustrated in Figure 1, which was taken
from the morning overpass of the MODIS satellite. The good news, is that stronger, westerly
winds are expected to begin around 5 p.m., and should scrub out the air down to
the valley floor within a few hours, and air quality should greatly improve
later this evening for the Willamette Valley.
Figure 1. MODIS
Satellite Image from Tuesday morning, Aug. 29, 2017
Wednesday - Aug. 30, 2017
An upper level trough advances into the western portion of the state, bringing southwesterly (i.e., from the southwest) winds aloft, ahead of
the trough. As the trough advances eastward, the winds will shift, bringing
northwesterly winds across much of the state, later in the day.
This pattern will bring relief to the Oregon Coast and the
Willamette Valley but transport the smoke from the fires to the northeast
during the day, and to the southeast in the evening. Consequently, much of our state will continued
to be impacted by smoke. Figure 2 is the
Blue Sky model-predicted 24-hour smoke concentrations (in a relative sense) for
tomorrow, and Figure 3 illustrates the peak hourly concentrations that may be
expected within the forecast period. However, the shift in winds in the evening
is not depicted.
Figure 2.
Model-Predicted 24-hour average smoke concentrations for Wednesday
Aug. 30, 2017
Figure 3. Model-Predicted Maximum 1-Hour Smoke Concentrations
for Wednesday Aug. 30, 2017
Disclaimer: Due to rapidly changing conditions, the
reliability and accuracy of these forecasts may change. Updates to the forecast will be posted if
warranted. As always, please refer to the Air Resource Advisors’ reports on this blog for more detailed smoke forecasts for areas near the fires.