WILDFIRE SMOKE FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
1:30 PM PDT FRI AUG 23, 2013
SIGNIFICANT FIRE INFORMATION:
Douglas Complex Fires – Seven miles northwest of Glendale in Douglas and Josephine
Counties.
Big Windy Complex – 25 miles NW of Grants Pass; 8 miles NW of Galice.
Whiskey Complex – 6 miles east of Tiller in the Umpqua National Forest.
Government Flats Complex – 10 miles SW of The Dalles.
AIR QUALITY:
Measurement locations over the entire state of Oregon (38
total locations today) show good air quality today. Improvement in the
past 24-48 hours has been significant over the southwestern OR locations
downwind of the Douglas/Whiskey and Big Windy Complexes, as well as The Dalles
area as a wind direction shift to westerly/NWly has occurred there. The exit of
an upper-level wave to the northeast over the last 12-18 hours has helped lead
to the air quality improvement and a reduction in elevated smoke over much of
the state.
SMOKE DISPERSION FORECAST:
Wildfire smoke dispersion depends on the stability
of the atmosphere as well as wind direction and speed. A stable
atmosphere holds smoke to the ground and an unstable atmosphere allows smoke to
rise and dissipate. Smoke is typically mixed to higher altitudes during
the afternoon, when daytime heating destabilizes the air mass.
Conversely, smoke tends to settle near the ground and in drainages during the overnight
and early morning hours.
TODAY:
Clearing and improvement in air quality has been the
trend over the last 12-18 hours over much of the state, and any major reversal
of this trend is unlikely over the next several days barring additional major
ignitions. Residual low clouds remain only over portions of western OR.
Transport winds have switched to mostly southwesterly for much of the state.
Smoke production for the Government Flats Complex likely remains significant
but is now moving generally to the east/SE into areas of no air quality
measurements; it is likely air quality is still being impacted negatively
immediately east and southeast of this complex.
Saturday and Sunday:
Upper southwesterly flow will dominate the picture
through the weekend ahead of a deep eastern Pacific trough, with transport
winds generally having a significant westerly component. This will lead to a
continuation of local air quality impacts immediately NE-E-SE of active fire
zones, especially the Government Flats Complex. Otherwise, good air quality
conditions are expected to continue. The flow aloft will contain enough
moisture that late-day shower/thunderstorm activity is likely to be generated
over many higher terrain areas of the state both days, especially the Cascade
Range. Additional lightning ignitions are possible in these areas although many
of the strikes are likely to be accompanied by rain, and we are generally
seeing better low-level moisture conditions currently than we’ve seen in quite
some time. In fact a return to Red Flag conditions is unlikely for any areas of
the state as a general cooling trend at the surface is in place.
EXTENDED OUTLOOK:
The deep eastern Pacific trough will persist at least
through next Tuesday August 27, with some ejecting waves generating late-day
shower/thunderstorm activity over western and central OR, especially over
higher terrain. While some recovery in afternoon temperatures is expected over
eastern portions of the state, a return to hot/dry conditions is not likely. We
do not anticipate air quality impacts from smoke unless there are major new
ignitions or if the Government Flats Complex continues to generate significant
smoke. In the latter case the impacts would likely be confined to the east of
the fires and local areas of poor ventilation close to the fires.
This bulletin is also available on the web at
ODF Smoke Management Meteorologist
