Wildfires rage in Pacific Northwest
Driven by a dry summer, numerous fires have been ignited in the Pacific northwest of the United States and far southwestern Canada. These fires were largely ignited by lightning from late summer storms, but continued drying in the area has both increased susceptibility to fire while also preventing rain from quenching the flames. The largest fire, Bear Gulch Fire on the Olympic Peninsula, has grown to over 9400 acres while containment holds steady at around 10%. The true color RGB from GOES-18 as displayed on CSPP Geosphere clearly shows the nearly state-wide extent of the smoke on an otherwise cloud-free day.
The GOES Fire Temperature RGB product (described here) uses a combination of the 3.9, 2.2, and 1.6 micron channels to provide a qualitative assessment of fire temperature. Since these are shortwave channels, they are subject to solar reflectance. However, the brightness temperatures of fires are so great that they can still be seen in the day. The hotter a fire is, the more emission it produces at the shorter wavelengths. When those three channels are combined into an RGB recipe, the fire hot spots change from red to yellow to white with increasing fire temperature as more influence from those shorter-wavelength channels is present.
This animation below shows the Fire Temperature RGB product in action. Note the numerous red dots across the region.
However, the Bear Gulch Fire is hardly visible via this product despite being the largest fire in the state of Washington. Located southwest of Seattle on the Olympic Peninsula, this fire is only intermittently present on the RGB product. Zooming in on the target area helps emphasize this as the bright red dot representing the fire only appears briefly over the course of a 2+ hour long animation.
The reason for this has to do, in part, with the unique terrain of the region. The GOES aerosol optical depth product vividly indicates just how extensive the smoke is across the state of Washington. However, the plume from the Bear Gulch Fire (seen as the red area in western Washington just west of Puget Sound in the below movie) has a much smaller extent than many of the other, smaller fires. This is because the mountainous terrain is largely trapping the smoke.
This trapped smoke results in a higher optical depth than in other locations, which then obscures the infrared emission from the fire. As a result, the 3.9 micron channel view of the fire is largely insensitive to the fire’s high temperatures; only occasionally does the smoke plume abate enough to enable some of that intense radiant energy to escape to space.
