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Pyrocumulonimbus cloud produced by the Bootleg Fire in Oregon

By Scott Bachmeier •

GOES-17 "Red" Visible (0.64 µm, top left), Shortwave Infrared (3.9 µm, top right), "Clean" Infrared Window (10.35 µm, bottom left) and Fire Temperature RGB (bottom right) [click to play animation | MP4]

GOES-17 “Red” Visible (0.64 µm, top left), Shortwave Infrared (3.9 µm, top right), “Clean” Infrared Window (10.35 µm, bottom left) and Fire Temperature RGB (bottom right) [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm), “Clean” Infrared Window (10.35 µm) and Fire Temperature RGB images (above) revealed that the Bootleg Fire in far southern Oregon produced a pyrocumulonimbus (pyroCb) cloud — denoted by cloud-top 10.35 µm infrared brightness temperatures of -40ºC and colder (darker blue pixels) — late in the day on 14 July 2021. The maximum surface 3.9 µm brightness temperature sensed with this fire was 138.7ºC — which is the saturation temperature for the ABI Band 7 detectors.

A plot of 00 UTC rawinsonde data from nearby Medford, Oregon (below) indicated that the -40ºC temperature closely corresponded to the height of the tropopause and the Most Unstable (MU) air parcel Equilibrium Level (EL).

Plot of 00 UTC rawinsonde data from Medford, Oregon [click to enlarge]

Plot of 00 UTC rawinsonde data from Medford, Oregon [click to enlarge]

On the following morning, signatures of the upper-tropospheric/lower-stratospheric smoke that was forced aloft by the pyroCb cloud could be seen arcing east-southeastward over parts of Idaho, Montana and Wyoming on GOES-17 Visible and Near-Infrared “Cirrus” (1.37 µm) images (below). The smoke signature in 1.37 µm images was not due to the plume being composed of ice particles; rather, the Cirrus imagery is also able to highlight the presence of particles that are highly effective at scattering sunlight (which includes ice crystals, dust, volcanic ash, smoke) — and the smoke signature was also further highlighted by a favorable forward scattering angle.

GOES-17 "Red" Visible (0.64 µm, top) and Near-Infrared "Cirrus" (1.37 µm, bottom) images [click to play animation | MP4]

GOES-17 “Red” Visible (0.64 µm, top) and Near-Infrared “Cirrus” (1.37 µm, bottom) images [click to play animation | MP4]

Categories: Fire detection, GOES-17