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Wildfires produce pyrocumulonimbus clouds in Alaska

By Scott Bachmeier •

1-minute GOES-18 Clean Infrared Window (10.3 µm, left) images and Red Visible (0.64 µm) images with an overlay of the Fire Mask derived product (right), from 2301 UTC on 20 June to 0400 UTC on 21 June [click to play MP4 animation]

1-minute Mesoscale Domain Sector GOES-18 (GOES-West) “Clean” Infrared Window (10.3 µm) images and “Red” Visible (0.64 µm) images with an overlay of the FDCA Fire Mask derived product (above) showed that a wildfire southwest of Nenana, Alaska (METAR site PANN) produced two pyrocumulonimbus (pyroCb) clouds late in the day on 20 June 2025 . The pyroCb clouds exhibited cloud-top 10.3 µm infrared brightness temperatures (IRBTs) in the -40s C (denoted by shades of blue to cyan) — a necessary condition to be classified as a pyroCb — with the first pyroCb developing at 0027 UTC on 21 June, and the second pyroCb forming at 0226 UTC. These were the first confirmed pyroCbs in Alaska for the 2025 wildfire season.

Another wildfire just east of Healy Lake, Alaska later produced a larger pyroCb, developing at 0326 UTC (below).

1-minute GOES-18 Clean Infrared Window (10.3 µm, left) images and Red Visible (0.64 µm) images with an overlay of the Fire Mask derived product (right), from 0100-0700 UTC on 21 June [click to play MP4 animation]

The coldest cloud-top IRBT exhibited by the Healy Lake pyroCb was -57.12 C at 0607 UTC (below) — colder than the -43.66 C and -49.01 C IRBTs for the two pyroCbs produced by the wildfire southwest of Nenana.

GOES-18 Clean Infrared Window (10.3 µm, left) image and Red Visible (0.64 µm) image + Fire Mask derived product (right) at 0607 UTC on 21 June, with a cursor sample of the coldest pyroCb cloud-top infrared brightness temperature [click to enlarge]

Categories: Fire detection, GOES-18