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McDonald Fire in Alaska produces 2 pyrocumulonimbus clouds

By Scott Bachmeier •

GOES-18 “Red” Visible (0.64 µm) images with an overlay of the Fire Mask derived product (top) and “Clean” Infrared Window (10.3 µm) images (bottom) [click to play animated GIF | MP4]

10-minute Full Disk scan GOES-18 (GOES-West) “Red” Visible (0.64 µm) images with an overlay of the Fire Mask derived product (a component of the GOES Fire Detection and Characterization Algorithm FDCA) and “Clean” Infrared Window (10.3 µm) images (above) showed 2 pulses of pyrocumulonimbus (pyroCb) clouds — exhibiting cloud-top infrared brightness temperatures in the -40s to -50s C, denoted by shades of blue to red in the 10.3 µm images — that were produced by the McDonald Fire (located just southeast of Fairbanks, Alaska) late in the day on 17 June 2024. As they moved eastward toward the Alaska/Yukon border, the first pyroCb reached a minimum cloud-top infrared brightness temperature of -53.7ºC, with the second pyroCb later reaching -54.4ºC.

A Suomi-NPP Infrared Window (11.45 µm) image valid at 2319 UTC on 17 June (below) captured the first pyroCb cloud not long after its formation — and included a cursor sample of cloud-top brightness temperatures for both the 11.45 µm (-55.58ºC) and the underlying 3.74 µm Shortwave Infrared image (+25.10ºC).  During the daytime, pyroCb cloud tops will usually exhibit significantly warmer Shortwave Infrared brightness temperatures, due to enhanced reflection of solar radiation off the smaller ice crystals found in the pyroCb anvil (reference).

Suomi-NPP Infrared Window (11.45 µm) image valid at 2319 UTC on 17 June, with a cursor sample of cloud-top brightness temperatures for both the 11.45 µm and the underlying 3.74 µm Shortwave Infrared image [click to enlarge]

A Landsat-9 Natural Color RGB image displayed using RealEarth (below) depicted the areal extent of the McDonald Fire burn scar (darker shades of brown) at 2105 UTC on 17 June, just prior to the flare-up of the wildfire that produced the 2 pyroCb clouds.

Landsat-9 Natural Color RGB image at 2105 UTC on 17 June [click to enlarge]

Categories: Fire detection, GOES-18, Suomi NPP, VIIRS