Pyrocumulonimbus clouds in Colorado and California
GOES-16 (GOES-East) “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed 2 pulses of pyro-convection emanating from the Williams Fork Fire that was burning between between Kremmling (K20V) and Berthoud Pass (K0CO) in Colorado on 14 August 2020. The cloud of the second pulse, originating around 2300 UTC, exhibited infrared brightness temperatures of -40ºC and colder (shades of blue in the 10.35 µm images) — assuring the heterogeneous nucleation of all supercooled water droplets to form ice crystals, and thereby meeting the criteria of a pyrocumulonimbus (pyroCb). The pyroCb then drifted east-southeastward across Colorado.
The coldest pyroCb infrared brightness temperature was -46ºC, which corresponded to an altitude near 11 km according to rawinsonde data from Denver (below).
===== 15 August Update =====On the following day, 1-minute Mesoscale Domain Sector GOES-16 (GOES-East) Visible, Shortwave Infrared and Infrared images (above) showed another pyroCb that developed around 2240 UTC. This pyroCb moved southeastward, exhibiting cloud-top infrared brightness temperatures as cold as -55ºC — which, according to rawinsonde data from Denver (below) represented an altitude near 12 km. Farther to the west, the Loyalton Fire was burning in northern California, near the border with Nevada. 1-minute Mesoscale Domain Sector GOES-17 (GOES-West) Visible, Shortwave Infrared, Infrared Window and Fire Temperature Red-Green-Blue (RGB) images (below) showed that this fire produced a pyroCb cloud around 2100 UTC, which then drifted northeastward across the California/Nevada border. This event exhibited extreme fire behavior, producing fire whirls and prompting NWS Reno to issue a Tornado Warning for the source region of the pyroCb at 2135 UTC. The cloud-top infrared brightness temperatures of the pyroCb were around -55ºC; rawinsonde data from Reno (below) indicated that this corresponded to an altitude near 12 km.