Cumulonimbus flammagenitus

On 6 August 1945, an intense cumulonimbus-like cloud was photographed above Hiroshima, long after the cloud generated by the atomic bomb had dissipated. The cloud was a result of the firestorm that had by then engulfed the city.[2] Some 70,000–80,000 people, around 30% of the population of Hiroshima at the time, were killed by the blast and resultant firestorm.

Volcanic eruption plumes are not generally treated as CbFg, although they are convectively driven to a large extent[25] and for weaker eruptions may be significantly enhanced in height in convectively unstable environments.[26] However, for some months after the climactic eruption of Mt Pinatubo in the Philippines in 1991, meteorological observers from the US military observed what they termed 'volcanic thunderstorms' forming near the summit: cumulus cloud complexes formed near the top of the buoyant ash plume, and frequently developed into cumulonimbus clouds (thunderstorms).[27]

The thunderstorms often drifted away from their source region at the top of the plume, producing sometimes significant amounts of localized rainfall, "mudfall," and ash fall. They also noted that thunderstorms formed over hot flows and secondary explosions even in the absence of any eruption.[28] Further investigations confirmed that the volcano had clearly enhanced the convective environment, causing thunderstorms to form on average earlier in the day and more reliably than in surrounding areas, and that the presence of volcanic ash in cloud tops in the upper troposphere could be inferred from satellite imagery in at least one case.[21]

On 18 January 2003, a series of CbFg clouds formed from a severe wildfire, during the 2003 Canberra bushfires in Canberra, Australia.[9] This resulted in a large fire tornado, rated F3 on the Fujita scale: the first confirmed violent fire tornado.[29][30] The tornado and associated fire killed 4 people and injured 492.

On 7 February 2009, the Black Saturday bushfires killed 173 persons, destroyed over 2000 homes, burnt more than 450,000 ha, and resulted in losses of over four billion Australian dollars in Victoria, Australia. Multiple fire plumes produced a number of distinct CbFg, some of which reached heights of 15 km on that day and generated a large amount of lightning.[31]

On 30 December 2019, two fire response vehicles were overturned by what was described as a 'fire tornado' originating from an active cumulonimbus flammagenitus cloud near Jingellic, New South Wales, Australia, on a day when multiple CbFg were recorded in the neighbouring State of Victoria to an altitude of at least 16 km.[32] One of these vehicles was variously described as weighing between 8 and 12 tonnes.[10][33] The incident resulted in one fatality and injuries to two others.

Animation of the formation of a pyrocumulonimbus above the 2020 Creek Fire in California

On 4 September 2020, the Creek Fire began in the Big Creek drainage area between Shaver Lake and Huntington Lake, California. By 8 September 2020, the fire was among the 20 largest wildfires ever seen in California, with an area of 152,833 acres burnt and 0% containment.[34] The rapidly growing wildfire, aided by hot, windy, and dry weather, drought, and beetle-killed timber, created a pyrocumulonimbus cloud. According to NASA, it is the largest such cloud ever seen in the United States.[35]

Widespread cumulonimbus flammagenitus appeared over British Columbia and northwestern Alberta in connection with the 2021 British Columbia wildfires, many of which were exacerbated by the historic 2021 Western North America heat wave. In just 15 hours, between 3pm June 30 and 6am July 1, 710,117 lightning strikes were recorded, of which 112,803 were cloud-to-ground strokes.[36]

This activity followed several days of unprecedented temperature highs in late June, including Canada's highest-ever recorded temperature of 49.6°C in Lytton, British Columbia (also known as Camchin or ƛ'q'əmcín[37]).[38] At least 19 wildfires ignited between June 27 and 29, but most remained under 5 hectares (12 acres);[39] one fire, however, grew to at least 2 km² (0.77 sq mi) by June 29, prompting evacuations.[39] On June 30, two large fires spread out of control, one near Kamloops Lake which grew to 200 km² (77 sq mi) by evening, and the other north of Lillooet, which similarly grew to tens of square kilometres that day.[40][41] at least two residents were unable to escape due to the speed of the firestorm's advance and perished when a utility pole was blown down on them by flames.[42]

During the Bootleg Fire in Oregon in July 2021, an NWS forecaster told the New York Times that the fire had created pyrocumulus clouds almost daily, with some reaching as high as 30,000 feet; the fire also caused a pyrocumulonimbus cloud to form nearly 45,000 feet high, bringing lightning and rain.[43]