#pyrocumulonimbus

Des dizaines de milliers de personnes ont été évacuées de la région de Bordeaux, alors que la France lutte contre des incendies de forêt alimentés par un phénomène météorologique rare mais de plus en plus fréquent : les nuages pyrocumulonimbus, également appelés « tempêtes générées par le feu ». Ces nuages, qui se forment à partir de la chaleur intense des incendies, créent leur propre système de…

Pics taken Friday night.

Cr: Alerte Météo Gironde

(via What is a ‘fire cloud’)

In a nutshell, pyrocumulonimbus, or “pyroCb” clouds, are gigantic storm clouds that are generated by a wildfire.

Massive wildfires emit large amounts of energy and heat that rapidly rise in a smoke plume. When the fire plume rises high enough, low atmospheric pressure causes its air to cool, and the moisture condenses and forms a cloud. Such clouds can generate lightning strikes and windy conditions.

If a wildfire is sufficiently large and intense, the smoke plume it generates can form a pyrocumulonimbus cloud, which can reach altitudes of 10–15km (six to nine miles) and penetrate the stratosphere. Nasa calls them the “fire-breathing dragon of clouds”.

وقال مسؤولون إن السحب الركامية البركانية – وهي سحابة رعدية تنشأ عن الحرارة الشديدة – هي ظاهرة يمكن أن تثير حرائق جديدة وهي “غير مسبوقة في فرنسا”. مصدر الخبر

Basically, a thunderstorm is created by hot air rising, and cold air meeting it in the middle. Sometimes, when two different air masses love each other very much, they do, well...a special kind of dance. A few hours later, a thunderstorm is born.

Now, when something like a big enough wildfire, volcanic eruption or even a nuclear detonation occurs, this expedites the process, because the air is much, MUCH hotter on the ground, and rising much more rapidly and consistently. Occasionally, when conditions are just right, you get one of these:

This is a pyrocumulonimbus cloud. Literally a Cumulonimbus created by the intense heat of a wildfire.

This is Hiroshima three hours after the attack in 1945. That's not a mushroom cloud, but a thunderstorm that spawned shortly after, due to the intense heat from the blast, and subsequent fires afterwards.

And this is Japan's Sakurajima Volcano from 2016.

Now, these storms can produce precipitation such as the famous black rain in Hiroshima and Nagasaki, which was rain mixed with the dust and ash from the explosion. They can also produce lightning, as well as tornadoes.

Not like this. This is a fire whirl, which is a phenomenon known as an Eddy. This is basically when wind flows over an obstacle, and a little bit dips behind it to create a swirl. When you see garbage get picked up and start swirling around in a plaza, that's an example.

No, I mean one of these. This was from the 2003 Canberra firestorm, which produced a pyrocumulonimbus cloud overhead that then spawned an EF3 tornado.