Pyrocumulonimbus clouds as a result of bushfires in Australia


I was hiking with a friend this weekend in Ansel Adams Wilderness in the eastern Sierra. This was our view as we entered the wilderness. Note the clear blue sky!

Gem Lake Saturday, Sept 5, 2020

Over the course of the day as we hiked our loop, we noticed more smoke. “Must be the Slink Fire or something”, I thought. Which was pretty far away but hey, winds can carry smoke long distances.

As we were taking a break around 2pm, we heard some thunder in the direction of the smoke. The wind picked up, and the temperature dropped. We were only day hiking and didn’t have our full overnight load out, so we jumped up and started the 5m hike back out to avoid being caught in a storm.

Here’s the best photo I could find. Note the smoke/cloud front halfway across the sky as we hiked out:

Agnew Lake Saturday, Sept 5, 2020

I remember looking at the weather radar on my phone and wondering why the green/yellow precipitation blob suddenly seemed to appear around 2pm from a totally clear sky.

Of course, we later discovered it was due to the new Creek Fire burning near Shaver Lake.

Turns out, this is a well-understood phenomena that I had not previously heard of. A bit of research led me to discover Pyrocumulonimbus clouds. From wikipedia:

The cumulonimbus flammagenitus cloud (CbFg), also known as the pyrocumulonimbus cloud, is a type of cumulonimbus cloud that forms above a source of heat, such as a wildfire or volcanic eruption,[5] and may sometimes even extinguish the fire that formed it.

One of the most striking examples of this phenomena I could find was the result of the Atomic Bomb strike on Hiroshima. This photo is of a pyrocumulonimbus cloud, often mistakenly identified as the fallout from the bomb itself:

As we endure a terrible wildfire season here in California, I’d love to see any other striking examples of this. The more you know!

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Dave Paola