<p>It is reported in the media that currently in Australia there are dozens of wildfires caused by lightning strikes. I am familiar with the mechanism of ordinary British lightning involving cumulonimbus and moisture, but I don't understand the Australian mechanism where hot,bone dry conditions cause lightning strikes on a massive scale, apparently from cloudless or near cloudless skies. The role of high temperatures and near cloudless skies obviously makes vegetation highly inflammable, but solar radiation hot enough to heat it to ignition temperature would kill everyone in Australia, so contrary to what some people appear to believe it can't be that. Perhaps someone can offer an explanation.</p>

CC BY-SA 4.0
2019-12-27T21:14:06.577Z
This looks suspiciously like conventional cumulonimbus which I already understand. As I said in my question, it is the moisture-free Australian lightning which needs explanation.
Michael Walsby
CC BY-SA 4.0
2019-12-28T19:46:45.883Z
I think the problem might be the assumption of completely cloudless skies.  The western US is, I'm told, quite similar to much of Australia.  While skies here are generally clear in summer, and the relative humidity is low, quite often cumulonimbus clouds build up in the afternoon, leading to lightning that sparks wildfires.  There may not be rain associated with these clouds, or the rain may not reach the ground (https://en.wikipedia.org/wiki/Virga ) The storms can also be scattered events, with plenty of clear sky between.
jamesqf
CC BY-SA 4.0
2019-12-28T20:22:35.983Z
To make th comparison more valid you need to wit until there is a long drought in western USA which bakes the vegetation and makes it very combustible. In UK long droughts are accompanied  by day after day of clear skies, as in 1976 and in lesser droughts since..
Michael Walsby
CC BY-SA 4.0
2019-12-29T05:06:48.863Z
@Michael Walsby: In the western US (or at least the Great Basin and adjacent parts), that period of long drought is called "summer".  Also quite often much of spring & fall: https://www.usclimatedata.com/climate/nevada/united-states/3198  FWIW, wildfires can happen any time of year.  I've had to evacuate for one in January.  (Started by careless disposal of fireplace ashes, though, not lightning.)
jamesqf
CC BY-SA 4.0
2019-12-29T09:02:16.840Z
What I don't understand is why people living in fire prone areas allow trees and brush to grow right up to their back doors. surely, that's asking for trouble.
Michael Walsby
CC BY-SA 4.0
2019-12-29T09:21:17.547Z
There are limits to how far fire can jump, and strong winds are not guaranteed.
Michael Walsby
CC BY-SA 4.0
2019-12-29T18:57:48.923Z
@Michael Walsby: Of course there are limits, but those limits are further than you might think.  The local fire services state that embers from a fire can easily travel over a mile and start new fires.  I've seen it happen over about a quarter of that distance.
jamesqf
CC BY-SA 4.0
2019-12-30T07:42:40.207Z
A fire creates its own winds if it is intense enough. That's why firestorms are called firestorms. The updraft causes gales or hurricanes in the streets, and people are sucked or blown into the flames. That's why Dresden, Hamburg, Darmstadt etc were different from London. But the winds are from the periphery towards the centre of the fire. I wondered whether wildfires could reach that intensity. The updraft rises to great heights, rather like a cumulonimbus cloud..
Michael Walsby
<meteorology><lightning><drought><wildfire>
Large Scale lightning Strikes from Cloudless or Near Coudless Skies. How Does it Work?
Michael Walsby
# Large Scale lightning Strikes from Cloudless or Near Coudless Skies. How Does it Work?

(Asked by: username_0 on 2019-12-27)

It is reported in the media that currently in Australia there are dozens of wildfires caused by lightning strikes. I am familiar with the mechanism of ordinary British lightning involving cumulonimbus and moisture, but I don't understand the Australian mechanism where hot,bone dry conditions cause lightning strikes on a massive scale, apparently from cloudless or near cloudless skies. The role of high temperatures and near cloudless skies obviously makes vegetation highly inflammable, but solar radiation hot enough to heat it to ignition temperature would kill everyone in Australia, so contrary to what some people appear to believe it can't be that. Perhaps someone can offer an explanation.

**Tags:** meteorology, lightning, drought, wildfire

> **Comments:**
> **username_0**: This looks suspiciously like conventional cumulonimbus which I already understand. As I said in my question, it is the moisture-free Australian lightning which needs explanation.  
> **username_1**: I think the problem might be the assumption of completely cloudless skies.  The western US is, I'm told, quite similar to much of Australia.  While skies here are generally clear in summer, and the relative humidity is low, quite often cumulonimbus clouds build up in the afternoon, leading to lightning that sparks wildfires.  There may not be rain associated with these clouds, or the rain may not reach the ground (https://en.wikipedia.org/wiki/Virga ) The storms can also be scattered events, with plenty of clear sky between.  
> **username_0**: To make th comparison more valid you need to wit until there is a long drought in western USA which bakes the vegetation and makes it very combustible. In UK long droughts are accompanied  by day after day of clear skies, as in 1976 and in lesser droughts since..  
> **username_1**: @username_0: In the western US (or at least the Great Basin and adjacent parts), that period of long drought is called "summer".  Also quite often much of spring & fall: https://www.usclimatedata.com/climate/nevada/united-states/3198  FWIW, wildfires can happen any time of year.  I've had to evacuate for one in January.  (Started by careless disposal of fireplace ashes, though, not lightning.)  
> **username_0**: What I don't understand is why people living in fire prone areas allow trees and brush to grow right up to their back doors. surely, that's asking for trouble.  
> **username_0**: There are limits to how far fire can jump, and strong winds are not guaranteed.  
> **username_1**: @username_0: Of course there are limits, but those limits are further than you might think.  The local fire services state that embers from a fire can easily travel over a mile and start new fires.  I've seen it happen over about a quarter of that distance.  
> **username_0**: A fire creates its own winds if it is intense enough. That's why firestorms are called firestorms. The updraft causes gales or hurricanes in the streets, and people are sucked or blown into the flames. That's why Dresden, Hamburg, Darmstadt etc were different from London. But the winds are from the periphery towards the centre of the fire. I wondered whether wildfires could reach that intensity. The updraft rises to great heights, rather like a cumulonimbus cloud..  

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## 0 answers

