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by quarterdime 1424 days ago
As a former wildland fire fighter, I can assure you that temperature (and wind and relative humidity) have a HUGE effect on fire behavior. Furthermore temperature and relative humidity (not so much wind) have a huge impact on ignition. My training emphasized this quite heavily, but I thought the effect was exaggerated until I experienced it first hand.

In the Western US, construction, mining, forestry, etc. industries are well aware of the fire risk from routine work (construction equipment, off road vehicle traffic, chain saw work, etc.). In "red flag" conditions, there are fire watch policies. For example in forestry work, my crew would have to cease chain saw work late in the morning and stand a fire watch for 30 minutes before leaving the work site.

So as I watch the news about these fires, my first thought is ignitions: routine activities (parking a vehicle on grass, driving construction equipment, discarding a cigarette) that would be unlikely to cause a fire in normal (backward looking) UK weather conditions. My next thought is that once a fire has started, it is likely to burn hot and fast. Hotter and faster than I suspect fire fighters in London are accustomed to.

As an aside, I have been trying to figure out a good source for weather data. I see plenty of sources for temperature, but I am curious about the wind speeds and relative humidity. From the photos I am seeing, it looks like wind speeds are over 10 mph.

3 comments

^ this is why we come to hacker news. Deep contextual comments from knowledgeable professionals. Thank you.
Agreed!
In Australia during droughts there are reminders to not throw cigarette butts out the window of cars. Lightning also plays a large role in starting fires, but I also recall, as a child, being told that rubbish (litter) such as bottles and cans can reflect the harsh sunlight in a focused way and cause an ember.

I recall not buying a diesel mazda car because it had a disclaimer about not parking on long grass because of the danger of starting a fire. Apparently, mazda finally made it to recall status:

https://www.abc.net.au/news/rural/2017-12-29/ford-rangers-ma...

From the owner's manual⋮

> Parking over or near anything flammable, such as dry grass, is dangerous.

https://owners-manual.mazda.com/gen/en/cx-5/cx-5_8gj1ee18b/c...

I hope you didn't buy a gasoline vehicle instead - catalytic converters are worse.
You could try the Met Office website. This is a station in North West London

https://www.metoffice.gov.uk/weather/observations/gcpvj0v07

Humidity was about 15-20% during the afternoon, winds 13 gusting 26mph.

It was very strange this afternoon to have such a strong wind (29mph here, not in London) that was so hot (39C) I have never felt anything like it in the UK, it was like standing in front of a giant hairdryer.
Even here in Scotland I was shocked that the wind on Monday felt hot - I've never encountered that here before.

The weather over the last couple of days has felt qualitatively different - and we've had nothing like the temperatures further south.

We felt the same in the Peak District. Hot wind blowing. Then a little after the heatwave Peak it suddenly flipped to “cold, regular” wind. Surreal experience.