massive fire on belle isle rocksSubmitted by ceededcrotch t3_1200c63 in rva
wagonboss t1_jdfe7kj wrote
Reply to comment by lunar_unit in massive fire on belle isle rocks by ceededcrotch
Humidity.
humidity drops from morning through early afternoon, and the drier the air- the easier it’s spread. After 4, as the evening settles, humidity raises and doesn’t burn as easily
Source: Firefighter
Daemonrealm t1_jdfrzvp wrote
That’s a good TIL.
Charlesinrichmond t1_jdflpzk wrote
Very interesting I always thought it was the Sparks being more visible
wagonboss t1_jdh83mg wrote
Thanks to all for the upvotes, just a little more of an explanation for ya. It’s not a perfect science, and I’m not a meteorologist- so I’ll do my best. In the morning humidity is typically higher from overnight. As temperatures rise, humidity drops. When it’s below 20% and combined with dry conditions and wind, it becomes very conducive to fire spread. So the 4pm burn law was created to skip the worst of it. Usually it starts to raise before that time, but it’s a compromise as I’m sure when the law was created there was some push back. Today the humidity doesn’t dip super low, but here’s an example of it raising throughout the afternoon:
KiwiStack t1_jdgyysw wrote
Oh… this makes a lot more sense. Growing up in an area with volunteer firefighters, I always thought it was because they had more firefighters on shift after four.
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