5 ms·

This is probably a naive question because I am not local, but how usual are wild fires during the winter? There seems to be snow large parts of the US and free

This is probably a naive question because I am not local, but how usual are wild fires during the winter? There seems to be snow large parts of the US and freezing temperatures. In LA it is currently 8°C (46°F), which is not freezing, but also not hot. Does this suggest even bigger fires are to be expected in the summer this year when it is actually hot?

eric-hu 2y ago
Grew up in LA. I don't recall wildfires in the winter, generally. There were Santa Ana Winds this past week though, and I'm pretty sure that's the cause. In the mountains near me, wind speeds were said to be 80-100 mph. They were probably lower where I am, but my neighbor's backyard canopy blew over the wall to my backyard. I helped them hoist it back over the wall today and we estimated it was about 100 lbs. These are gusty and dry winds coming from the desert, so I assume these fires spread from some manmade source. > Does this suggest even bigger fires are to be expected in the summer this year when it is actually hot? I would assume so, yes. Some insurers have been pulling out of CA in 2024.
- BlueTemplar 2y ago
  The issue here seems to be that human memory is going to be just short enough to be dangerously useless against a natural phenomenon that is decently regular, but happens in a 30 to 150 years intervals. (See also : epidemics ?)
nonelog 2y ago
I find it astounding how almost nobody points out the obvious: Arson.
harmmonica 2y ago
They rarely happen in winter (in modern times at least) because it usually rains starting in late fall. But there's been zero measurable precipitation since, I think, May 2024. It's that issue combined with the extreme winds this week that made the conditions on the ground ripe for this type of fire. Note that the winds themselves are somewhat typical (they're called Santa Ana winds and they happen every year like clockwork), but the severity of the winds this week was extreme. Don't think there have been winds as severe in decades. It was a somewhat predictable cocktail and all of these ingredients aided the severity. No moisture + high winds = high fire risk. High winds = embers easily carried forward igniting additional fires. High winds = grounded firefighting planes and helicopters.
dredmorbius 2y ago
Relatively rare, but SoCal in particular sees dry-ish winters and high, dry winds, the Santa Anas. Humidity has been in the single or low-double digits. During the recent Malibu fires I saw a 7% RH reading, in the past week ~17%. Both of those are quite dry. Much of the area sees repeat fires at ~20 year intervals or so. Several of the fire maps I was looking at were showing prior burns within the past five years, of which there were several in the vicinity of the Palisades fire. I've yet to check back to see how the burned-over areas fared in the current burn, but I'm suspecting that even recent fire activity is no longer the protection it once was. Ironically, heavy rains in recent years can also compound fire hazard as the precipitation promotes plant growth and hence fuel load. Unless rain is recent (within the past 14-30 days or so) it's not going to be protective. Keep in mind that average annual precip in Los Angeles is less than 15 inches (38 cm). San Francisco sees roughly double that, and isn't a particularly high-rainfall region itself. <https://www.laalmanac.com/weather/we13.php https://www.laalmanac.com/weather/we13.php> A midwestern location such as Chicago sees 50 inches (127 cm): <https://www.weather.gov/lot/chicago_climate_records https://www.weather.gov/lot/chicago_climate_records> Moreover, California's precipitation tends to be concentrated into a relatively small number of storms, mostly between November and May.

eric-hu 2y ago

Grew up in LA. I don't recall wildfires in the winter, generally. There were Santa Ana Winds this past week though, and I'm pretty sure that's the cause. In the mountains near me, wind speeds were said to be 80-100 mph. They were probably lower where I am, but my neighbor's backyard canopy blew over the wall to my backyard. I helped them hoist it back over the wall today and we estimated it was about 100 lbs. These are gusty and dry winds coming from the desert, so I assume these fires spread from some manmade source. > Does this suggest even bigger fires are to be expected in the summer this year when it is actually hot? I would assume so, yes. Some insurers have been pulling out of CA in 2024.

BlueTemplar 2y ago
The issue here seems to be that human memory is going to be just short enough to be dangerously useless against a natural phenomenon that is decently regular, but happens in a 30 to 150 years intervals. (See also : epidemics ?)

nonelog 2y ago

I find it astounding how almost nobody points out the obvious: Arson.

harmmonica 2y ago

They rarely happen in winter (in modern times at least) because it usually rains starting in late fall. But there's been zero measurable precipitation since, I think, May 2024. It's that issue combined with the extreme winds this week that made the conditions on the ground ripe for this type of fire. Note that the winds themselves are somewhat typical (they're called Santa Ana winds and they happen every year like clockwork), but the severity of the winds this week was extreme. Don't think there have been winds as severe in decades. It was a somewhat predictable cocktail and all of these ingredients aided the severity. No moisture + high winds = high fire risk. High winds = embers easily carried forward igniting additional fires. High winds = grounded firefighting planes and helicopters.

dredmorbius 2y ago

Relatively rare, but SoCal in particular sees dry-ish winters and high, dry winds, the Santa Anas. Humidity has been in the single or low-double digits. During the recent Malibu fires I saw a 7% RH reading, in the past week ~17%. Both of those are quite dry. Much of the area sees repeat fires at ~20 year intervals or so. Several of the fire maps I was looking at were showing prior burns within the past five years, of which there were several in the vicinity of the Palisades fire. I've yet to check back to see how the burned-over areas fared in the current burn, but I'm suspecting that even recent fire activity is no longer the protection it once was. Ironically, heavy rains in recent years can also compound fire hazard as the precipitation promotes plant growth and hence fuel load. Unless rain is recent (within the past 14-30 days or so) it's not going to be protective. Keep in mind that average annual precip in Los Angeles is less than 15 inches (38 cm). San Francisco sees roughly double that, and isn't a particularly high-rainfall region itself. <https://www.laalmanac.com/weather/we13.php https://www.laalmanac.com/weather/we13.php> A midwestern location such as Chicago sees 50 inches (127 cm): <https://www.weather.gov/lot/chicago_climate_records https://www.weather.gov/lot/chicago_climate_records> Moreover, California's precipitation tends to be concentrated into a relatively small number of storms, mostly between November and May.