| Above: Darkness at noon: embers fall from burning palms and the sun is obscured by smoke as flames close in on a house at the Woolsey Fire on November 9, 2018 in Malibu, California. Image credit: David McNew/Getty Images. |
Smoke from California’s Camp Fire continues to plague central and northern California with unhealthy levels of air pollution, but relief is on the horizon--the season’s first major storm system will bring rain to the state beginning on Tuesday evening. Many schools in the San Francisco Bay and Sacramento area were closed on Friday and will also be closed on Monday and Tuesday, including UC Berkeley and UC Davis, because of pollution levels for fine particulate matter (PM2.5) in the red “Unhealthy” range.
A weak flow of air off the ocean helped reduced pollution levels over the Bay Area over the weekend, and the historic air pollution episode peaked on Thursday, Friday, and Saturday. A Berkeley Earth website that tracks global pollution showed Sacramento, California as having the worst air pollution for any major city on Earth on Friday. On Saturday, the anti-honor for most polluted city on Earth went to Oakland, California. However, by Sunday and Monday, the top ten spots on the most polluted city list were exclusively populated by the many cities in India and China that routinely see air pollution levels in the red “Unhealthy” range or purple “Very Unhealthy” range.
Fine particular air pollution for selected California cities since the start of November.
— Robert Rohde (@RARohde) November 19, 2018
It has been a long 10 days for Northern California since the start of the #CampFire. Sacramento, San Francisco, and Stockton have all recorded record high pollutant levels. pic.twitter.com/4ZqkaMHMX7
On Friday at EPA’s monitor in downtown San Francisco at 10 Arkansas Street, the 24-hour PM2.5 level was 171 μg/m3. That’s nearly five times higher than the 24-hour standard of 35 μg/m3, and well into the purple “Very Unhealthy” air regime. In EPA’s on-line records that extend back to 1999, the previous highest 24-hour PM2.5 levels were 145 μg/m3 (set on the previous day), and before that, 76.6 μg/m3 in 2001.
In Sacramento, the pollution was even worse: the 24-hour PM2.5 levels on Thursday were 263 μg/m3, in the maroon “Hazardous” range—the highest level of danger on EPA’s Air Quality Index (AQI) scale. At this level, EPA warns that “this would trigger a health warnings of emergency conditions.” The levels fell slightly to 225 μg/m3 on Friday, to the purple “Very Unhealthy” range. Over the weekend, though, pollution levels in both San Francisco and Sacramento fell into the red “Unhealthy” range, and remained there on Monday morning.
As of 10 am EST Monday, the Camp Fire near Paradise had burned 151,000 acres (17th largest in California history), and was 66% contained. The fire had destroyed 15,573 structures, making the most destructive fire in California history. At least 77 deaths were being blamed on the fire--the deadliest U.S. wildfire in 100 years.
As of 10 am EST Monday, the Woolsey Fire near Malibu had burned 97,000 acres, and was 94% contained. The fire had destroyed 1500 structures and damaged 341 more. The fire caused 3 deaths and 3 firefighter injuries.
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| Figure 1. The Air Quality Index (AQI) from wildfire smoke for fine particulate pollution (PM2.5) was in the red “Unhealthy” range (AQI above 150) over much of California on Friday morning. One monitor in Chico, nearest the Camp Fire, reported and AQI in the purple “Very Unhealthy” range (AQI above 200). Image credit: EPA. |
Dangerous air pollution to continue through Tuesday
Light winds are expected over most of California’s smoke-affected areas through Tuesday, which will be the final day of this dangerous and difficult air pollution episode for most of the affected regions. By Tuesday night, a classic fall Pacific storm system will push a band of moderate rains inland along the coast of central and northern California. These rains will reach southern California by Wednesday morning. As this rain band pushes inland on Wednesday, strong onshore winds behind the front will disperse the smoke, and the rains will wash much of the smoke out of the skies. A second storm system will move inland over Northern California on Thursday night, bringing additional rains and mountain snows to the Sierras Friday through Saturday.
Storm total rainfall forecast through Saturday morning continues to show much need rainfall to NorCal. pic.twitter.com/FR7ljR6TsQ
— NWS Bay Area (@NWSBayArea) November 18, 2018
The two storm systems are expected to deliver at least an inch of rain over much of northern and central California, including the Bay Area and Sacramento Valley. The coastal ranges and Sierra foothills below snow level should pick up generally 2 to 4 inches of rain through Friday night. Rainfall amounts in Southern California are expected to remain below 1 inch in most areas from the first storm system. Up to a foot of snow could fall in the Sierra Mountains by Saturday.
Ash and debris flows possible
The rains are expected to mobilize ash from the recent wildfires creating muddy ash flows, which are not hazardous. If the rain is heavy enough, more dangerous debris flows could result—a mass of water, loose mud, sand, soil, and rocks moving down a slope. They tend to occur over recently-burned areas whose soil can repel water as strongly as paved areas. Residents throughout and downhill from the fire-stricken areas will need to keep a close eye on the flash flood threat during the upcoming winter. Paradise normally receives 9" - 10" of rain each month from December through February.
Bob Henson contributed to this post.
