Lingering smoke from Fourth of July fireworks triggered a hazardous air quality alert across the region that lasted until 3 p.m. Sunday, July 5, and a building heat wave will push temperatures well above normal through the rest of the week, forecasters say.
Santa Monica recorded 67 degrees early Sunday morning with low coastal clouds beginning to clear, according to KTLA meteorologist Kirk Hawkins. While inland communities including Altadena, El Monte, Jurupa Valley, Rancho Cucamonga, Redlands and Hesperia showed unhealthy air quality readings on monitors Sunday morning, the coast fared better as marine air moved in.
But the clearing wasn't as strong as usual. National Weather Service meteorologist Carol Ciliberti said the same high-pressure system driving the incoming heat is trapping particulate matter near the ground.
"If we had stronger onshore flow, that would help to disperse some of the fine particle pollution," Ciliberti said. "That's not happening."
The South Coast Air Quality Management District issued the hazardous air quality alert Saturday evening, July 4, due to soot and particulates from fireworks. The alert ended at 3 p.m. Sunday, July 5, for central and southern Los Angeles County, northern Orange County, and Riverside and San Bernardino counties. July 4 and 5 are traditionally two of the worst air quality days of the year for the region, according to the South Coast AQMD.
The poor conditions were compounded by a late June warehouse fire in Boyle Heights that released extraordinary amounts of soot across L.A. County, on par with wildfire-level pollution from the previous year, the Los Angeles Times reported.
Heat advisory begins Tuesday
The National Weather Service has issued a heat advisory for Los Angeles County beginning Tuesday, July 7, through Thursday, July 9. The advisory covers the Santa Clarita Valley, the East and West San Fernando Valley, parts of the San Gabriel Valley and the Northwest L.A. County Mountains, where temperatures are forecast to reach 90 to 105 degrees.
NWS meteorologist Rose Schoenfeld said temperatures will run 5 to 10 degrees above normal for this time of year. The San Fernando Valley is forecast to hit 94 degrees Monday, July 6; 97 degrees Tuesday; and 100 degrees Wednesday, July 8, according to Hawkins.
Santa Monica residents won't face the worst of it. The coast typically runs 10 to 15 degrees cooler than inland areas, keeping highs in the low 80s this week. The L.A. Basin is forecast to reach about 84 degrees Sunday, July 5, before climbing into the mid-80s by Wednesday and Thursday.
Schoenfeld warned the relief may be short-lived, saying another heat wave is expected to develop across much of the West by the following weekend.
Who should take precautions
People with asthma or other respiratory conditions should limit prolonged outdoor activity while air quality remains poor, Hawkins said. Children, older adults and pets are also more vulnerable to smoky conditions.
As temperatures climb, forecasters advise residents to stay hydrated, avoid strenuous outdoor activity during the hottest part of the day, never leave children or pets in parked vehicles and check on older adults who may be vulnerable to heat.
Residents seeking cooling center locations can call 311 or check smgov.net for updates.
