The San Diego County wildfires are expected to affect air quality from Los Angeles to southern Arizona over the weekend as a shift in wind pushes smoke and ash away from the ocean and onto land.
By Friday afternoon, the air hanging over Los Angeles was considered "unhealthy" by the South Coast Air Quality Management District, triggering an advisory by the agency for anyone outdoors to avoid prolonged strenuous activity.
Four of the five regions in the nation with the worst air quality Saturday are forecast to be in California and Arizona – all affected by the San Diego wildfires, according to AirNow, a website that combines data from county, state and federal air quality agencies nationwide.
Air quality is expected to be unhealthiest in Cowtown, Ariz., followed by three areas in San Bernardino County. After days of Santa Ana winds pushing the smoke and ash out to sea – and the flames toward residents in San Marcos – a pressure system has reversed the wind, sending smoke back toward land, according to the National Weather Service.
Although the shift is bringing cooler temperatures and moisture – both of which will benefit firefighters – a diluted form of the fire's smoke and ash will be in the air.
In most places the air quality is expected to be moderate – meaning that only people with particular susceptibility to pollution should limit their outdoor activities. But in some places – like in Escondido – the air is expected to be unhealthy for everyone on Saturday.