Once again, we are seeing a great number of fires, sweeping the western portion of North America. Fires are a natural occurrence, and good for the regeneration of hardwood forests, but with the urban sprawl moving ever deeper into the wilderness, the threat of fires to human livelihood increases, as does the threat for fires to be started by humans, either by accident, such as the Carr fire in northern California, or on purpose, such as the Holy Fire in southern California.
While the threat for fire is visceral in the west, the threat of smoke is real for much of the rest of the country, from something as simple as reduced visibility and haze, to poor air quality, respiratory issues and other safety and quality of life concerns.
The upper level pattern is fairly zonal, which is to say that the US’s upper level flow is moving predominantly west to east without many interruptions. The lone exception is a weak trough in the Pacific Northwest. The consequences are smoke pressing due eastward, right along the northern tier of states, both because of the predominant westerlies, but also because of the southerly flow within the trough, funneling California smoke in with the Washington and British Columbia haze.
One variable that helps to limit the amount of haze or smoke in the atmosphere is rainfall. It essentially cleans the skies up, as soot and smoke particles become captured in the water droplets, and the denser smoke gets scattered by updrafts. The southern US is enjoying some intermittent thunderstorms, while the threat for rain will shift northward for next week.