Two main things that dominate the California summers are high heat and dry conditions. When these conditions are combined with strong winds, this can create dangerous fire weather across California and even into Oregon and Washington. Stay up to date on where the fires are by checking InciWeb often during the West Coast fire season – which can last into October.
A common atmospheric setup associated with high fire risk is a ridge of high pressure sitting over the Western states that allows for sunny skies with dry conditions and increasing temperatures. The image below shows the 500mb ridge from the Tropical Tidbits Forecast Models.
On Aug 7th, 2018, the Western Weather Headquarters page shows much of the West Coast under Excessive Heat warnings, watches, and advisories with parts of California remaining under Air Quality alerts due to the wildfire smoke. Red Flag Warnings (or high fire risk) also covered much of the West Coast.
Hot temperatures and dry conditions allow the vegetation (commonly referred to as fuel) to ignite more easily. Plus, there’s an increased risk for downed power lines or trees when winds are strong – resulting in tree branches falling onto power lines and threatening the likelihood for sparking fires.
California and the Desert Southwest can also get dry lightning events in the summer and into fall. With the combination of strong winds, hot temperatures, and dry conditions, the fires can spread rapidly and be difficult to contain by fire management. When firefighters are battling numerous fires, they are desperately waiting for a low pressure system to move onshore pulling in moisture from the Pacific Ocean and bringing cooler temperatures to the region.