Why Wildfire Relief Is Nearly Impossible This Time of Year in California

Tom Moore
Published: July 26,2016
California wildfires often become massive infernos that destroy lives and livelihoods, especially during the summer and fall months. Because of a drought that has persisted since 2012, the fire season seems to be expanding, with some fires even occurring during the winter months.
Rain is more common in California during the winter, but summer is a dry season and offers almost no relief to any fires when they're ignited.
(MORE: Residents Allowed to Return Home as Sand Fire Moves Away From Neighborhoods)

Average monthly precipitation in San Francisco. Note the dry season, which runs from May through September.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 Traditional California Fire Season

The peak time of year for California wildfires generally runs from June through October, especially across the southern half of the state. In fact, the state's 20 largest wildfires on record dating back to 1932 have all occurred during those months.
The climate over a significant portion of California is classified as "Mediterranean," meaning that most rain falls from November to early April, and the summer months are very dry. This includes metro areas like Los Angeles and San Francisco and the surrounding higher elevations.
Occasionally, monsoonal moisture works its way into Southern California during the summer months. During those periods, there can be some thunderstorms, but most produce little or no rain.
(MORE: Wildfire Burns Near Famed 'Hollywood' Sign)
These thunderstorms can produce lightning, igniting new fires and bringing strong, shifting winds which can make a wildfire behave erratically.
A summer transitions to fall, conditions remain dry from late September through at least the first half of October.

Dry California summers are the result when the jet stream ridge shifts Pacific storms well to the north.

Recipe for Wildfires

During the winter months, the jet stream often dips southward into California, allowing storms to roll in from the Pacific Ocean. In May and June, a high-pressure ridge (bulge in the jet stream) builds northward.
The result is that during the summer months, Pacific storms come in well to the north of California, and dry conditions prevail.
The ridge also produces extreme heat, especially away from the immediate coast. A pressure gradient, or a difference in air pressure, may occur between the cooler coast and hot inland areas.
(MORE: Heat to Intensify Across the West)
The result can be gusty winds, especially in higher elevations, where fires are more likely to begin. The wind direction is often out of the southwest.
As we move to September and October, Santa Ana winds become more common. These winds most often come from an easterly or northeasterly direction, and can allow any wildfires that form to rapidly spread.
All of this occurs during a season when there is no rain to mitigate the effects of wildfires.

Growing Concerns

Drought conditions have prevailed across much of California since 2012. In 2013, California recorded its driest year on record.
Lately, a ridge of high pressure aloft across the eastern Pacific has blocked storms from coming into California during the winter months. There was hope that a strong El Niño pattern during the winter of 2015-16 would produce well-above-average rainfall across California. The results were not encouraging.
(MORE: California's Erskine Fire Spotted From Space)
Parts of northern California received near average rainfall. with a few locations recording above average precipitation, during the wet season. That wasn't the case across Southern California, where many locations only received about half their average rainfall.
For example, from November 2015 through March 2016, Los Angeles received only 5.27 inches of rain, roughly half their average rainfall – 10.26 inches – during that time. Extremely dry conditions have continued into the dry summer months of 2016, and it appears that the wildfire threat is likely to become much worse as we go deeper into the fire season.
MORE: Western Wildfires in June