August in Northern California is usually pretty simple in the weather department: Hot and sunny.
But not this week.
Monsoon conditions are sweeping through California as a result of an unusual combination of weather events. Dramatic summer storms from the Gulf of California, which normally confine themselves to the southwestern desert states, are pushing much farther north and bringing heavy clouds, rain, wind and lightning across the Golden State.
While the change has brought relief from relentless sun and dry conditions in California this summer, it has also brought trouble. On Sunday, 2,500 people were stranded in the small community of Forest Falls in San Bernardino County after a downpour caused a mudslide that blocked the only access road into the town and destroyed at least eight homes. Also, monsoonal storms have caused thousands of lightning strikes over the past week, adding to the extreme fire danger.
The National Weather Service is predicting as much as half an inch of rain across the northern Sierra Nevada through Tuesday evening. Isolated areas, including a region just west of Lake Tahoe in the American River watershed, could get an inch of rain.
Sacramento, which saw sprinkles on Monday, could see 0.1 inches of rain today. That isnt much, but it would be record-breaking. The most rain ever recorded on Aug. 5 in Sacramento was 0.01 inches in 1974.
Brooke Bingaman, a forecaster with the National Weather Service in Sacramento, said getting this much moisture from a monsoon pattern happens only about once every 10 years.
It is common for us to get monsoonal moisture surges during the summer, Bingaman said. What is uncommon is the amount of moisture thats coming up with this particular surge.
The storms could be either a blessing or a curse for firefighters battling several large blazes in the states northern mountains. The Eiler fire and the Bald fire, both in Shasta County, exploded in size in a matter of hours on Saturday because the vegetation is extremely dry, said Cal Fire Capt. Amy Head. Together they had burned more than 65,000 acres by Monday evening and were only minimally contained.
Head said rainfall from storms expected today could certainly help combat those fires. Even if it doesnt rain, the increased cloud cover and moisture in the air can cool things down enough to suppress fire activity. But firefighters are not counting on those benefits, she said. Theyre more worried about additional lightning strikes and high winds that often accompany monsoonal storms.
Were keeping a real close eye on the fronts of these weather systems coming through, she said. What they can do is create a lot of erratic winds and increase fire behavior. Fires that have firefighter fatalities on them have been related to these kinds of weather patterns.
Monsoon conditions start in Mexico because the land and the sea surface heat up at different rates. The summer sun evaporates water from the gulfs of Mexico and California and creates humid conditions over the land, which then produces rain. As plants begin to grow, they pull water from the soil and return it to the air. This increases humidity, fueling more rain. Then a pressure difference between the hot, parched air over the Southwestern states and cooler air over Mexico begins to pull the moisture-laden air north to Arizona and New Mexico.
This year, Bingaman said, a low-pressure storm system happens to be moving north through California at the same time. While this wouldnt normally produce much rain on its own, it is driving the monsoon farther north.
This one is a lot wetter than what we typically see, she said.
William Patzert, a climatologist at NASAs Jet Propulsion Laboratory in Pasadena, said a third factor is also in play: El Niño. This pattern, signified by a warming of the equatorial Pacific Ocean, is sometimes associated with wetter weather in California and has been predicted to occur this winter. Already, many media outlets are pointing to El Niño as a potential drought-buster, although historically it is erratic as a storm producer.
But El Niño now appears to be weakening. The equatorial Pacific has been cooling in recent weeks. Even so, Patzert said, it left behind warmer water near the Mexican coast, which has boosted humidity and added moisture to the monsoon pattern.
Although the moisture is welcome amid Californias extremely dry conditions, it will do nothing to ease the drought. That will require a full winter of wet storms.
It makes for good TV, but theres not much drought relief in this, Patzert said.
The biggest impact from the monsoons so far has been mudslides in several small communities in the mountain canyons of San Bernardino County. The worst occurred in Oak Glen and Forest Falls, where about 2,500 people became isolated when mudslides closed the only access roads.
Although emergency crews were able to restore access quickly, officials were particularly concerned about the safety of about 500 children who had just arrived at Mountain Home Conference Center in Forest Falls to begin a week-long church group retreat. While the conference center experienced minor damage, the children were sheltered in place and none were injured.
Up to eight homes near Forest Falls were likely lost and several others sustained minor damage from mud and water, fire Capt. Jeff Britton said.
Everyone in the two towns was accounted for, and no injuries were reported, officials said.
To the west, a 48-year-old man died in a car that was swept into rain-swollen Bear Creek near the town of Mount Baldy. Coroners officials identified him on Monday as Joo Hwan Lee of El Segundo.
Residents of Mount Baldy awoke Monday to sunny skies and mud-filled streets. They swapped stories between drying out carpets and shoveling dirt from the front of their homes.
The stream was a raging black torrent of debris and big logs and muddy, silty water, said Michael Honer, who watched the flood build over an hour from a friends house up the road. It was apocalyptic. It sounded like a cross between a railroad train and a jet engine.
Bear Creek, which hadnt run in the summer for two years, turned to a gusher of rocks and logs, jumping its banks and surging across the adjacent road. The gorge that had been 5 to 15 feet deep in places was filled to the banks Monday with rocks and silt and level with the road. Only a trickle of water remained.
Cal Fire officials said monsoonal storms produced thousands of lightning strikes across the state last week, and the agency responded to 250 new fires. Most were kept small through a combination of rapid response and easy access to the blazes.
The Shasta County fires have been a different story, however, because they are in very remote, steep terrain. By Monday the Eiler fire had crossed Highway 89 and burned 26,000 acres about 4 miles southeast of Burney. It had destroyed nearly 30 structures, including eight homes, and firefighters had not achieved any containment.
The Bald fire, burning about 10 miles to the northeast, was larger at about 40,000 acres and was 20 percent contained. No structures had burned.
Both fires were burning rapidly through very dry forest and causing spot fires as much as a half-mile downwind. Head, the Cal Fire captain, said such fire behavior is more typical of late summer and fall, but she called it unprecedented for this time of year.
Obviously any rain is welcome, she said. The problem is, it most likely is not going to be a significant amount of rain. It will be a minimal amount and it will help for a short period of time.
Call The Bees Matt Weiser at (916) 321-1264. Follow him on Twitter @matt_weiser. The Associated Press contributed to this report.