Where is the heaviest rainfall in Southern California? The peaks and canyons of the San Gabriel Mountains and its foothill cities top the list.
New dynamic data from the current rain year that spans from Oct. 1, 2016 to Sept. 30, 2017 indicates a moderate to exceptional rainy season so far — again depending on where you live — with considerable variations. After the San Gabriel Mountains, next on the list is the Santa Monica Mountains and San Bernardino Mountains.
In downtown Los Angeles, 15.44 inches have fallen this season above the average annual amount of 14.93 inches. More rain on Monday could increase that amount.
“If we had no more rain for the rest of the rain season, we would still be above normal,” said Jaymie Laber, hydrologist with the National Weather Service in Los Angeles/Oxnard.
Rain storms usually move west to east out of the Pacific Ocean. As they approach higher elevations, the colder air wrings more rain out of the clouds, a phenomenon called orographic enhancement.
“When they hit the foothills and then the mountains, they are forced up and over the mountains. The water is squeezed out of the clouds and you get more rain,” he said.
What area has the most rainfall this season?
The most rainfall in Southern California this season fell in Opids Camp, a one-time stopover during the Great Hiking Era of 1900-1940 located in a sylvan glen of spruce, maples, oaks and bay trees surrounded by a year-round stream. The former camp is located in the upper West Fork of the San Gabriel River, not far from Red Box and Angeles Crest Highway in the Angeles National Forest, above Pasadena and La Canada Flintridge.
It has already seen nearly 32 inches of rain this season.
JPL Climatologist Bill Patzert says it’s not uncommon during wetter years for Opids to receive a lot more rain. Patzert said in 2005, the last record rainy year, Opids received about 100 inches of rain. “Opids Camp is in a canyon so the rain comes across the mountain and drops into the canyon. It is what we call a micro-climate,” Patzert said.
Foothill cities drenched
Mountain and foothill spots have cleared 20 or more inches, including north Azusa, Devore, San Antonio Heights, San Dimas, La Verne and Chatsworth. Coastal cities with low elevations get less rain, Laber explained. Huntington Beach averages 13 inches a year and Seal Beach about 14 inches, less than downtown Los Angeles.
Most San Gabriel Valley cities are exceeding their annual averages: Alhambra, Pasadena, El Monte. These are affected by the orographic effect.
“The coastal areas that get less are because they are flatter,” Laber said. One exception is San Clemente with 21 inches, more than seven inches above its annual average. Sometimes a storm can unleash a thunderstorm, pouring rain on a limited area, he said.
With Death Valley, below sea level, getting the least amount of rain it makes sense that other high-desert areas also experience less rain than their mountain or valley counterparts. “Once the storms go over the San Gabriels they’ve dropped all their rain,” Patzert said.
Storms heading into the Inland Empire get blocked by mountains on three sides, decreasing rain totals, Patzert said. Riverside is in a cul-de-sac, cut off from heavy rain storm, he added.
But there’s no doubt the 2016-17 rain season has been above average with the traditionally rainiest months to come. Rain in Southern California is not atypical. Most mislabel the region as a desert. It is a Mediterranean climate with coastlines, foothills, mountains, rain forests and deserts all in one, making for numerous micro-climates and huge swings in rainfall intensity that can make water management difficult.
Here’s a look at how much rain has fallen this year so far and where, according to rain gauges kept by the NWS. All totals are season-to-date:
Top 10:
1. 31.95 inches. Opids Camp. 18.35 inches in last 28 days. Just south of Angeles Crest Highway in Angeles National Forest, north of San Gabriel Peak
2. 31.65 inches. San Gabriel Powerhouse; 18.38 inches in last 28 days. Just north of Azusa, near the intersection of Highway 39 and Ranch Road.
3. 31.49 inches. Camp Hi Hill. 17.67 inches in last 28 days. Just east of Mt. Markham and Red Box Picnic Area, Angeles National Forest.
4. 28.22 inches. San Dimas Fire Station No. 64. 13.77 inches in last 28 days. South Walnut Avenue, San Dimas.
5. 27.17 inches. San Antonio/Sierra Power House. 15.5 inches in last 28 days. Off Mt. Baldy Road, Angeles National Forest, north of Upland.
6. 26.10 inches. San Gabriel Dam. 16.77 inches in last 28 days. Angeles National Forest, Highway 39, north of Azusa
7. 25.05 inches. Chatsworth. Nearly 8 inches in last 28 days. Near intersection of Valley Circle Boulevard and Devonshire Street.
8. 24.80. Clear Creek-City School. 13.62 inches in last 28 days. Off Angeles Forest Highway north of La Crescenta in Angeles National Forest.
9. 24.70 inches. Devore Fire Station. 15 inches in last 28 days.
10. 24.67 inches. Manzanita Flats, San Bernardino National Forest. 12.16 inches in last 28 days.
Cities in Los Angeles County:
Seasonal Totals + rain in last 28 days + location/Average Annual Precipitation
1. 25.05 inches. Chatsworth. Nearly 8 inches in last 28 days. Annual average: 17.93 inches annual average
2. 22.24 inches. Alhambra. 9.13 inches in last 28 days. Los Angeles County Department of Public Works headquarters on Fremont Avenue. Annual average: 15.32 inches annual average
3. 20.91 inches. San Dimas Dam. 13.19 inches in last 28 days. Near Marshall Canyon in La Verne. Annual average: 22.6 inches annual average
4. 18.31 inches. Pasadena. 10.33 inches in last 28 days. Annual average: 17.9 inches annual average
5. 17.23 inches. Descanso Gardens, La Cañada Flintridge. 9,39 inches in last 28 days. Annual average: 23.3 inches annual average
6. 16.42 inches. El Monte Fire Station No. 166, El Monte. Nearly 10 inches in last 28 days. Annual average: 14.03 inches annual average
7. 15.52 inches. Montebello Fire Department, Montebello. 8.34 inches in last 28 days. Annual average: 14.03 inches annual average
8. 15.44 inches. Downtown Los Angeles; 8.26 inches in last 28 days Near Los Angeles City Hall. Annual average: 14.93 inches annual average
9. 15.04 inches. Redondo Beach. 8.98 inches in last 28 days. Annual average: 13.89 inches annual average
10. 14.48 inches. San Fernando Power House, San Fernando. 8.93 inches in last 28 days. Annual average: 13.02 inches annual average
11. 13.92 inches. Rolling Hills Fire Station No. 56. 7.2 inches in last 28 days. Annual average: 13.89 inches annual average
12. 13.82 inches. Signal Hill. 7.95 inches in last 28 days. Annual average: 14.45 inches annual average
13. 13.47 inches. L.A. River at Wardlow, Long Beach. 7.78 inches in last 28 days. Annual average: 14.45 inches annual average
14. 13.11 inches. Newhall Fire Station, Santa Clarita. 8.11 inches in last 28 days. Annual average: 18.2 inches annual average
15. 11.95 inches. Pierce College, Woodland Hills. 6.83 inches in last 28 days. Annual average: 16.86 annual average
Cities in San Bernardino County:
Seasonal Totals + rain in last 28 days + location/Average Annual Precipitation
1. 24.67 inches. Manzanita Flats, San Bernardino National Forest. 12.93 inches in 28-day period. Annual average: NA
2. 21.98 inches. San Antonio Heights. 15.52 inches in last 28 days. North of 210 near foothills and north of W. 25th Street. Annual average: 15.04 inches annual average
3. 19.70 inches. North Rancho Cucamonga. 11.46 inches in last 28 days. Near Hellman Avenue and Hillside Road. Annual average: 15.04 inches annual average
4. 14.77 inches. Lytle Creek Detention Basin. 7.58 inches in last 28 days. Annual average: 22.61 annual average
Cities in Riverside County:
Seasonal Totals + rain in last 28 days + location/Average Annual Precipitation
1. 16.10 inches. Beaumont. 7.73 inches in last 28 days. Annual average: 12.51 inches annual average 2. 10.36 inches in Riverside near Fairmount Park. 576 inches in last 28 days. Annual average: 12.4 inches annual average
Cities in Orange County
Seasonal Totals + rain in last 28 days + location/Average Annual Precipitation
1. 21.27 inches. San Clemente. 6.82 inches in last 28 days. Annual average: 13.99 inches annual average
2. 16.34 inches. Fullerton, at Fullerton Reservoir. 8.63 inches in last 28 days. Annual average: 13.88 inches annual average 3. 14.78 inches. Brea Dam, Brea. 6.49 inches in last 28 days. Annual average: 13.88 inches annual average
4. 12.30 inches. Villa Park Reservoir. 6.49 inches in last 28 days. East of E. Santiago Canyon Road. Annual average: 13.43 inches annual average
5. 11.75 inches. Santa Ana at 5th Street. 6.25 inches in last 28 days. Annual average: 13.33 inches
Sources: Watershed Protection District; National Oceanic and Atmospheric Administration (NOAA); National Weather Service
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