Two storm systems are lined up to bring 1 inch or more of rain to the Mother Lode and as much as 6 inches of snow to the Central Sierra this Friday and Sunday into Monday, forecasters say.

The wet weather expected Friday is described as weak compared with the wetter Sunday-Monday system, which could bring enough rain and runoff to raise concerns in recent burn areas, including the 57-square-mile Donnell Fire scar east of Donnell Reservoir in the Stanislaus National Forest.

“That first system is coming along the 40 North latitude about halfway between Hawaii and Alaska,” Brendon Rubin-Oster, a National Weather Service meteorologist in Sacramento, said Wednesday. “The second system appears to be originating more in the Gulf of Alaska, farther north, for the Sunday-Monday storm.”

Predicted spells of wet weather approaching this weekend are not expected to bring below-freezing temperatures to foothill towns like San Andreas, Angels Camp, Murphys, Columbia, Sonora and Jamestown, where daytime highs in the 50s to low 60s and nighttime lows in the 40s are forecast to persist into next week.

It’s going to be slightly cooler in places like Arnold and Groveland, and colder still at Pinecrest and Strawberry. Up above 8,000-foot elevations like Ebbetts Pass, Sonora Pass and Tioga Pass, it will be full-on freezing with daytime highs in the mid-30s and nighttime lows in the mid- to low 20s. Passes on highways 4, 108 and 120 are all closed for the season.

Friday’s system could bring less than 1 inch of snow to pass levels, with snow lines coming down to around 5,000 feet. The Sunday-Monday storm could bring 4 to 6 inches to Ebbetts Pass and Sonora Pass, and 2 to 3 inches to Tioga Pass.

Showers may linger into Saturday morning with some clearing in the afternoon before the Sunday-Monday storm moves in.

Minor storms in the past week and stronger storms in November have helped boost precipitation totals in Central Sierra watersheds, including the Stanislaus River and Tuolumne River drainage areas, to 93 percent of normal so far this water year.

A weak system Sunday into Monday this week brought trace measurements of 0.01 inch to places like Chinese Camp and Moccasin, Rubin-Oster said. Last Wednesday and Thursday, another system brought 0.04 to 1 inch to Columbia and Sonora.

Mother Lode watersheds have received 8.6 inches of precipitation since Oct. 1, according to a five-station California Data Exchange Center index that includes Calaveras Big Trees and Hetch Hetchy. That’s more than half the annual total of 15.4 inches Calaveras and Tuolumne counties received in 1976-1977, the region’s second-driest water year on record.

Most major reservoirs in and near the Mother Lode were 40 percent to 75 percent full this week, according to a state Department of Water Resources storage summary. On the Mokelumne River, Pardee was 92 percent full and Camanche was 72 percent full.

On the Stanislaus River, Donnell was 41 percent full, Beardsley was 40 percent full and Tulloch was 81 percent full. New Melones, the fourth-largest capacity reservoir in California, was 74 percent full with 1.7 million acre-feet.

In the Tuolumne River watershed, Hetch Hetchy was 70 percent full, Cherry was 77 percent full, and Don Pedro, the state’s sixth-largest reservoir, was holding about 1.4 million acre-feet, 70 percent of its capacity.

One acre-foot of water is about 326,000 gallons, enough to flood a typical American football field 12 inches deep.

Staff with Tuolumne Utilities District, which provides water to about 44,000 Tuolumne County residents, listed Pinecrest at 31 percent of capacity with 5,700 acre-feet. Lyons was 45 percent full with 2,500 acre-feet and Phoenix was 28 percent full with 170 acre-feet.

Contact Guy McCarthy at gmccarthy@uniondemocrat.com or 588-4585. Follow him on Twitter at @GuyMcCarthy.

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