Depending on how far south a weak weather system tracks over the Central Sierra, it may rain Thursday in Sonora, Columbia and Twain Harte, and light snow may fall at Sonora Pass Wednesday and Thursday.

“We have a very large low pressure system sitting over the western United States, and we have this weak impulse moving over California sliding down from Oregon and Washington,” Hannah Chandler, a meteorologist with the National Weather Service in Sacramento, said before 1 p.m. Wednesday in a phone interview. “That’s bringing chances of rain and light snow at higher elevations.”

That wet, cool storm a week ago brought eight-tenths of one inch of rain and snow to Mother Lode watersheds that include Calaveras Big Trees and the Stanislaus River, and Hetch Hetchy and the Tuolumne River. That is 119 percent of normal for the date Oct. 10 in the new water year that started Oct. 1.

National Weather Service data shows that since Oct. 1 Sonora has received 0.48 inch and Groveland has received 0.63 inch of precipitation, Hannah said.

Forecasters are qualifying their predictions for this weak system with medium confidence. They say less than one inch of snow is possible Wednesday and Thursday at Carson Pass on Highway 88, Ebbetts Pass on Highway 4, Sonora Pass on Highway 108, and other isolated areas above 8,000 feet elevation.

Up at 9,624-foot Sonora Pass, the second-highest paved route over the Sierra Nevada, below-freezing overnight lows in the 20s are expected Wednesday night and Thursday night.

Drying winds coming with the weather system could gust 10 to 15 miles per hour in the Mother Lode foothills and 20 to 25 miles per hour at high elevations including Yosemite National Park. Breezy winds are expected to couple with lowering humidity levels and increase fire weather concerns through Friday.

San Andreas and Angels Camp can expect sunny weather with daytime highs in the 80s through at least Saturday. Twain Harte and Mi-Wuk Village can expect daytime highs in the high 60s to low 70s this weekend.

As of Wednesday afternoon, all major roads in Yosemite National Park, including Highway 120 and 9,945-foot Tioga Pass, the highest paved route over the Sierra Nevada, were open with no restrictions.

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

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