Spring is officially here and has ushered in what forecasters are calling an atmospheric river storm to continue a moist March that is so far helping balance out a drier than normal winter season.

Equinox happens twice a year when the sun crosses the plane of the equator and night and day are about equal length all around the world.

Vernal equinox in the northern hemisphere happened at 9:15 a.m. Tuesday, so by this morning we will be in the second day of spring, according to global timekeepers.

Here in Calaveras and Tuolumne counties, spring-like weather has already sprung a couple times since New Years Day, including warm spells in January and a February heat wave.

The current atmospheric river storm is carrying tons of moisture, and it’s coming out of the Gulf of Alaska. The heaviest rains and snow are expected Wednesday and Thursday, with continuing chances of showers Friday and Saturday.

Depending on how far south this weather system tracks as it moves over the Central Sierra, places like Sonora could get 3 to 4 inches of rain by early Saturday, and Yosemite Valley could get 5 to 7.5 inches.

At higher elevations like Arnold, Twain Harte and Buck Meadows, there’s a winter storm watch in effect from 11 p.m. today to 11 p.m. Thursday. Snow levels are expected to remain above major pass levels through early today, and then lower by tonight, with heavy snow possible above 6,500 feet.

Gusting winds today and Thursday are expected under 20 miles per hour in the Sonora area and 20 to 30 mph at higher elevations like Yosemite. Thursday into Friday, snow levels could come down as low as 2,500 feet elevations. Ebbetts, Sonora and Tioga passes could all get up to 4 feet of new snow by Saturday.

The first day of this multi-day system brought gray skies to the Mother Lode but very little rain. In 24 hours preceding 5 p.m. Tuesday, a smattering of drizzle fell on the Mother Lode.

Nearly half the current water year’s precipitation in the Central Sierra has come in March. A five-station index for major Mother Lode watersheds including the Stanislaus and Tuolumne show 19.1 inches since this water year started Oct. 1, and about 9 inches of that total has come in the past three weeks, boosting the total to 62 percent of average for the date March 20.

In spite of recent wet, cold storms, most of Tuolumne County remains in moderate drought and all of Calaveras County remains abnormally dry, according to scientists with the U.S. Drought Monitor.

A brief break in the weather is expected Friday, followed by chances of showers Friday night and Saturday.

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