Ski resorts are crowing over a major snowstorm that began pounding the Sierra Nevada late Thursday, with forecasters warning of white-out conditions, road closures and up to five feet of new snow at the highest elevations by Saturday morning.
After a dismally dry start to California’s winter, some observers have even gone so far as to tout this month’s bounty of storms as reminiscent of the “March Miracle,” the famous, stormy March 1991 that launched the beginning of the end of the state’s stubborn 1987-1992 drought.
But is this March another miracle? Not yet, say experts.
Every storm helps improve the state’s summer water picture, scientists and state water planners said Thursday. But even taking into account this storm and a big one two weeks ago, the Sierra Nevada snow pack — the source of nearly one-third of California’s water supply — still is only about half of normal for this winter season, with this month’s totals measuring just half of the 1991 miracle month’s final tally.
In other words, California still needs lots more snow.
“We’re definitely better off than we were at the end of February,” said Gonzalo Cortés, a scientist at UCLA’s Civil and Environmental Engineering Department who specializes in studying snow trends. “Back then, we were worse than in 2015, the worst year of the drought. But in terms of comparing us to 1991, we have a long way to go still.”
The math is fairly simple. California water experts measure snow pack not so much for the depth of the snow, but for the amount of water it contains. That’s because as the snow melts in spring and summer, it flows into reservoirs and is delivered to farms and cities during the rest of the year.
Dense, wet snow has more water in it than light, fluffy snow. So when researchers or weather forecasters on TV talk about the snow pack, they’re really talking about the “snow water content,” or the amount of water that would come out of the Sierra snow if it were all melted at once.
The Sierra Nevada snow pack increased from an alarmingly low 19 percent of normal three weeks ago to 40 percent of normal on Wednesday. That’s a jump from about 4.6 inches of total water content up to 10.9 inches. The historic average for April 1, however, is 30 inches.
The storms blanketing the mountains now will help get California closer to that historic average, bringing in about another 3 inches of water content, the National Weather Service estimates. That should move the seasonal total to about 14 or 15 inches, or about 50 percent of the historic average for this time of year. That’s still just half of normal.
“These storms are really helping and are positive. We’ll take as much as we can get in the next two weeks,” said Dave Rizzardo, chief of snow surveys and water supply forecasting for the state Department of Water Resources. “Overall it’s turning wet, but it’s been a dry winter. It’s realistic to think we could end the season with 60 to 70 percent of normal.”
Luckily, last winter’s monster storms, which ended the five-year drought, filled many of California’s reservoirs.
“By all standards we’re looking at a below-average year,” Rizzardo said, “but the reservoirs are in good shape, so water supply-wise, I think we’re OK.”
