What happened to the rain?
Less than a year after the drought was declared over, precipitation has been relatively scarce in the Sacramento area and Northern California so far this season. This week’s cold snap is accompanied by a round of dry weather that’s expected to last at least another 10 days.
It’s too soon to panic about a prolonged dry spell, however.
The National Weather Service said precipitation this season is actually running slightly ahead of schedule in the northern Sierra Nevada, thanks to a wetter-than-average November. But the weather gauges are emptier the further south you go, and rainfall truly has been in comparatively short supply in practically every California city.
Sacramento’s rainfall is just 68 percent of average for the season, according to Department of Water Resources data. Rainfall in Stockton is just 33 percent of average, and the precipitation in Southern California, which is battling a series of wildfires, has been practically nonexistent.
Michelle Mead, the weather service’s warning coordination meteorologist in Sacramento, said the weather probably seems a lot drier than usual because most Californians are still recalling last winter’s endless rains, which broke the five-year drought and produced the wettest winter in Northern California’s recorded history.
“We aren’t doing that terribly bad as far as Northern California is concerned,” Mead said. “In the grand scheme of things, we are doing sort of OK.”
This week’s forecast is all about extreme temperatures, not atmospheric rivers. The weather service said Sacramento Valley temperatures would approach freezing Tuesday night, with Sacramento expecting 34 degrees, and Modesto hitting 35 degrees. Santa Rosa was in line for a low of 29. Farmers were warned about potential damage to crops and livestock.
Although the official “water year” in California begins Oct. 1, the bulk of the precipitation falls between Dec. 1 and the end of February. In the short term, a ridge of high pressure is keeping rain from reaching the West Coast at least through mid-December, although Mead said it’s hard to say what the rest of the season will bring.
While rainfall is important, an abundant snowpack is critical; it can act as a second set of reservoirs and in most years can hold 30 percent to 40 percent of the state’s water supply.
Frank Gehrke, who runs the closely-watched snow survey program at the Department of Water Resources, said snow levels so far appear to be running below last year’s accumulations. But the results are somewhat “scattered” and it’s too soon to make predictions about the rest of the season, he added.
“There’s snow up there; it’s still early in the season,” he said. “Right now we’re sitting, looking at blue skies but it can turn around very quickly.”
Climatologists have become increasingly concerned about the Sierra snowpack’s long-term viability, saying climate change is expected to turn a significant portion of the snow into rain, making it more difficult to capture and store for human use and raising flood risks.
A new study led by the Desert Research Institute, a Reno think tank, said the snow line in the northern Sierra has crept up about 1,200 feet in the past decade. The study was published last month in Water, a scientific journal.