Sierra snowpack below average after dry month
January 29, 2013
Almost every year since 1987, Chief of the California Cooperative Snow Survey Frank Gehrke has recorded a mid-winter lull during which fewer storms hit the Sierra Nevada. And 2013 was no exception.
The water content at Phillips Station near Echo Summit was 12.7 inches Tuesday, or 66 percent of the long-term average. When Gehrke conducted the year’s first survey at the start of the month, water content was at 101 percent of average.
Statewide, the snowpack water content was 93 percent of average for the date and 55 percent of the April 1 measurement –typically the snowpack’s peak.
“Unfortunately as we foresaw, we had very little storm activity in January. The storage in the reservoirs is the bright spot, but that’s not to say the snowpack can’t come back. It’s just not as optimistic as before,” Gehrke said.
Gehrke said the Northern Sierra Nevada typically experience a mid-winter lull in storm activity that for the past few years has come in January. High-pressure centers build up just off the coast and then act as a barrier that prevents winter storms from moving inland toward California.
Instead, the storms get rerouted toward the Pacific Northwest or Alaska. Those systems can even affect the Midwest or the East Coast if they detour to the north.
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“The duration of the lull is the difference between a good water year and a so-so water year. We typically get water during discrete, intense events. We have storms that come through and dump a bunch of snow,” Gehrke said.
SNOTEL data collected over the last decade from the Natural Resources Conservation Service shows that snowpack water content tends to flatline for about two to six weeks in January or early February before rising gradually through March or the start of April. While the length and severity of the lull varies, each year since 2004 saw a period of little or no snow.
Meteorologists can’t predict how long the high-pressure centers will blockade the coast, nor do they know exactly why they form during the winter, Gehrke said. It’s probably linked to long-term ocean patterns like the ones that cause El Nino and La Nina, but there isn’t enough data yet to piece together the details, he said.
None of those massive winter storms that skiers and riders dream about have moved through the region recently. Unless the South Shore gets what Gehrke calls a “miracle March” or another series of powerful storms, snowpack water content will be about what it was last spring, he said.
The forecast isn’t entirely negative though. Gehrke said those high-pressure centers seem to be dissipating and important water-storage reservoirs are above average thanks to precipitation in November and December. Lake Oroville is at 113 percent of average for the date and Lake Shasta is at 111 percent of average, according to a Department of Water Resources press release.
The DWR estimates that it will deliver 40 percent of the requested water this year to supply 25 million individuals and almost 1 million acres of irrigated farmland. The snowpack normally provides about one third of the water for California.
“Those early-season storms also erased the deficit in our reservoir storage, but relatively dry weather this month is once again a reminder that the weather is unpredictable and we must always practice conservation,” DWR Director Mark Cowin said in the release.