PG&E’s meteorology office in San Francisco is predicting a weakening of this winter’s stubborn La Nina pattern that has helped shunt storms north and kept them from entering much of the state including central California.
John Lindsey, PG&E forecaster from San Luis Obispo says a weakening of La Nina will allow the polar jet stream to drop south and set up a wet pattern when the storm door should be open from late February through early April.
“This ought to provide relief to much of California” suffering this year’s record dry conditions.
“It is a similar pattern to what happened in March 1991,” the so-called March Miracle that helped saved the state after several years of drought. ”I’m not predicting that - but the pattern is the same.”says Lindsey. Like this water year the 1990-91 season was one of driest winters on record at least until a wet March boosted ski resorts, filled reservoirs and saved all water users from catastrophic shortages.
La Niña is characterized by unusually cold ocean temperatures in the eastern equatorial Pacific, as compared to El Niño, which features unusually warm ocean temperatures in the equatorial Pacific. The climate seems to oscillate between the two extremes. ”We don’t know why” admits Lindsey.
With La Nina now weakening equatorial waters are warming - approaching what NOAA calls ENSO neutral conditions likely later this Spring.
La Niña tends to bring nearly opposite effects of El Niño to the United States — wetter than normal conditions across the Pacific Northwest and dryer and warmer than normal conditions over the southern tier including much of California. The impacts of El Niño and La Niña at these latitudes are most clearly seen in wintertime.
Last fall Lindsey wrote that NOAA predicted that the current La Niña would continue to strengthen into this winter. But now it is trending the other way.
The water year 2010-2011 was a La Nina year but California still got doused with substantial storms and above normal precipitation.SLO saw 158% of normal rain. Not so this La Nina year (2011-2012) as the pattern has appeared more as advertised with few storms entering the state but a couple of good ones laying down heavy rain and snow including an early surprise in October.
Little Snow
So far this year many California locations are well behind normal for this time of the year.
In San Luis Obispo city they have received a surprising 12 inches of rain,87% of normal for this time of year (as of 2/6/12).
By contrast the Central Valley city of Visalia has received just 15% of normal says NOAA even though just up the hill at Ash Mountain a few big storms brought the average at this station at the entrance to Sequoia Park to 67% of normal. Nearby Pine Flat Dam has received 62% of normal, Friant 50%, Los Banos 41%,Sacramento 49%, Tahoe 54%,Mt Shasta 61%,Eureka at 88% and Downtown LA is 78% - all before this weeks storm is counted.
It’s the snowpack in the Sierra that worries state Department of Water Resources officials the most - only 33% of normal for this time of the year statewide - just over 6 inches of water content. State officials measuring snow pack talked of walking on grass at high Sierra mountaintops last month.
No snow has pushed at least one Tahoe area ski resort to close pending some good news. Homewood Mountain Resort recently announced it will be closed Mondays through Thursdays “until snow conditions permit full operations or further notice.”
On the Valley floor farmers began irrigating their fields in January and some have run water several times already even as they have seen 70 degree weather - Bakersfield was 81 degrees Monday.
Besides more rain in March, John Lindsey expects cooler temps with the change to wetter conditions as well ending the state’s early season flirtation with sun tans and helping to lower snow levels in the mountains.
Lindsey says PG&E closely monitors weather in part because it helps the utility forecast power and energy needs,prepare for storm events and plan summer hydroelectric supplies.
One good thing- many full reservoirs around the state despite these apparent drought conditions due to last years good performance and the ability to move water around the state.
