Wet, wacky spring one for the record books
San Luis Obispo Tribune
Published: Sunday, Jun. 12, 2011
The weather this spring has been an anomaly. Rain and snow in California this June, historic floods along the Mississippi River, blistering heat waves and monster tornado outbreaks east of the Rockies have made this season one for the record books.
On Tuesday, the temperature reached 103 degrees at Minneapolis-St. Paul International Airport. This shattered the old record of 95 degrees set in 2004. Flooding on the Mississippi River reached levels not seen since 1927, with thousands of acres of farmland still underwater. Tornadoes have killed hundreds this spring, with Missouri and North Carolina especially hard hit.
Last weekend, 1.05 inches of rain fell at Cal Poly, where official records for San Luis Obispo are kept. That breaks the previous rainfall record total of .80, set in June of 1991. Rocky Butte near San Simeon recorded nearly 4 inches of rain last weekend!
At the same time, significant snowfall accumulations were recorded in the higher elevations of the Sierra. This year's snowpack was one of the deepest on record.
"In my past 40 years as a hydrologist for Pacific Gas and Electric Company, this snowpack is the largest for this late spring date that I can recall," Gary Freeman said. "It wasn't the largest snowpack in terms of water content on record. Eight years, including 1995, 1983, 1969, 1958, 1952, 1938, 1916, and 1914, were all larger in the Central Sierra as measured at the Donner Summit snowcourse during the past 100 years. But it is the largest on record for this time of year."
In a normal winter, most of the snowpack melts in May.
The Stouts Meadow automated snow sensor site at 5,400 feet, above McCloud Reservoir, has exceeded the 1998 mark, a record snowpack with a late melt.
"The snow is thick in the higher elevations," Freeman said.
Should the temperatures suddenly warm up — and, at this time of the year, temperatures can turn on a dime — melting snow in the Sierra could flow down from the mountains all at once, causing flooding.
The largest concern statewide focuses on the San Joaquin River. Reservoirs such as Exchequer and Millerton continue to be managed with space left to help accommodate the expected deluge of spring runoff.
Many readers have asked me what is causing this wacky weather. Is the recent weather an anomaly or a sign of things to come with a warming climate?
Perhaps it's the residual effects of La Niña and the negative phase of the Pacific Decadal Oscillation, a long-lived El Niño-like pattern. Add a touch of Maiden Julian Oscillation, and a lot of remaining unknowns, and we have this year's delayed snowmelt.
This year's La Niña was one of the strongest in the past half-century, and seawater temperatures along our coastline seem to support this, averaging nearly two degrees Fahrenheit below average at the Diablo Canyon power plant, for instance.
However, we still don't understand what causes the areas of high pressure to switch from one part of equatorial Pacific to the other, producing the El Niño/Southern Oscillation, or ENSO, cycle.
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