La Niña is weakening, but don’t hold your breath for a “March miracle”
This image shows La Niña conditions from last month, collected by NASA's Jason-2 satellite.
This has been a historically dry winter, dry enough that it’s likely to land a spot as one of the top ten driest since the Gold Rush. And even though La Niña is waning, that probably won’t make much of a difference, because there’s a delay between when ocean surface temperatures change, and when that change actually has an effect on our weather.
“March 20 is just around the corner, and that’s the first day of spring. Our winter — our snowpack and our rain — is essentially over,” NASA Jet Propulsion Laboratory climatologist Bill Patzert told me. Though Patzert’s observation comes as three Pacific storms are poised to potentially bring a week of rain to Northern California, he said, “a weakening La Niña won’t necessarily give us a March miracle in terms of snowpack and rainfall.”
La Niña is caused by colder-than-average ocean surface temperatures in the equatorial Pacific. It typically makes for warm, dry winters in California. But not always. Last year was also affected by La Niña, and it was historically wet.
Precipitation outlook for winter 2011-12, showing the likelihood of below average precipitation in Texas and other drought-stricken states.
Does this mean Texas is toast?
By Michael D. Lemonick
As most Californians know, El Niño is a periodic unusual warming of the surface water in the eastern and central tropical Pacific Ocean. Actually, that’s pretty much a lie. Most people don’t know the definition of El Niño or its mirror image, La Niña, and truthfully, most people don’t much care.
What you do care about if you’re a Texan suffering through the worst one-year drought on record, or a New Yorker who had to dig out from massive snowstorms last winter (tied in part to La Niña), or a Californian who has ever had to deal with the torrential rains that trigger catastrophic mudslides (linked to El Niño), is that these natural climate cycles can elevate the odds of natural disasters where you live. Continue reading
Frank Gehrke conducting last year's first snow survey of the season. (Photo: Gretchen Weber)
All the wet weather that’s been drenching much of the state has left the Sierra Nevada with an extra-thick blanket of snow, which has water officials optimistic about the state’s water supply for 2011.
Using a combination of manual and electronic measurements, the state’s Department of Water Resources conducted its first snow survey of the season on Tuesday, and found the water content of the state’s snowpack at 198% of normal for this time of year. Last year at this time, the statewide average was just 85% of normal.
Pacific ocean conditions that often portend a dry winter sure haven’t so far.
Scientists like to joke that “climate is what you expect, weather is what you get.” The relatively soggy winter so far is a classic example of that.
Satellite image from last weekend, showing storm systems marching across the Pacific toward California. (Image: NASA)
A closely-watched oscillation in the Pacific is in the La Niña phase this winter, creating colder-than-normal surface temperatures and distorting weather patterns. Usually a La Niña means drier-than-normal conditions for Southern California in particular and often for northern parts of the state as well. Not this year–at least not so far. The rain set multiple records over the weekend. Los Angeles has had a third of its average annual rainfall in a week. So what’s going on? Continue reading
Answer: Both. It depends on your historical time frame.
With a global average surface temperature of 79 degrees Fahrenheit, 2008 was the coolest year since 2000, according to climatologists at the NASA Goddard Institute for Space Studies (GISS). But it’s also the ninth-warmest year since 1880, so it’s probably not time to invest in a ski resort just yet.
Including the 2008 dip, the 10 warmest years on record (since 1880) have all occurred between 1997 and 2008, according to NASA.
The NASA scientists attribute 2008′s relatively lower temperature to a cooler Pacific Ocean, due to a strong La Nina pattern in the first half of 2008. La Nina and El Nino are opposite phases of a natural oscillation of upwelling and subsequent temperatures in the equatorial Pacific Ocean.
2008 temperatures in the United States were cooler than any other year this decade, but, as illustrated on the map below, other parts of the world such as Eurasia and the Arctic were exceptionally warm.
Director of GISS James Hansen predicts that because a shift to El Nino is expected to start this year or next, it “still seems likely” that we’ll see a new record high for the average global surface air temperature in that time frame.
At the annual “Watershed Event” fundraiser for the Sacramento River Watershed Program, Elissa Lynn, Sr. Meteorologist for the state Dept. of Water Resources, offered a rundown of where we stand at the start of the official “water season.”
The short version: It’s bleak.
As I noted last week, Lake Oroville, a key reservoir on the Feather River, stood at 31% of capacity as of midnight on September 30. Readings from the same hour showed the state’s largest reservoir, Shasta Lake, at 30%; Folsom Lake (American River, east of Sacramento) at 28%; and San Luis Reservoir, east of Silicon Valley at 12–yes, twelve percent of capacity.
Capacity figures by themselves can be misleading. We expect reservoirs to be low this time of year, right at the end of the dry season. But as DWR was taking these readings, Oroville, to use one example, was at 49%–less than half–of “normal” for this time of year.
So, much depends on the coming winter. Even with all the advanced tools that forecasters have at their disposal in this first decade of the 21st Century, it’s hard to say how much water we’ll wring out of the skies this winter. Lynn says we’re in a “La Nada” pattern, meaning the Pacific Ocean isn’t giving a strong signal for either El Nino or its opposite, La Nina. The two conditions describe the degree–or lack–of cold water upwelling from the ocean depths, which has a strong influence on California’s precipitation patterns.
But Lynn says the consensus among forecasters is “leaning toward a dry-to-average” winter and average won’t get us there. We’ll need several soggy months to make up for lost water and avoid more severe water restrictions throughout the state next summer.