The following excerpts on the drought situation in California come from a recent post by Daniel Swain from WeatherWest.com.
To view the article in its entirety click on the article title below.
by Daniel Swain on August 31, 2014.
The weather in California has been relatively uneventful over the past few weeks. Periodic thunderstorm activity has continued to affect mainly inland desert and mountain areas, mostly in the southern part of the state.
Drought update
I’ll keep this short: California’s still experiencing extreme, record-breaking drought conditions. Impacts continue to become more widely felt–and have recently started receiving considerably more media attention. Reservoir levels are still dropping rapidly, and will continue to do so for at least another 2-3 months.
While nearly all major reservoirs are still above the record-low levels set during the 1976-1977 and 1987-1992 droughts (largely due to water management decisions made this year), a number of reservoirs stand a good chance of dropping below these previous record lows during October/November 2014. The Drought Monitor, unsurprisingly, continues to suggest that a very large fraction of California is experiencing exceptional drought–the most intense categorization.
An update on El Niño
Reports of El Niño’s demise have been…greatly exaggerated. While Niño region sea surface temperatures (SSTs) did decrease notably in the wake of the big Kelvin wave earlier this year, they’re on the increase once again. A new Kelvin wave is currently propagating across the Pacific, and is expected to arrive along the shores of South America in a few weeks.
This wave is not nearly as strong as the one earlier this year, but it should be enough to formally establish El Niño-like SST anomalies by the fall months. Nearly all major dynamical and statistical model guidance still suggests the likely development of El Niño conditions by the fall, though a strong event now appears to be unlikely (most likely: weak to moderate strength). This does have implications for conditions in California, since historically only strong El Niños have consistently been linked to above-normal precipitation in the state (this is especially in the north, where much of the water storage capacity resides). Thus, it does not currently appear that a strong El Niño will bring drought relief to California this winter. On the other hand, as I’ll discuss further below, this does not necessarily mean that California is in for a dry winter.
What can we say about the coming winter? Is drought relief on the horizon?
As I noted above: a strong El Niño–which might have been a meaningful predictor for a wet winter to come–now appears very unlikely. But why, exactly, is El Niño so important in the first place? As I’ve previously discussed, El Niño affects California weather in several direct and indirect ways, but the primary mechanism during the cool season arises from the re-arrangement of SSTs in the Pacific Oceans and subsequent effects upon the storm track. Because it’s the spatial patterns of ocean temperatures–the actual distribution of warm vs. cool conditions–which can affect large-scale atmospheric conditions by reorganizing atmospheric temperature differences.
Most models do have modest skill during the “core” wet months, though, from January through March. None of the major dynamical models are currently projecting a wet fall, so it appears that the likeliest outcome for the early part of the rainy season is near or below average precipitation. Later this winter, however, all bets are off. Some of the most skillful dynamical models have been hinting at the possibility of a rather wet period during January and February.
What’s the overall message here? Right now, there aren’t any clear precipitation signals for the upcoming winter. However, it does appear that near or below-average precipitation is the most likely outcome for the fall months, while there are nearly equal chances of above or below normal precipitation later this winter. Because there is no obvious drought relief on the horizon, it would be wise to prepare for another dry year. Stay tuned.
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