This post contains a portion of a well-worth-reading blog item written by Deke Arndt, who is Chief, Climate Monitoring Branch, of the NOAA National Centers for Environmental Information (NCEI) in Asheville, North Carolina. The blog posting is titled "Why El Nino Is Like A Bad Bartender". His post has some very useful information on the scenario for possible winter precipitation in the western U.S. drought areas in 2015-16.
By Deke Arndt
Let’s say you have a favorite establishment, where everybody knows your name, and they bring you “your” beverage on sight. And then one night you go in, and based upon your past experience, you sorta expect the bartender to bring you your favorite beer. Instead, maybe he unexpectedly brings you a warmer-than-normal beer, or even (shudder) a wine cooler. El Nino is like that bartender. Seeing him when you walk in may tilt your odds toward getting your favorite beer, but it’s not a guarantee. In other words, sometimes El Nino is the bartender who doesn’t bring you what you ordered.
El Nino is important, so we appropriately pay attention to it when considering seasonal outcomes. However, El Nino is not the only game in town, and just like external factors may distract your bartender, each El Nino is born into a unique global situation, so its push on seasonal outcomes is unique as well. Indeed, this year, we have "the “Blob,” reduced Arctic sea ice, and a persistent North Atlantic feature that weren’t in play in the 20th-century El Ninos of yore.
Let’s look at some historical precipitation outcomes for the cold season (October through March) for each year since 1950. Why cold season? Because it’s starting now, and it is also when much of the West gets the lion’s share of its precipitation. It’s also more responsive to El Nino’s influence, compared to other months on the calendar. Why 1950? That coincides with the beginning of the Oceanic Nino Index era, which was a factor in selecting historic El Ninos.
California isn’t the only drought-stricken state, but it draws upon water resources from throughout the West. In terms of water—in some ways, at least—California goes, so goes the West; as the West goes, so goes California.
First of all, the average outcome is fairly optimistic: during strong El Nino years, precipitation is around six inches above the long-term average. However, two of those six strong El Ninos actually delivered below-average precipitation. So, a strong El Nino doesn’t guarantee a wet outcome for California statewide, even though it significantly pushes the odds towards wet conditions.
This situation is magnified in Northern California. Drilling down--in Northeastern California, there is a modestly wet average of all six strong El Ninos, but it comes as a result of one whopper episode (1982-83), three near-average episodes, and two below-average (dry) episodes.
On the flip side, southern California has had a much more consistently wet relationship with strong El Ninos. This is best shown in Southern Coastal California, where each of the six strong El Ninos have delivered at least nominally above-average precipitation, and five of them have come in notably above the norm. As such, the current winter outlook from the Climate Prediction Center (CPC) indicates the highest probabilities for increased precipitation are across southern California.
Persistent drought and wildfire have been year-long issues in the Northern Rockies. How might El Nino play out here? Unfortunately, the influence of a strong El Nino to the region is a drying one. Western Montana outcomes are almost the mirror image of Southern California: all of them at least nominally drier-than-average, and most of them seriously so.
El Nino can play a huge role in seasonal outcomes. It’s no coincidence that, for much of the country, the current seasonal outlook looks a lot like the pattern of average El Nino outcomes. However, as forecasters can tell you, those average outcomes can be pulled apart into specific examples which may sometimes stray from the averages. Some places have a pretty consistent response, and for these areas, confidence in outcomes is higher. In other places, the signal is anything but consistent. For our friends in northwest Wyoming, both the wettest and the driest cold seasons on record came during strong El Nino episodes.
One more point: the Western drought is entrenched. It took years to get into the current situation; it will take more than one wet season to get out of it. Let’s hope that we put a big dent in the drought this year, but one season, and probably even one El Nino, is not a single magic bullet.
The full article is at this link: https://goo.gl/…
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