31 May 2015
Will El Nino Break the California Drought? The Odds Are Not Good
Posted by Dan Satterfield
I‘ve been doing a little research into the coming El Nino and how it might relieve the epic California drought. The news isn’t very good, but the short of it is this: California needs to beseech Mother Nature for a supersized El Nino, because a regular size will probably not do the job. Look at the image above from a blog post by Tom DiLiberto last fall (on the excellent site Climate.Gov). It was thought that we might see an El Nino last winter, but while it came on strong, it fizzled quickly in the autumn. This year however, it looks like we really do have an El Nino on the way, (although the forecast skill in spring is lousy) and there are signs it may be a strong one.
In the graph that Tom posted (above) you can see that El Nino years (orange dots) were sometimes wet and sometimes dry, while the La Nina years do show a pronounced dry signal. This means that hearing El Nino and immediately thinking California flood is dead wrong. That said, Meteorologist Jan Null, points out that if you look at just the strongest El Nino’s, the signal for a wet winter IS strong, with 4 out of 5 bringing a wet winter and above normal rainfall to California. The 1982-83, and 1997-98 El Nino’s being good examples of this.
Any decent meteorologist will immediately point out that EVERY El Nino is different, and as I mentioned earlier this week, the warm waters off the coast of California, may very well make this one unique, even if it is strong. That warm water (above normal, you’ll still need a wetsuit if you want to surf the Golden Gate) has likely played a major role in the California drought, and it seems to be showing little signs of cooling. It may actually be expanding as THIS ANIMATION from NCEP shows.
The latest ENSO advisory from NOAA’s Climate Prediction Center has an analysis that may be very telling. It takes this week’s temperature anomalies and subtracts them from those in April. Notice the warming water off the coast of Equatorial South America, a sign of a growing El Nino, but also notice that the waters off California have either stayed the same or warmed some.
The latest El Nino forecast models all show an El Nino coming but some models are showing a strong one and others showing a moderate event, and remember that California needs a biggy to have high odds on a wet winter. Also remember that El Nino forecasts this far out have little skill. Spring El Nino forecasts are especially poor, and more on that from Michelle L’Heureux, again at the excellent ENSO Blog at climate.gov.
There is some more bad news for California, based on the latest atmospheric and ocean temperature patterns, and Meteorologist Pete Parsons at the Oregon Dept. of Agriculture talks about it here. Finding patterns that look similar to past El Nino’s/winter/summers etc. is a good way to make a long-range forecast, and this technique is used widely in making the long-range forecasts for the hurricane season, winter etc. (except by the Farmers Almanac, where they just guess and a gullible American public buys 500,000 copies each fall, so why would they ever stop!).
Parsons finds that the best analog years are 1977,1980, and 2005, but only 1977 managed to be a decent El Nino and it was still quite weak. That likely will not do for California, remember the odds say they need a big one. His methods for this are outlined here, but If you look at the SST Anomalies (Maps below) in May 1997 (Just before a BIG El Nino) and this May, you can see some remarkable similarities. Perhaps 1997 is about to become an analog to this year. That would be very good news for California since the 1997-98 El Nino was the second biggest ever, after 1982-83, and was a very wet winter. Now, remember every El nino is different but if you are wondering what the winter of 1997-98 was like… try this.
Before you west coast folks do any “California Dreaming” of a snow pack of 60 feet in the Sierra, let me just mention that no matter what, you are still overdue for the BIG ONE. Especially Southern California. Check out the Third Uniform California Earthquake Rupture Forecast (Oh how I LOVE that name).
Have a nice day, and let’s do lunch soon!