As sea surface temperatures and their forecasts continue to rise, so does the level of hype and misinformation about El Niño in general and it's impact on California in particular. To try and give it all a bit of a reality check please see the Misconceptions of El Niño.
In recent days, there have been several media references relating the disastrous 1997 New Year's floods and the January 1982 flooding and mudslides to El Niño. Both of these events occurred the winter before the 1982-83 and 1997-98 El Niño events.
Summer Precipitation AnomaliesDuring Building El Niño Events
There has been much speculation about whether the heavy and prolonged "monsoonal flow" precipitation early this summer into Southwest and the southern Plains has been a characteristic of the building El Niño. Below are the precipitation anomalies for the years where the Oceanic Niño Index was at least +0.5 for the May-Jun-Jul (MJJ) period and it was increasing, along with a composite map of all the years. Based on the composite there does not appear to me an overriding "signal". See http://ggweather.com/enso/summer/summer_precip.htm for individual years.
July 2015 surely defined a mixed climatological bag. Average maximum temperatures ranged from 3.6 degrees above normal (Eureka) to 2.0 below normal at San Jose, while precipitation varied from zero (most places) to 5700% of normal at San Diego!
Even across relatively short distances there were large variations in the average maxima, with San Francisco's anomaly +2.6 and San Jose -2.0, occurring across just 40 miles. Los Angeles and San Diego were likewise juxtaposed with -1.4 and +2.3 respectively. Also interesting were the average minima for the month with everyone being above normal, in a range from +5.2 (Redding) to +1.7 (Fresno).
The huge variations in the rainfall were due to the influx of subtropical moisture, including the remnants of Hurricane Dolores, that produced some locally rain the southern half of the state; and also the very low normals for the month of July.
Just like a sporting event where they go to instant replay to possibly overturn a decision, the same is true with the classification of El Niño's and La Niña's. This has happened with the dataset used to calculate the Oceanic Niño Index (ONI) and consequently the "category" of nearly a dozen El Niño and La Niña events has changed. This was the result of the Extended Reconstructed Sea Surface Temperature (ERSST) dataset being upgraded to ERSSTv4 from ERSSTv3. (See details and previous ONI dataset)
The ONI is a retrospective tool and is used to classify past events, and sometimes the most recent month or two values may shift slightly. It is also not the best indicator in real-time events because it is a 3-month average and may not represent recent dynamic changes very well. For a year to be classified historically as a warm (El Niño) or cool (La El Niña) event there must be at least 5 consecutive over-lapping 3-month periods above/below the +0.5 degrees C criteria.
This updated ONI data and list of events is annotated with an asterisk to show the ones that changed a category. In total 23% of the 3-month periods (from 1950 to present) are cooler by 0.1 deg C, 4% cooler by 0.2 deg C, 1% cooler by 0.3 deg C, 20% warmer by 0.1 deg C, 5% warmer by 0.2 deg C and 47% remaining unchanged. This resulted in 9 events decreasing a category while 2 bumped up a category.
Of most recent interest is that last winter (2014-15) is no longer historically counted as an El Niño year because JFM was adjusted to 0.4 deg C, breaking the string of 5 consecutive periods at or above the 0,5 deg C criteria for a weak El Niño.
Summary of event changes: 2014-15 - no longer El Niño 2008-09 - no longer La Niña 2005-06 - no longer La Niña 1999-00 - from strong to moderate El Niño 1994-95 - from moderate to weak El Niño 1987-88 - from strong to moderate El Niño 1979-80 - increased to weak El Niño 1968-69 - from moderate to weak El Niño 1967-68 - increased to weak La Niña 1956-57 - no longer La Niña 1951-52 - from moderate to weak El Niño
There are now a total of 23 El Niño events since 1950; with 12 being "weak", 6 being "moderate", 3 "strong" and 2 "very strong". Of the cool La Niña events, there is a total of 20; with 11 in the "weak" category, 5 "moderate" and 4 "strong".
The latest El Niño "plume forecast" for was released yesterday and it showed an even stronger event for the upcoming winter and fall. The mean forecast value of the 16 dynamic models peak at a "very strong" ONI value of 2.2 for the Oct-Nov-Dec (OND) period and then cools to 1.9 in DJF.
The average of the dynamic models has continued to get stronger with each successive model run.
Comparing the very strong El Niño event of 1997-98 with 2015 observed so far and the forecast.
These are the SST anomalies for July 15, 1997 and July 15, 2015. The two big differences are the strength of the 1997 equatorial signal (stronger) and then the 2015 "warm blob" in the Gulf of Alaska being warmer the the positive anomaly of 1997.
The weekly SST values so far in 2015 compared to 1997, plus the forecast for the remainder of the year.
Warm California Coastal Waters Not Necessarily El Niño Related
In recent days there have been numerous reports of warmer than normal water along the California coast as well as an abundance of sharks, red crabs and dead marine life washing ashore. And in too many reports there has been at least an implied linkage to El Niño. But the warmer than normal water associated with El Niño occurs in the tropical Pacific, about 2500 miles southwest of California. Historically, the waters along the northern and central California coast have been above normal during only about half (55%) of the El Niño events since 1950, and 64% of the times in the Southern California coastal waters. (See #7 at http://ggweather.com/enso/enso_myths.htm )
It should also be noted that California coast waters were also well above normal last summer, long before the formation of the current El Niño. This warming is more likely associated with the "warm blob" in the northeast Pacific, which is likely a byproduct of the persistent ridging off the west coast that has been the prime factor in the ongoing drought.
To view historic Sea Surface Temperature (SST) anomalies worldwide see http://ggweather.com/sst.htm. The clickable map is for the north Pacific but there is data for the entire globe via a pulldown menu. The data can also be displayed as a time series. Thanks to Scott Archer of IPS Meteostar for his programming wizardry in helping make this data so easily accessible.
Today is the last day of the California rainfall season (July 1 to June 30) and as expected it was another dry year. Most of northern California was between about 70% and 80% of normal, with central California having a wider range between 55% and 80%, and southern California mostly between 50% and 60%. There were a few outliers in each category, primarily boosted by singular convective events.
The important Sierra Nevada precipitation indices were equally low with 71% in the northern Sierra Nevada and less than 45% of normal in central and southern Sierra. See http://ggweather.com/ca2014rain.htm.
These tables and chart show the total deficit in California rainfall since the 2011-2012 season July 1 to June 30) in both inches and percent of normal.
For example, San Francisco is 31.63 inches behind their normal four-year total. Consequently, to make up all of the deficit, the rainfall that San Francisco would need this coming season would be 55.28" (i.e., 31.63" + 23.65") or 234% of normal. [The all time record for San Francisco is 49.27"!!]
It should be noted that making up the rainfall deficit is very different than the requirements to "end the drought" as the components of a drought are dependent upon a myriad of variables like the type of user, population, existing supplies etc.
The current mean of the 17 dynamic forecast models is 1.8 in the October-November-December period, but in looking at the individual members that make up the mean, there are seven of the models that exceed 2.0, including the Japanese model (2.7), NASA (2.5) and both NOAA and ECMWF at 2.4.
I have searched high and low but I can't find anything that defines a single hot day as a "Heatwave". Yet headlines and breathless newscasters have insisted on calling this past Monday and now the warm-up expected tomorrow "heatwaves".
Climatologically, this type of weather is to be expected. For example, Livermore averages two 100-degree maximum days in June while San Jose averages four 90-degree days. It is occasions when there are multiple consecutive days that are a these levels (and minimums remain abnormally high overnight) that really constitute a "heatwave"
Here are a couple definitions of heatwave: - World Meteorological Organization: "...when the daily maximum temperature of more than five consecutive days exceeds the average maximum temperature by 5 °C..."
- National Weather Service Glossary: A period of abnormally and uncomfortably hot and unusually humid weather. Typically a heat wave lasts two or more days.
That being said, it is always advisable for persons to take precautions to protect themselves and others when there is abnormally hot weather, especially early in the year when most are not acclimated.