An El Niño For California!

Last year, climatologists were warning us that we could have
one of the biggest El Niños in history, perhaps one even rivaling the legendary
El Niño of 1997-1998. Those forecasts never verified, but you wouldn’t know
that by our weather this past winter. El Niño winters are generally warmer
and drier than normal in the Pacific Northwest, and boy oh boy were we warm.
While we had near-normal rainfall, most of this rainfall occurred in short,
heavy spurts due to warm, subtropical systems soaking the area. All of this
made for, as I’m sure you are well aware, a less-than-optimal ski season.

The above picture shows pictures of Folsom Lake, a reservoir
25 miles northeast of Sacramento in Northern California. The picture on the
left is from July 2011, and the picture on the right is from January 2014.
During July 2011, the reservoir was at 97% total capacity and had 130% of its
average capacity for that date. For January 2014, the reservoir was at 17%
total capacity and had 35% of its average capacity for that date. I can’t even
tell if the reservoir reaches the dam in the foreground. The lack of water in
California is frightening. Jerry Brown, the governor of California, has called
for a 25% reduction of water usage in 2015 compared to 2013 levels, and
numerous measures are being put in place to ration water. The latest, a
“tiered” measure where the more water you use, the more you would pay
per gallon, was recently ruled unconstitutional this past Monday. 

This is the kind of stuff that drives me crazy. There seems
to be a common theme in American society of being unable to take action on a
pressing environmental issue because it will violate some peoples’ rights. When
a situation gets really, really serious, taking swift action is more important
than finding a perfect solution. What’s more important… having people who use
large amounts of water pay unfair sums of money for using it (while farmers get
off for free and Nestle (Arrowhead) illegally pumps their water from California’s
national forests and sells it to drought-free states for a profit), or
continuing to watch California’s water supply dwindle? In my opinion, when
there is a crisis, it is more important to get an imperfect solution in place
that can be edited later than take no action at all. The lack of urgency
towards mitigating environmental crises in politics confounds me. But that is a
topic for a different blog.

So if California won’t help themselves, will Mother Nature
come to the rescue? I am cautiously optimistic that she will. But before we
discuss how the current El Niño will unfold, let’s take a look at the
effects of past ones for the continental U.S. I hope you like pictures. 🙂

During El Niño years, the jet stream that comes off the
Pacific and brings us our big storms tends to shift to the south. As a result,
we tend to be warmer and drier, while California tends to be cooler and wetter.
This pattern is not unique to the West Coast; during El Niño years, the
entire northern and southern tiers of the U.S. follow a similar trend.

The maps below show the composite precipitation and
temperature anomalies during El Niño years over the states. Of particular
note is the sharp gradient in precipitation between the Cascades and the Sierra
Nevada. With warmer and drier-than-normal conditions, the
Cascades are often starved of snowfall, while the Sierra Nevada get absolutely
crushed.

Now that we’ve got that covered, we’re ready to take a look
at El Niño’s current status. But before we do that, let’s quickly review
our El Niño “regions.”

El Niño occurs in the tropical Pacific, and there are
different Niño “regions” that are used as an indicator of El Niño
strength. They are all important, but Niño 3.4 is the one that is generally the
most representative of an El Niño event. The graphs and maps below show the
temperature anomalies in these regions over time. All of the pictures below
were retrieved from the Climate Prediction Center’s latest El Niño/Southern Oscillation (ENSO) diagnostic discussion.

As you can see, sea-surface-temperatures (SST) were above
average for the entire winter, but for the tropical Pacific to be in an El Niño
state, the SST must have a 3-month average of at least 0.5 °C above
normal. We barely, barely made El Niño criteria this past winter, but as you
can see, all of the Niño regions are warming rapidly, and we are now solidly in
weak El Niño conditions.

Warming is also very apparent at depth, as the positive
temperature anomalies have increased throughout the water column in the central
and eastern Pacific. 

The majority of models are on board for an El Niño
event. There are three charts I like to look at: the “Probabilistic ENSO
Forecast” from the Climate Prediction Center (CPC) and the International
Research Institute for Climate and Society (IRI), an IRI/CPC compilation of Niño
3.4 SST predictions from different dynamical and statistical models around the
world, and the Niño 3.4 SST predictions from the CPC’s own CFSv2 (Coupled
Forecast System Model, version 2). As the Probabilistic ENSO Forecast chart
below shows, there is a 60-70% chance of the El Niño lasting through 2015,
and our chances of a La Niña developing (cooler-than-normal waters in the
tropical Pacific) are small.

The IRI/CPC’s dynamical/statistical model compilation shows
all but one model forecasting above-average SST for the rest of the year, with
the majority predicting El Niño conditions. The thicker lines are the
averages of given models, and these also denote weak-to-moderate El Niño
conditions for the rest of 2015.

The CFSv2 also shows a moderate El Niño developing. The
solid black line is the measured SST in Niño 3.4 thus far, the colored lines
are forecasts from different “ensemble” members; i.e. forecasts using
slightly different initial conditions, and the dashed line is the average of
these ensemble members. 

For a more visual depiction of what this graph represents,
take a look at the sequence of images below. These images are based on the
above predictions from the CFSv2 model and show what the SST throughout the
tropical Pacific are forecast to look like as we head into 2015.

In conclusion, an El Niño is already developing, and
models are pretty confident that it will continue to strengthen and persist
throughout 2015 into next winter. The effects of El Niño for North America
are most pronounced during our winter, so if California gets buckets of rain
this summer, don’t drop down on your knees and praise El Niño just yet. On
the other hand, if California is getting swamped in the middle of the winter, well,
you’ll know who to worship. 

Charlie