Brendan Heberton

We haven’t had to talk much about La Niña during the past few years. In fact, we
haven’t had much problem with it for quite some time. There are, however, a few
signs that show the Pacific cooling down a bit, and that is always something
that piques my interest. Just as a refresher, La Niña is the abnormal cooling of
the equatorial Pacific Ocean. A stout La Niña may look something like this from
2011:



Notice all of the “blue and green” scattered across the Pacific between South
America and Indonesia. Historically, a La Niña episode can produce this
generalized weather across the country.



Notice how the southern tier of states is usually drier than average. Well, the
current sea surface temperatures do not reflect a La Niña episode right now.



If anything, neutral to a slight Modoki El Niño is happening. But since the
fall, the Pacific has been cooling down. The map below shows that change…



This is especially true in the Northern Pacific Ocean. If this type of cooling
continues across the Central/Northern Pacific Ocean, it COULD set a better stage
for La Niña development later this year. While this is far from certain, some of
the latest computer model runs have suggested that is something worth looking
at... The graph below shows various computer model ENSO forecasts.



You can see that pretty much all of the models take things back toward “zero” or
neutral by the summer. Some of the models continue to go “below zero” which is
La Niña territory by late summer and fall. Of course, if this happens, this will
have impacts on our weather pattern as we head into the cold season next fall
and winter. Again, plenty of uncertainty here –– but one of the first signs of a
potential La Niña that we've seen in some years.

Another thing we are watching is the Pacific Decadal Oscillation (PDO). It has
dipped to its lowest level in years in recent months. The January value dipped
to -1.17. Again, the graph below shows what the PDO has looked like since 2012:



While we can have La Niña episodes when the PDO is positive, La Niña episodes
are much more frequent and longer lasting when the PDO is in negative territory.

La Niña is far from a certainty at this point, but it is certainly something we
are watching very closely. As many of you may know, La Niña episodes usually
portend significant drought potential across much of Southern Colorado and much
of the south/southwest states, which is why we will be watching this very
closely over the coming months.

La Niña potential later this year?