Some of y’all have been asking why this past winter was so warm with a lack of blocking and snowfall. I’m sure many of Y’all have the same question. So here is a post that will try to explain what is going on. I’m a Meteorologist not a Climatologist. But I do have an understanding of Climatology, so we will see how well I do!
I’ve been posting a few writeups dealing with the
changing climate, in things like the spring and hurricane outlooks. This post
will take a look at possible reasons for last winter being so warm and snowless.
When we look back at Sea Surface Temperatures on the 13th of February and compare that to now, we can see there have been a lot of changes in the ENSO region of the equatorial Pacific. Nino region 1+2 and in Nino region 3 is starting to cool. Looking at the subsurface water temperatures anomalies, we can see there is a lot of cooler water just below the surface.
During the last 4 weeks, above-average SSTs have weakened across most of the equatorial Pacific Ocean
So, this El Nino is going to flip to La Nina conditions very quickly.
I’ve mentioned The Tonga’s Hunga volcanic eruption that
happened in 2022 many times. It released an enormous amount of water vapor into
the atmosphere. The shear amount of water vapor is in part to blame for the
recent warming in the Northern Hemisphere. The water vapor is going to continue
to cause havoc for several more years. But the volcanic eruption can’t account for
the last several years of warm winters. So, what else is going on?
To answer that we have to look at the state of the
Pacific and Atlantic.
We’ve had a positive Pacific Decadal Oscillation (PDO) for the last few years. We also have warm SSTs north of the ENSO regions. All of this constitutes mixed signals. Helping to counter what’s going on inside the ENSO regions.
The Atlantic is also very warm. The tropical Atlantic
is experiencing well above average SST.
During El Nino/La Nina there are characteristics that
are expected, take for example my winter outlook, I based things on the strong
El Nino, the overall pattern did resemble what you would expect for an El Nino.
But activity in the subtropical jet has been slightly out of what you would
expect. Why is that?
The El Nino hasn’t exerted much influence on the atmosphere. Based on Oceanic Nino Index (ONI) [The ONI is based on SST departures from average in the Niño 3.4 region, and is a principal measure for monitoring, assessing, and predicting ENSO] tropical SSTs, Nino 3.4 showed a strong El Nino over the Winter. But the Southern Osculation Index (SOI) hasn’t responded like it should have. The SOI has been indicating a weak to moderate El Nino. This disconnect is very important, as what was going on with the Pacific SST, where the El Nino wasn’t really coupling with the atmosphere, which threw off the tropical forcing.
Based on the data in a paper by Michelle L. L’Heureux with the Climate Prediction Center (CPC), we could see La Nina begin around mid-May. I won’t get into the research in the paper, but if you want to read it, here is a link to the paper.
A Relative Sea Surface Temperature Index for Classifying ENSO Events in a Changing Climate.
The CPC images, do agree with that.
Here is my theory…
The Atlantic is the other side of the issue. It is
quite possibly the bigger part of the equation. The super warm SST in the Atlantic is playing
havoc with teleconnections like the Artic Oscillation (AO) and North Atlantic Oscillation
(NAO). The warm waters are affecting the polar jet stream and promoting
troughing in the west and ridging in the east, this is one reason why the
western CONUS has been experiencing colder winters over the last several years.
The much warmer than usual water in the Atlantic, is most likely having an
impact on the Atlantic Meridional Overturning Circulation (AMOC). The AMOC is
like a conveyor belt, where the warm salty water in the tropical Atlantic flows
north, meets the colder water in the northern Atlantic, which allows the warm
water to cool and become denser and sinks, then this colder air moves south as
deeper currents along the North American Coast. All of this explains the very
warm water in the Gulf of Maine, and along the Middle Atlantic Coast. This
circulating water has a cascading impact around the globe and is a big player
in world climate.
The AMOC has an effect on the Atlantic Multidecadal Oscillation as well. The last few winters haven’t had
a lot of high latitude blocking near Greenland. The poleward moisture and heat
transport from the tropics is affecting the NAO and AO. Since blocking most of the time coincides with
negative phases of the NAO and AO. The blocking helps the Northeast experience cold during the winter, and helps improve snowfall across the region. The warming is interfering with the sub
polar low and the subtropical high making both stronger than average. This is
allowing the NAO to stay in a persistent positive phase. When the NAO is positive, the Northeast is much more likely to see a warmer winter. Subsequently the high
latitude blocking is influenced by many oscillations. All of this is influencing
storm tracks and is altering wind patterns. This in turn is affecting seasonal
temperatures in the Northeast. So the pattern becomes slightly out of tune, making things warmer; along with a storm track that makes it much harder for things to phase, which makes having big snowstorms more difficult.
There is no doubt that the global climate is warming. Since
the 1980’s a large part of the CONUS has been trending warmer. The Northeast is
one of the fastest warming regions, but it’s the Arctic that’s seeing the most
warming. This warming is melting sea ice. The melted ice flows into the Atlantic, this
fresh water dilutes the saltiness, which impacts the AMOC. Research has shown
that the AMOC is losing stability and is slowing Down. The warming Atlantic
Ocean water has a big hand in making northeast winters milder, much like
drought begets drought, our warming winters feed on themselves. The lack of ice
and snow, ends up reflecting sunlight back to space, so the ground absorbs more
heat, driving temperatures higher. As a result, there are higher odds of a storm
bringing rain instead of snow.
There are examples in the past, that show this same general
pattern. One of these is the Medieval Warm Period that occurred around 900 A.D.
to the mid 1300’s. A.D. Increased solar activity and a decrease in
volcanic activity, brought about changes in the NAO, which brought about warmer
winters and wetter conditions to Europe and eastern North America. Core samples
show that Nordic Seas became well above average. The very warm water caused a
lot of ice loss in the arctic. As we’re seeing now, this melted ice worked its
way into the Atlantic, the fresh water from the melted ice, eventually cooled
the ocean which resulted in the AMOC Slowing down and then collapsing. So, the
very warm conditions in the late 1300s quickly turn to unprecedented cold
conditions in the early 1400s, only two decades later. We know this through
core samples and tree rings. This was the beginning of the Little Ice Age,
which lasted roughly from the 1400’s to the end of the 1800’s or beginning of
the 1900’s.
I’m not saying what’s happening now is going to lead to
an event like the Little Ice Age. I’m just drawing a parallel between what
looks to be going on and a similar event in the past. This means winter here in the Northeast is
going to continue to be a casualty of what’s going on for the foreseeable
future we're still going to get these snowy storms, but very snowy winters are
going to become harder and harder to occur.
There is a lot of debate about natural factors causing
all of this VS humankind causing all the warming. But regardless of which side
you take, we’re stuck with the fact that the climate is warming. And this
warming is not only impacting the climate but also the weather.
IMO a lot of what is going on with the warming has to do with natural cycles and water vapor. I’ve never said that humankind isn’t lending a helping hand. There is no doubt that part of the warming climate is due to human activities. But I think a large part of what is going on is the ocean/atmosphere system and cycles, many of which we know nothing about. I’ve posted many blog post on this subject. You can find them in the blog.
All of this makes longer range forecasting challenging. we're going to have to adapt to the changes that are going on. This is a steep learning curve. We can still use past events to forecast. But we're going to have to alter the rules and tweak things a bit.
