El Nino post write up for August

 

I’ve been trying to post these little updates on the developing El Nino every few weeks. This will cover the developing conditions in the Pacific.

El Nino and La Nina Explained

courtesy of NOAA’s National Ocean Service

The waters of the eastern tropical Pacific Ocean continue to warm as we approach the end of meteorological summer. This El Nino is expected to continue strengthening over the Fall, then reach its peak sometime in winter or early Spring 2024.

It’s only the middle of August now it’s pushing global temperatures to the 1.5 ºC climate threshold,

Sea Surface Temperature (SST) Anomaly …

 Global SST…

 

courtesy of Coral Reef Watch

 

Pacific SST…

 

 

courtesy of Coral Reef Watch

 

Atlantic SST…

 

 

Phases of El Nino…

There are East Based, Central Based, and West Based

Snow lovers hate East Based El Nino

Central Based (Modoki)

A Modoki is just when the greatest warm water anomalies are centered near the Dateline, this allows for a deep trough to setup south of the Aleutians.  While Modoki’s can be blocky in the Atlantic, that’s not always the case. Modoki’s are a mixed bag.   The trough in the Pacific shifts back and forth between the Gulf of Alaska and the Aleutian Islands, resulting in a up and down pattern, where high latitude blocking shifts west and east between Iceland and Canada. So, what type of winter events we see can vary greatly.  Modoki winters can experience wild swings in temperature, resulting in rain, mix, and snow events. It’s all about the timing of the cold air outbreaks and the current storm track.

West Based sets up closer to ideal, the 500 mb pattern along with the polar and subtropical jet, making for a better chance for a snowy season.

 

Currently we’re in a very strong East Based El Nino. But looking at the subsurface water temperature progression and other signs that this is shifting west.

  

Strength of El Nino…

Judging the impacts of an El Nino isn’t just about the phase of ENSO we are in. But we have to include the strength of the event too. You can have weak, moderate or strong El Nino phases. Typically, stronger El Nino’s bring more impactful weather to parts of the United States, especially for California and the southwest, compared to weaker El Nino phases.

 The strength is determined by how much above average the water temperatures are in the Niño 3.4 region.

.Weak El Nino (with a 0.5 to 0.9 SST anomaly), Moderate El Nino (1.0 to 1.4), Strong El Nino (1.5 to 1.9) and Very Strong (Super) (≥ 2.0) events.

The latest weekly SST departures are:

Niño 4 0.9ºC

Niño 3.4 1.2ºC

Niño 3 1.8ºC

Niño 1+2 3.3ºC

Currently the developing El Nino is considered moderate to strong. The northern hemisphere ocean/atmosphere system has coupled, with what is going on in the equatorial Pacific.  During El Nino we typically see an active northern polar jet, with an active and amplified southern sub-tropical jet. That has certainly been the case for the last several months.

We should note that, for historical context, the most accepted method of categorizing the intensity of El Nino’s and their opposite, La Nina’s, utilize NOAA's three-month running mean SST anomaly, known as the Oceanic Nino Index (ONI), instead of looking at one week or even one month's worth of data.

Subsurface water temperature.

 

Latest SOI index

The SOI is a tool we use to determine how the ocean and atmosphere dynamics are evolving.

 

The current SOI is indicating the atmosphere is responding to a weak to moderate El Nino signal.  This could be part of the reason for some of the disconnect we’re seeing in the ocean/atmosphere system. This is just one of the reasons this El Nino, isn’t acting as a typical El Nino would.  

 

 The most recent IRI plume indicates El Nino will persist through the Northern Hemisphere winter 2023-2024.

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Some of the factors in play…

Hunga Tonga-Hunga Ha'apai volcano (Yep, I’m still talking about it.) underwater eruption in the South Pacific Ocean occurred Jan. 13 to Jan. 15, 2022. The eruption blasted an enormous plume of water vapor and enormous quantities of ash and volcanic gases into Earth's stratosphere. All of this is still affecting the Stratosphere and in turn the troposphere

there are a number of other factors that have contributed to how this year has been, including going from La Nina to El Nino, the current Solar cycle, the Tonga-Hunga Ha'apai eruption leading to a reduction in atmospheric particulates allowing more sunlight to reach the surface. All of these factors, added to a generally warming planet. Mean the Planet is going to warm even more, and become much more volatile.  

All of this is changing the pattern, in ways that the outcome isn’t clear.  We have never had a super warm Atlantic Basin during an El Nino. This is having a big impact on the hurricane season. Typically, during El Nino, conditions over the tropical Atlantic are more hostile resulting in fewer tropical cyclones. But this year, the warm water in the Atlantic, is making for a likely above average season.   Like wise the Northeast has been extremely humid this summer, again that is the result of how all of these factors are interacting with each other. So, we’re more or less in uncharted territory when it comes to how this current El Nino is going to act like.  

A few thoughts on what this might mean for winter 2023-2024…

A winter outlook involves the speed and amount of Eurasia snow growth, sea ice extent, movement of the QBO, The very warm Global Oceans. And many other things. Much of these things we can’t look at for at least a couple of months; So, we have a long way to go, before an outlook can be released. So, while it’s way too early to talk about specifics, we can at least apply a broad brush to the subject.

We have to remember, no two El Nino’s are alike, when looking only at the five previous strong El Nino’s, there are some general commonalities to note headed into winter 2023-2024.

El Nino years following triple-dip La Nina.

. 1957, 1976, 2002, 2023

Some analogues I’m considering…

1957-1958, 1965-1966, 1972-1973, 1982-1983, 1986-1987, 2002-2003, 2015-2016.

 

An El Nino Modoki is just when the greatest warm water anomalies are centered near the Dateline, forcing a deep trough in a really nice spot south of the Aleutians. they're also quite blocky in the Atlantic

These analogues include East Based, Central Based and Western Based. I have to include all of them, because this El Nino is still strengthening and evolving.  But we are starting to see shifting forcing west.  So right now, we have a chance for a Motoki or even a west based El Nino event.  I’m leaning toward the idea of this being a hybrid Modoki and West Based event. But there is a chance this could end up as a basin wide event. This too would make for a fairly decent winter as well.

 The farther west this warming water can get the greater the likelihood for low pressure setup up in the western Aleutians, this would increase the odds for favorable high latitude blocking. How and where the blocking set up will be a major deal this winter. The QBO will also have a lot to say on how much blocking we see, a negative QBO and ascending would increase the odds for more blocking.

In general, Northeast and Middle Atlantic winters tend to be overall warmer and wetter during an El Nino. During strong El Nino’s we tend to see less overall snow. But as I’ve already said, no two El Nino’s are exactly the same.

During the super El Nino’s of 1982-83 and 1997-98 there were big 2nd half of winter snow events.

The winters of 1957-58 and 1965-66 were cold.

But El Nino is only one factor when it comes to how a winter will end up being. As I’ve already pointed out Blocking will be another major influence. Blocking involves the North Atlantic Oscillation (NAO)  

 

Here is a look at snowfall from 1950 to 2017 in nine Northeast Cities, broken down by El Nino, La Nina and neutral seasons, as well as those stronger El Nino seasons with a dominant positive or negative NAO.

We can see there is the sharp contrast in strong El Nino’s depending on whether they're dominated by a positive or negative NAO.

 The strong El Nino seasons dominated by a negative NAO produced the snowiest seasons.  More North Atlantic Ocean blocking of the jet stream in a negative NAO pattern would allow the polar jet stream to plunge southward in the eastern U.S., bringing ample cold air. A powerful subtropical jet stream, typical in strong El Nino seasons, would interact with the cold air, perhaps coupling with the nosediving polar jet, making East Coast snowstorms more possible.

 The 2009-10 season featured a moderate El Nino dominated by strongly negative NAO. The result was the snowiest season on record in Philadelphia and Washington D.C.  and the second-snowiest season in Pittsburgh. Conversely, with the exception of Washington D.C., all other Northeast cities tended to see the least snow during strong El Nino /positive NAO seasons. These seasons often featured the polar jet stream pushing cold air eastward across Canada rather than plunging deep into the East. With the dominant subtropical jet stream unable to meet cold air or interact with the polar jet, few Northeast snowstorms would result.

The bottom line, I’m still thinking this will be very strong El Nino, how this coming winter turns out will depend on the degree of blocking. The overall pattern is such that nobody is sure what kind of winter we’re going to see, but right now I’m thinking moderate to severe end of the spectrum.

Rebecca's, 2023 fall outlook

September 1st marks the beginning of meteorological fall. The meteorological fall covers three months, from September to November. This is the transition season from the warmest part of the year to the coldest part. So, for this reason, it can be quite dynamic. But the vast majority of people follow what it says on the Calendar. This is called astronomical fall (or the fall equinox) which starts on Sept. 23 this year.

The summer solstice occurs when the sun is directly over the Tropic of Cancer.  For every place north of the Tropic of Cancer, the sun is at its highest point in the sky and this is the longest day and shortest night of the year. The winter solstice occurs when the sun is directly over the Tropic of Capricorn and marks the shortest day and longest night of the year

During the equinox, the sun crosses the plane of Earth's equator, making nighttime and daytime (roughly) equal length all over the world. After the Spring equinox, the days begin to get longer as the summer solstice gets closer. After the fall equinox, the days begin to get shorter as the winter solstice gets closer.

But regardless of which definition you follow fall is about sweaters, pumpkin spiced lattes and the beautiful colors associated with the changing leaves.

This outlook will be based on meteorological fall.

 Keep in mind a seasonal outlook is an overall three-month trend. Weather forecasts are about the weather expected over the next few days. While seasonal outlooks say something about likely conditions averaged over the next few months. Seasonal forecasts provide information about these long-term averages.

When I do a seasonal outlook. I try to compile observational weather data from around the globe, I take these teleconnections and compare that against historical weather data, that are called analogues.  All of these metrics and data elements are used to come up with an overall idea for the coming season.  Based on that data, and many other factors including long range computer guidance… let’s take a look at how fall 2023 may be like.  Due to conflicting signals, I have a lower confidence in this outlook, than is typical for me.

 

Let’s look at….

A look at the current global Sea Surface Temperatures (SST) anomalies.   

 

The global SST forecast through October.

Images courtesy of the Australian Bureau of Meteorology.

The Pacific…

El Nino

This year’s El Nino started earlier than the average on the climatical schedule. Typically, El Nino starts in late summer or early fall. So, it has a lot of time to grow stronger over the fall. El Nino’s impact here in the Northeast in the summer and fall are hard to quantify, but most times, normally El Nino hits hardest in December through February, but given that this El Nino is one to two months early mean that we could see some impacts this fall.

During El Nino, on average the eastern CONUS sees cooler temperatures and drier than average conditions during the Summer.

 

Sea Surface Temperatures (SST) in the tropical Pacific are exceeding El Nino thresholds. Looking at the data, the El Nino is still rapidly intensifying

The current SST anomaly in the Nino 3.4 region (where El Nino is measured) is +0.865°C. So, we’re in a moderate El Nino

 

SST consolidation Nino 3.4 image courtesy of Tropical Tidbits.

The strength of an El Nino is determined by how much above average the water temperatures are in the Nino 3.4 region. The stronger the El Nino the greater it’s impacts. I posted in the blog, about what is a Super El Nino which you can find here.

Water temperatures 0.5ºC above average = Weak El Nino

Water temperatures 1.0ºC above average = Moderate El Nino

Water temperatures 1.5ºC above average = Strong El Nino

Water Temperatures of 2.0+ above average = Super El Nino

The Atmosphere in the Northern Hemisphere (NH) is farther along with coupling with the developing El Nino, than the Southern Hemisphere (SH), but the SH should come into line over the next few weeks. The dynamics are complicated, but essentially, we have to look at the Sea Surface Temperatures along the equator and also how the atmosphere is changing as a result of those warm SSTs.  

As the process continues, the El Nino will become very strong over the next couple of months, with water temperatures becoming well above average in the Nino 3.4 region (where El Nino is measured).  The SST could end up +2.5°C or more by the time we make it into the heart of Fall and through the coming winter.

 

 Monthly sea surface temperature anomalies for the NINO3.4 region image courtesy of the Australian Bureau of Meteorology.

 

A majority of the Global climate models are calling for SST in the equatorial Pacific to be at least 2.0ºC above average. So at least a strong El Nino is a good bet.

 

Image courtesy of the Australian Bureau of Meteorology.

 

Typically, during strong El Nino’s there is a persistent extended Pacific Jet Stream with an amplified storm track.

 

The Atlantic…

It’s a fact that most of the tropical and subtropical Atlantic are at or near record warm SST for this time of year.

 

 

images courtesy of Tropical Tidbits.

The super-hot Atlantic Basin Sea Surface Temperatures (SST) are going to be a big wild card, not only for the hurricane season, but also for the fall pattern. It remains to be seen how the very warm Atlantic will counter the impact of a moderate or strong El Nino, for that reason there are no great analogs for this fall

We have never seen a moderate to strong El Nino with Atlantic SST this war. Most other years with a very warm Atlantic either had neutral ENSO or La Nina.

These temperatures could correlate to warmer temperatures for parts of the CONUS.

 Other teleconnections...

Madden Julian Oscillation (MJO)

The NAO is currently weak it looks to stay weak for the next 7-10 days, then it should head more toward negative …leads to a blocky pattern

The Pacific North American Pattern (PNA)

PNA positive Associated with troughing in the Aleutian Islands and ridging in western Canada leading to more of a NW flow.

Atlantic Oscillation (AO)

AO negative means a slower hemispheric flow due to that higher latitude blocking

 The current pattern...

Is being driven by convection in the Pacific, which has the trough dominating in the Aleutians leading to a ridge over the western CONUS into western Canada as well as the overall troughing in the east.   

This is why we’ve seen all these stronger cold fronts dropping out of Canada and moving through the Northeast, driving out the warmer temperatures and high humidity. Then after a few days of cooler less humid air, we warm back up for a couple of days.  This back and forth looks to continue through at least the end of August

 

Month by Month…

 September

For temperatures:

The current active pattern with troughs dropping in out of Canada looks to basically continue. 

After a possible warm start, I’m leaning toward western PA, NYS and NE ending up average to slightly below average overall. While Western Pennsylvania into Maryland and Delaware ending up average to slightly above average

For precipitation:

I’m leaning toward the entire region ending up above average overall.

 

October

We should end up with ridging out west with more low pressure troughing over the Northeast

For temperatures:

I’m leaning toward the entire region seeing generally average temperatures overall.

For precipitation:

I’m leaning toward the entire region seeing generally being average overall.  With more of an active storm track over the Plains extending into the Great Lakes.

November

Based on how the pattern looks to go, November should feature above average heights over the Northwest US and Western Canada. This should lead to pronounced troughing over the Northeast. By November the El Nino should be quite strong 

For temperatures: 

I’m leaning toward the entire region ending up below average overall.

For precipitation:

I’m leaning toward far eastern Pennsylvania, New York State, New England into Maryland, Delaware and New Jersey above average overall. With the rest of Pennsylvania and Western Maryland well above average overall.

With the below average temperatures and above average precipitation, it could be a recipe for a few bouts of snow during November.

 

Frost freeze...

The date at which the first freezing temperature (32°F or less) is measured can occur at various times and locations in the United States. Year-to-year variability is expected due to various factors.

 

 Climatological date of median first 32 F freeze.

 image courtesy of US Dept of Commerce.

 Western New York State and Western Pennsylvania could see an earlier start to the frost/freeze season, with the rest of the region being closer to the climatological average.

 For mid to end of October given this idea of general troughing setting up, we should see parts of the Northeast see some snow events.

For November … an active jet stream, pulling moisture out of the Gulf into the Northeast, along with more in the way of colder conditions. I think most of the region will have a good chance of several mixed events and seeing at least one larger snow event, Maryland and Delaware, the odds for a larger snow event are rather low.

Breakdown...

But generally, this fall should be more in the way of wet than is typical.

Well, that’s it. I hope you enjoyed reading this outlook. I’m always grateful to be one of your trusted weather sources.