2023 2024 winter outlook part two

 

Part two will cover what this year’s tropical activity can tell us, snow cover in Siberia, and talk about some of the teleconnections like the Pacific Decadal Oscillation.

To read part one follow this link

I've been working on this and trying to figure out the best way to present it in the most concise straightforward and easy to understand format. Which is far from an easy task. 

I’ve tried to take a balanced approach to what I’m seeing this year. Remember a winter outlook is an overview of what the entire winter season should feature. This outlook isn’t going to cover storm details on snow amounts or track, it will feature a broad overlook of the general pattern we will likely see at times during this winter.

 

Sea Surface Temperature (SST) anomalies…

 

Teleconnections:

Our atmosphere is very fluid. These fluid properties are constantly changing over time and location. What’s going on over one part of the Planet has a downstream impact somewhere else.  A deepening ridge, means a trough must dig.  The weather patterns in other parts of the world are called teleconnections.

During the winter, changes in the phases of certain teleconnections can produce conditions favorable for a cold and snowy pattern in the Northeast and Mid-Atlantic Region. Besides the El Nino Southern Oscillation (ENSO) the other teleconnections we generally look at are the Artic Oscillation (AO), Eastern Pacific Oscillation (EPO), North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), and Pacific-North American Pattern (PNA).

 

The El Nino Southern Oscillation (ENSO)…

One of the winter major forecast factors to look at in the late fall/winter is the state of the ENSO. The ENSO is a fluctuating weather pattern around the equator in the Pacific. The cool negative phase is called La Nina where we see cooler than average sea-surface temperatures equatorial Pacific, the warm positive phase is called El Nino where we see warmer than average sea-surface temperatures in the equatorial Pacific.  Part, one talks about how this years ENSO and the developing El Nino are shaping up.    

 

El Nino

A lot of people including many meteorologists are placing a lot of importance on this El Nino and how it may be a Super El Nino. But while a moderate to strong El Nino is likely; we could fall short of super El Nino status.  

This isn’t going to be a normal El Nino

Strong El Nino’s  1957-58,1965-66,1973-74,82-83,1991-92,1997-98,2009-10,-2015-16

During El Nino we typically see a less-active, west-to-east storm track across the northern US. The subtropical Jet stream is also typically quite active.

Why was the Atlantic tropical season so active?

We had recorded warm water.

But the shear didn’t tear them apart as much

Could it be due to the placement of that shear?

The warm water in the Indian Ocean (a positive IOD) is one major reason. Another reason is the record warmth in the Atlantic Basin.

So, we got a lot of convection (rising air) around Africa and a lot of subsidence (sinking air) around the South Pacific Islands, that helps displace a lot of the lifting. So, we had rising air near and around Africa and lifting air over the Eastern into Central Atlantic. But we had sinking air in the Caribbean and Gulf of Mexico, so we didn't see much development in a large part of the Caribbean and GOM. The warm Atlantic overruled El Nino conditions.  

Typically, South America is very wet during an El Nino. But this year South America is experiencing major drought

So, it looks like the warm water around the Equatorial regions, shifted El Nino’s influence east, resulting in a very active 2023 hurricane season.

  

 We also have to look at the northern Pacific…

 

The Pacific Decadal Oscillation (PDO)

 The PDO deals with sea surface temperature anomalies over the Northern Pacific (north of 20° north latitude), as with all teleconnections it has a positive and negative phase. These phases typically last for decades. The PDO represents the oceans response to the atmosphere.  In this way it is a prime driver for low pressure systems in the north Pacific, for example the Aleutian low-pressure system in the Gulf of Alaska. Depending on how strong this low is, it will have a different impact on wind flow, and the pressure gradient. If the Aleutian Low is very strong, we tend to see a stronger southernly flow along the immediate West Coast.

The positive phase is characterized by cool SSTs north of Hawaii and warmer than average SSTs in the Gulf of Alaska and along the West Coast of North America. The negative phase we see the opposite, warmer than average SSTs north of Hawaii and cooler than average SSTs in the Gulf of Alaska and along the West Coast of North America.

During the positive phase the Mid-Atlantic and Northeast is more likely to experience overall below average temperatures for December, January and February. During the negative phase the opposite is true, with the Mid-Atlantic and Northeast likely to experience overall above average temperatures for December, January and February.

The PDO has been negative for the last several winters. But the last couple of months has seeing it quickly moving towards neutral after being negative for the last four straight years. The last time this setup occurred was during the Fall of 2002. The winter that followed was a very decent winter snow wise here in the Northeast.

So, while this is theoretically a negative PDO. it really isn’t a textbook negative PDO. During a typical negative PDO the water is much colder in the Gulf of Alaska and west coast of Alaska, the cold water would also typically extend down into the Pacific Northwest. So, while the water is cooler it isn’t as cold as you would expect to see during a negative PDO.

The PDO and the Pacific North American Pattern (PNA)

There is a direct correlation link between the PDO and the PNA. During the winter the correlation is greater than 0.80.

The PNA is closely related to the strength of the Aleutian Low and the strength of the PDO

The PNA for our purposes here, is the PNA is the main driver of the trough ridge pattern over North America

During a negative PNA there typically is more overall upper level troughing over the western U.S leading to cooler and wetter conditions, while the eastern U.S. is more likely to see overall ridging leading to drier and warmer conditions. During a positive PNA the eastern U.S. sees more in the way of troughing while the western U.S. sees more in the way of ridging.   

 

Last winter, we had a negative PDO and a negative PNA during January and February that combination resulted in very warm temperatures across the Northeast and Mid-Atlantic Region.

 

The PDO and the ENSO

During El Nino, the Aleutian Low is generally stronger than average during the winter months; this favors a positive PDO pattern. The opposite is true during La Nina; the Aleutian Low is generally weaker than average during the winter months, which favors a negative PDO pattern.

A negative PDO favors a weaker El Nino or a stronger La Nina. A positive PDO favors a stronger and longer lasting El Nino or a weaker La Nina

This is going to be at least a moderate El Nino winter, with a strong likelihood of the El Nino being strong. So, since this isn’t a La Nina year. There is a strong signal that this winter will feature a positive PDO. What we’re seeing in the SSTs in the northern Pacific supports this idea, of a developing positive PDO.

 

When the PDO and the PNA are in opposite phases, they are working against each other (Destructive interference)

 

As I said above, the other major teleconnections we look at during the winter are the AO, EPO, and the NAO. Unlike the ENSO PDO and to a lesser extent the PNA; these three have a tendency to fluctuate between phases every couple of weeks or so.   

 

Artic Oscillation (AO)

The AO deals with the strength of the Polar Vortex (PV) and determines whether or not there will be a supply of Arctic air available to fuel winter weather. I will explain more about the PV when I discuss the current snow cover. But, a positive AO indicates that the PV will be strong and Arctic air will stay locked up near the pole while a negative AO indicates the potential for a weaker PV leading to the chance for Arctic air to escape southward.

Eastern Pacific Oscillation (EPO)

During the winter, the state of the EPO controls whether there is, a cross-polar path for very cold Arctic and Siberian air to flow across the pole and down into central and eastern North America.  During a negative EPO, a ridge builds over Alaska. The more amplified this ridge is, the greater the chance for cross-polar flow. Conversely, a positive EPO indicates a large, persistent low in the Gulf of Alaska and results in warmer weather for the lower 48.

 

 

North Atlantic Oscillation (NAO)

The NAO, in its negative state, indicates high-latitude blocking over Greenland. This lingering area of high pressure causes the flow to stagnate. The storm track is often underneath it and can result in persistent storminess for the Eastern US. On the contrary, a positive NAO has no such block and the storm track moves quickly across the CONUS and out into the Atlantic.

Can the eastern US still get winter weather with a positive NAO? Yes, but they’re often quick-hitters and rarely significant events.

The ideal configuration for a period of winter weather in the eastern US is a negative NAO, negative AO, negative EPO, positive PDO and a positive PNA. Can other combinations still produce winter weather? Sure, but this combination is almost a guarantee.

 

Snow cover:

Since it is still October, I remain focused on the snow cover advance across Siberia and what impact it may have on the stratospheric polar vortex (PV).  I am sure I will be discussing this pathway more in the coming months.  More extensive snow cover across Eurasia in October, and this mostly confined to Siberia, the more likely the PV will be weaker than normal during the winter months that favors widespread colder temperatures across the Northern Hemisphere (NH) but in particular in East Asia and the US east of the Rockies.

The more widespread snow cover is across Siberia during October, the more we’re likely to see a weaker than average stratospheric Polar Vortex (PV) during December through February. The PV is a large area of low pressure that sits over the Pole during the winter. When snow cover in Siberia is above average, it favors the negative phase of the Arctic Oscillation (AO).  When the Arctic Oscillation is in its positive phase, the jet stream, which brings us  a large part of our weather in middle latitudes, tends to shift to the north. So, when the AO is positive, the polar vortex is generally strong and in a tight circle, with cold air bottled up over the Arctic. When the AO is negative, the PV tends to be weak and much wavier meaning it is prone to collapse, this increases the likelihood of cold outbreaks here in the U.S. east of the Rockies.  

So far this year, snow cover over Siberia has been well below average, but over the last couple of weeks this departure has been reversing. Snow cover over northern Canada isn’t really seeing any big improvement in snow cover. But in general, the larger the snow cover extent in Asia and Canada in the Fall, the better the chances for stronger polar air outbreaks during the winter.

 

We will have to keep an eye on this; as there is still time for the snow cover over Canada and Eurasia to increase.  

 

Here is what I’m thinking based on how things look to be trending….

Right now, the closest the atmospheric setup and pattern resemble is the winters of 2002-2003 and 2009-2010. Those winters saw generally colder temperatures and some snowy periods

I do think we’re going to have a predominate positive PDO and positive PNA. This would allow for the potential for cooler overall temperatures for the winter of 2023-2024 here in the Northeast and Middle Atlantic. But storm tracks and temperatures will depend on the phases of the AO, NAO and EPO.

Real winter will be slow to start, with overall temperatures in December running average to slightly above average. January will see generally average overall temperatures. Then February into March will see overall temperatures below average.  This isn’t going to be the coldest winter on record; but it also won’t be the warmest winter on record. Those predicting a torch for the entire winter are likely on the wrong side of what looks to transpire.

There will be blocking setting up near Greenland at times. Depending on how the polar vortex acts during those times will determine the amount of cold that will be available.  

We’ve already had some early season nor’easters. I think the winter is going to feature a few nor’easters that come up the Coast from the Gulf of Mexico (Miller A nor’easters) and some storms that move into the Ohio Valley that then transfer to the Middle Atlantic Coast (Miller B nor’easters). The tracks will depend on the alinement of the teleconnections, if we have a negative AO along with a negative west-based NAO, it would favor a snowstorm bringing the chance meaningful snow for parts of the region. But if the negative NAO is east-based, the storms would likely form too far east to bring much in the way of snow to parts of the region.  How much cold these storms have will depend on the phase of the EPO, if the timing works out, then a negative EPO would bring the opportunity for at least a moderate polar airmass over the region.  

The amount of snow this winter will be very dependent on your location. Those in western parts of our region, will likely see overall snow amounts that are average to below average, with central and northern parts of the region ending up generally with overall average seasonal snow amounts. Those in the Middle Atlantic into southern New England, will have the greatest chance of seeing overall above average seasonal snow totals.  The winter pattern that looks to be setting up will likely see at least one to two big nor’easter events from mid-January, February into early March.  These storms would have the potential to bring major snowfall across the Middle Atlantic, I-95 Corridor into Southern New England. We’ve seen these kinds of winters before, where one or two big storms made up the bulk of the winter snow.   

 

Well that’s it for now.

Part three can be found here