SOME BACKGROUND FOR FOLKS NEW TO ME
As you may or may not know, I am not an actual, degreed meteorologist.
What I am is a self-taught weather nut and enthusiast, and I’m passionate about the weather we experience. I love watching, studying and learning about our weather, and meteorology as a whole. It’s one of my two main passions, the other being music. I just want to be sure the public knows that I am not trying to present myself as something that I am not.
I study numerous broadcast meteorologists, commercial meteorologists, government meteorologists, and a select group of other enthusiasts like myself. I learn what I can online, and from reading lots of different technical discussions about short, mid, and long-term weather prognostications. In other words, I’m a weather curator, writer, reporter, and blogger.
I also have a pretty good intuition about our weather in Western Massachusetts, since I’ve been living here for close to 30 years now. I’ve seen enough patterns play out in our area’s micro-climates, and have seen enough busted forecasts to understand some of what transpires in our quirky little valley, given its unique terrain, along with the larger context of where it resides in the overall landscape of New England and nearby New York and eastern Canada.
REMAINDER OF WINTER 2016 OUTLOOK
Having said all THAT, I am going to offer for the first time ever, a forecast for the remainder of this Winter, based on what I’m reading and seeing with respect to the atmosphere in the northern hemisphere, both in the troposphere and the stratosphere.
To start, this Winter is going to be unlike the past three winters. If you ski, for example, southern New England will more likely than not be relying more on snow-making, than actual snowfall produced by Mother Nature. How can we ascertain this in advance? We can “read the tea leaves” so to speak by looking at what are called “teleconnections”, which are large-scale macro atmospheric patterns. Most of these patterns, while influenced by ocean currents, primarily are atmospheric dipole (i.e. two-extreme) oscillations of high and low pressure systems that are semi-permanent aspects of the atmosphere on Planet Earth. Some of them are not atmospheric, but oceanic in nature. Regardless, these teleconnections set the stage for the regional and local weather systems to play themselves out over the surface of the planet. The teleconnections “rough in” the synoptic (i.e. large scale) pattern, and then the regional and local weather plays itself out.
I am going to attempt to break down this discussion into 5 main sections. I will first discuss the Arctic Oscillation, which produces the cold air needed for snowy New England winters. Secondly, I will discuss the Southern Oscillation and El Nino, which is one way we can get storm production to flow into the U.S. and into New England. Without storms and their moisture, cold air doesn’t produce much snow. Thirdly, I will briefly discuss the East Pacific Oscillation and Pacific Decadal Oscillation which directs the cold air out of the Arctic and into the east. Fourthly (does such a word exist?), I will talk about the North Atlantic Oscillation, which can act as a block in the jet stream that slows storms down over our area, allowing higher snow production if all the other elements are in place. Finally, I will do my best to provide a brief summary of how I think things will shake out over western Mass. You can always scroll to the bottom to read the Summary, if you don’t want to know the whys and hows of my conclusions.
ARCTIC OSCILLATION (AO)
The one teleconnection that has arguably the largest role in how our winter weather plays out is called the Arctic Oscillation. You know this by its more familiar term, the dreaded and super scary POLAR VORTEX! BWAHAHA!
Well, that seems to be how some national media outlets frame this permanent phenomenon for their own business purposes. It’s actually not scary at all. Quite simply, it is a strong low pressure system that sits atop the globe over the North Pole. When it is strong, with a tight, and circular flow/shape, the Arctic Oscillation (or “AO”) is said to be in its positive phase. This positive phase keeps the cold Arctic air locked up in far northern Canada and the Arctic Circle. When pressures increase over the North Pole (i.e. higher pressure), causing a more wobbly, weakened and amorphous circulation, the AO is said to be in its negative phase.
As a snow lover or skier in New England, you want to see the negative phase of the Arctic Oscillation in play. This means that as the circulation weakens and becomes more wobbly, you get more releases of cold Arctic air down into the middle latitudes (e.g. New England), which results in plenty of cold air in our region. When this cold air becomes established, all we need are some ocean-influenced storm systems here in New England and we’re off to the races… or slopes, as the case may be.
As you can see from the graphic, the middle line is the demarcation from positive above, to negative below. A powerful Aleutian low a few weeks ago, and now a powerful Icelandic storm of about a week or so ago impacted the polar vortex, and have elongated it. This is going to allow more cold outbreaks to reach our shores, setting up the potential to see the snow fly.
EL NINO (ENSO) AND THE MADDEN-JULIAN OSCILLATION (MJO)
You can have lots of cold air in place, but if there are no storm systems tracking near our region, then you have cold and dry weather. So where will the storms come from this year? They will primarily be supplied by the Pacific Ocean and a more active subtropical jet stream, thanks to an oceanic oscillation that is now in a very strong El Nino phase.
As much as we’ve heard about the Polar Vortex the past two years, we’ve certainly heard plenty about El Nino this year, and for good reason. It is one of the Top 5 strongest El Nino events since records have been kept. Other very strong El Ninos occurred in the winter of 1982/1983, as well as 1997/1998.
Normally, strong easterly winds (a/k/a “easterlies) at the Equator in the Pacific push warm surface water to the west near Australia, allowing cool water to upwell along the northwestern South American coast. This is the positive phase of this oscillation, known as La Nina. However, when the easterlies weaken, that warm surface water expands east towards the aforementioned coast, and can create very warm ocean temps in the eastern Pacific, central Pacific, or both, as you can see in the graphic.
Without getting into too much detail around the various types of El Ninos and their specific influences, suffice it to say that the subtropical jet stream (the one that brings low pressure and moisture to the snow party), is very active this year thanks to this powerful El Nino. This, in turn, will produce a parade of storm systems out of the Pacific Ocean, and into the southern U.S. This gives us the storm potential we need to mix with cold air from the Arctic if we’re to see a snowy winter here in western Mass.
Another teleconnection we can look to, to give us an idea about available moisture for storms to work with is called the Madden-Julian Oscillation (MJO). The MJO is an eastward-propagating convection complex. What the heck does that mean? It means that along the Equatorial Indian and Pacific oceans, there is a convection process that migrates east from the central Indian Ocean to the east-central Pacific Ocean that is semi-permanent in nature.
Yeah but Dave, what the heck does convection mean? It refers to the process of air that rises and becomes buoyant due to warm air at the surface, and cold air up in the sky. Warm air is lighter than cold air, and will rise right up through it. The difference in air temperature over a vertical distance is called the lapse rate. As lapse rates become stronger (greater difference between cold and warm air over a shorter vertical distance), the more convection is fostered. As this rising air lifts up, it also releases latent heat as it condenses into clouds and rainfall, creating even more convection.
Anyway, to finish up, as these semi-permanent convection complexes migrate east, it can influence our weather here. As you can see from the graphics included, it is Phase 8, 1, and 2 that generally create cold phases in the eastern U.S. Currently, the MJO is moving into Phase 8 and forecast to move into Phase 1. So this supports the idea of the potential for more cold and moisture in our neck of the woods. There is much to learn about the MJO, but we can look at it in surface way to get a hint at what to expect here.
PACIFIC DECADAL OSCILLATION (PDO) AND EAST PACIFIC OSCILLATION (EPO)
So now that we’ve got cold air and storminess in play, what directs developing storms and cold air outbreaks into the eastern U.S., so that we see storms here, instead of the Mid-Atlantic, Midwest, the West, or the Southeast? We look to the teleconnections known as PDO and EPO that tend to set up the large-scale ridges and troughs that act as the main “shapes” of the atmospheric flow across the United States. These flows then direct warm and cold air to various locations. But just what am I referring to when I speak of ridges and troughs, any way?
Imagine looking at a shrunken version of the first 30000 feet of vertical atmosphere over the Pacific Ocean in front of you. Picture it as a rectangular box, with the surface shown as a line at the bottom of said box, and the vertical 6-mile mark in the sky as the line at the top. Now imagine a line of equal pressure, say 500 millibars, as a horizontal line half-way between the bottom line and the top line. While this surface of 500 millibars of pressure exists at that height (3 miles up) in our example, it can float higher in the atmosphere (a/k/a “ridging”, or a ridge), or float lower in the atmosphere (a/k/a “troughing”, or a trough). In other words, ridges are bulges in the vertical atmosphere associated with high pressure (fair weather), and troughs are depressions in the vertical atmosphere associated with low pressure (stormy weather).
The positive phase of the Pacific-Decadal Oscillation (PDO) is an oceanic oscillation that features warmer than normal ocean water just off the western U.S. coast and cooler than normal ocean water just off the coast of Japan. This helps create ridging in the western U.S.
The negative phase of the Eastern Pacific Oscillation (EPO) is an atmospheric oscillation that features higher pressures and heights in the northern part of the eastern Pacific, and lower pressures and heights in the southern part. This also helps create ridging in the western U.S.
As you can see in the graphics, we are in a positive PDO phase with warmer than normal ocean temps off the western U.S., and a negative EPO phase, with ridging in the northeastern Pacific near the west coast of the North American coast.
These two teleconnections help to establish strong ridges (like the winters of 2014 and 2015) in the western U.S. Correspondingly, strong troughs are then normally established in the eastern U.S. Air flows clockwise around the top of these ridges, bringing cold air from northwest Canada down into the east. The counterclockwise circulation around the trough in the east pulls this cold air down and in, and also directs storms up the east coast, delivering storminess into New England.
Both of these setups contribute to and can direct colder air into the east, as well as storm tracks in the general vicinity of New England, leading to colder and snowier winters in New England.
NORTH ATLANTIC OSCILLATION (NAO)
We can have a parade of snowstorms here, but if there is nothing to block the storm track upstream, then the storms are what weather folk call “progressive”, meaning they just keep progressing through and out of the region. “Upstream” refers to where the storm will track after it departs our region, vs. “downstream”, which refers to where the storm has tracked before reaching our area.
So if we want to see big snows in western Mass (i.e. a foot or more), where it’s normally much harder to get big snows due to distance from the coast, and hence most coastal storm tracks, we normally would need some atmospheric feature to slow down the progression of storm systems. This is where the Greenland Block comes into play (more scientifically known as the negative phase of the North Atlantic Oscillation, or NAO).
The North Atlantic Oscillation is another dipole teleconnection that relates to semi-permanent high and low pressure systems in the northern Atlantic Ocean. In the positive phase, lower pressures and heights are centered on either side (or on top of) Greenland, with higher pressures and heights in the northeast Atlantic Ocean near northern Europe and Scandinavia. With counterclockwise circulation near Greenland, this encourages storms near New England to keep on trucking through and out of here.
In the negative phase, higher pressures and heights form over Greenland. This clockwise flow brings air down out of the northeast, which accomplishes two things. First, it helps to funnel colder air down into our region, which can aid the development of coastal snowstorms. Second, as high pressure builds to our northeast, storms that are traveling up the east coast are forced to slow down near New England. Sometimes they stall and just “sit and spin”, they do loops like in the Blizzard of 1888 near Block Island and Martha’s Vineyard, or they just progress SLOWLY to the north and east. This allows them to dump more snow on western Mass and New England, and to strengthen further, if conditions are conducive. Now, you don’t always need a negative NAO setup for a storm to stall, but this can help.
Given all this, we can see in the graphic that the NAO is going into a negative phase, and forecast to be negative during much of January. And, the blocking pattern is to the west of Greenland, which is better for allowing snowstorms up the coast into our region.
SUMMARY
So here is what I think is going to happen. I’ve been watching these large-scale setups move around the atmospheric chess board for about a month now. I believe that the impact of El Nino is undeniable this year, given that we just had our first inch of real snow (sleet doesn’t count) in almost the middle of January.
I certainly feel that it will be warmer than the last two winters. We should see some coastal storms, but with warmer air getting into the atmospheric mix, this could lead to some more marginal events that include rain, sleet, freezing rain and/or wet snow.
Regardless, the teleconnections are indicating that a few major Nor’easters are possible, and we cannot rule out a blizzard or two. However, it’s tough to get the winds into and down to the surface of western Mass to produce a blizzard, given that we are 100 miles from either coast.
A big wild card is any blocking setups, which could suppress storms too far south, or even squashes them as they try to make it into our region.
Overall, I think we will be warmer than normal (either side of 32 degrees on average through Jan, Feb and March), and that snowfall will be below average to normal (normal is roughly about 35-40 inches in a season).
I hope you enjoyed this first stab at a Winter Outlook (well, rest-of-the-Winter Outlook), and I hope to do more of these types of outlooks going forward.
Thanks for reading,
Dave Hayes The Weather Nut