INTRODUCTION
Good day to you, kind patron of my online interactive weather reporting for western Mass and beyond! I wanted to compile this Winter Weather Outlook Report for the upcoming 2018-2019 winter season to give you a general idea of what we can expect.
I get that you might be wicked busy, and if that’s the case, you can just scroll to the bottom and get the simple summary which gives you a surface idea of what things are looking like. But if you actually enjoy learning about the weather and some of the drivers of winter weather in New England, then I strongly suggest you read the entire report which goes into some detail and provides some education about how things are looking for the next three or four months.
Before I jump into the report, let’s establish a few definitions of key terms that will continue to be mentioned throughout the report. Check those out below, and then read the report. Thanks so much for your support, and I hope you enjoy the outlook!
KEY DEFINITIONS
RIDGE
Ridges refer to higher than average atmospheric pressure at a given elevation in the Troposphere (the part of our atmosphere where our weather transpires). This based on a recent 30-year average, usually 1981-2010.
To determine the strength of a ridge, meteorologists use an elevation level that is usually measured at 500 millibars of pressure.
What does that mean?
In meteorology, surfaces of equal pressure that roughly parallel the Earth’s surface are measured in terms of the elevation at which those pressure surfaces usually reside. For example, the 500mb surface averages an elevation of about 18,000 feet, or 3.5 miles above our heads. This is roughly the middle of the Troposphere.
When a ridge forms, the 500mb pressure surface rides higher than that average 18000 foot level, sometimes quite a bit higher. When these outward atmospheric bulges form, they promote sinking and warming air underneath them, and generally fair weather.
TROUGH
Inversely, troughs refer to lower than average atmospheric pressure at a given elevation in the Troposphere.
When a trough forms, the 500mb pressure surface rides lower than that average 18000 foot level. When these inward atmospheric depressions form, they promote rising and cooling air underneath them, and generally inclement or stormy weather.
TELECONNECTION
There exists on this planet large, basin-wide and continent-wide oceanic and atmospheric patterns and relationships between areas of warmer and cooler water, and areas of higher and lower pressures. Many times these paired extremes oscillate over short, medium or long periods of time, between two ends of a spectrum (a spectrum based on sea surface temperatures or atmospheric pressures).
These global, large-scale patterns are called teleconnections, and they help us broad-brush future weather conditions over large regions which help to paint a general picture of likely weather impacts in terms of a winter seasonal outlook. The day to day and week to week weather impacts are further refined as we get closer to each day that we’re fortunate enough to live through.
OCEANIC VS. ATMOSPHERIC TELECONNECTIONS
In terms of a winter outlook, we look to the oceanic teleconnections first as they receive solar energy from our star, become variously cooler and warmer, and then help to drive the atmospheric teleconnections above them and across the land masses of our planet. Of course, the oceans the atmosphere impact each other in a constant interplay, but the oceanic patterns are the primary drivers.
This means that for the Northern Hemisphere, the ENSO (Equatorial Pacific), PDO (Mid/High Latitude Pacific) and AMO (Mid/High Latitude Atlantic) oceanic teleconnections are the place to start as we peer into the upcoming Winter season of 2018-2019.
ENSO (El Nino Southern Oscillation)
ENSO is a teleconnection that looks at the ocean temperature anomalies of the equatorial Pacific Ocean between Australia and northwestern South America. Sometimes you can have a basin-wide warming of the sea surface waters, and at other times only a section can be the predominant area of warming.
This year features such a setup, as it is the central area of the equatorial Pacific that is warmer than average when compared with the eastern or western equatorial Pacific. In the following animation, you can see that the majority of the warmer sea surface temperature departures from average are in the central Pacific.
And while some surface warming has indeed transpired in the eastern equatorial Pacific, you can see in the next animation that ocean temps are cooling just below the surface of that region, which is expected to continue.
The warming in the central Pacific fosters the strongest convection (i.e. thunderstorm development) in the middle of the equatorial Pacific. All of this inclement weather tends to force the formation of a trough north of it in the central Pacific and/or north-central Pacific, to the south of the Aleutian Islands/Alaska. A trough in this position tends to promote the formation of ridges along the west coast, which in turn tend to promote the formation of troughs in the central and eastern United States.
As previously mentioned, ridges promote clockwise flow, sinking air, high pressure, and fair/milder weather conditions, and troughs promote counterclockwise flow, rising air, low pressure, and stormier/colder weather conditions. You can see this ridge west / trough east setup forecasted in the graphic below.
In addition, the latent heat that is released into the atmosphere from this intense convection travels downstream, which is to the north and east. This heat tends to also help strengthen ridge development along the west coast. Central-based El Nino setups are also known to contribute to an active southern jet stream track, which is the kind that delivers storms along the southern U.S. so they can tap the Gulf of Mexico moisture, and then the warmer Atlantic Ocean waters off the southeast U.S. If these turn up the coast and mix with cold air in the northeast U.S., you get classic New England snowstorms with cold, snow, ice and wind. We should see a few of these Winter, I believe.
PDO (Pacific Decadal Oscillation)
The PDO is an oceanic teleconnection currently in a positive phase characterized by warmer than average ocean waters in the eastern Pacific and northern Pacific south of Alaska, and cooler waters in the north-central pacific. The PDO was positive in the Winter of 2014-2015, and you may remember that winter was stormy and cold, albeit with a late start in late January. It produced an epic winter for Boston with record snowfall. You can see the warmer waters south of Alaska, and just west of Canada and the U.S. below.
Positive PDOs tend to promote ridging in the western U.S. and western Canada, which helps to produce troughs in the central and eastern U.S., which in turn promote east coast winter storms. The PDO this winter should help foster a stormier New England this winter.
AMO (Atlantic Multidecadal Oscillation)
The AMO is an oceanic teleconnection currently in a positive phase characterized by warmer than average ocean sea surface temperatures in the North Atlantic Ocean, between the Equator and Greenland, roughly speaking.
When ocean temps are warmer than average across all data collection points, the AMO is said to be in its positive phase. When cooler than average, it is in its negative phase. This teleconnection has an oscillation period of around 50-80 years.
We are currently in the positive phase, and there is some correlation to that being supportive of snowier than average winters. However, of the three oceanic teleconnections that can be analyzed in seasonal outlooks for the Northern Hemisphere, this is the one that is least understood. However, it is somewhat supportive, so I thought I’d mention it.
AO (Arctic Oscillation)
The Arctic Oscillation to the Troposphere is what the Polar Vortex is to the Stratosphere (the atmospheric layer immediately above the Troposphere, and with which it interacts or “couples”). In other words, the smaller circulation of the coldest Arctic air in the Stratosphere (a/k/a The Polar Vortex) sits atop the larger circulation of the coldest Arctic air in the Troposphere just above the planet’s surface (a/k/a the Arctic Oscillation).
When it is strong, this circulation around the north pole and Arctic keeps cold air bottled up in the high latitudes and away from New England. The AO is thus said to be in its positive phase. This is exactly what happened in the Winter of 2015-2016 when one of the strongest east-based El Ninos ever recorded dominated and gave us a very mild winter, with very few Arctic air intrusions into New England.
However, when the Arctic Oscillation is weakened, whether by Sudden Stratospheric Warming Events (which is currently occurring), or by low solar activity (we are entering a solar minimum), or an easterly-based stratospheric wind referred to as a negative QBO (we have this in place for at least the first half of this Winter), it becomes wobbly and spills “lobes” of colder Arctic air that southward into New England. When this happens, the AO is said to be in its negative phase, and you can see below that in early January it is forecast to be in its negative phase.
(PLEASE NOTE: I will discuss SSWEs, QBO and Solar Minimum in a bit more detail further down in this report.)
Given a moderate to major Sudden Stratospheric Warming Event underway now and forecast to run through the end of December, along with the fact that we are entering a Solar Minimum and are seeing the end of a negative QBO, this should produce a negative AO in much of January and February, which will promote the spillage of Arctic air into the mid-latitudes where we live and breathe. Given the other patterns alluded to in this report, and it looks like this Arctic air should be directed into New England at times, producing cold and snowy periods.
EPO (Eastern Pacific Oscillation)
The EPO is an atmospheric teleconnection which tends to dovetail, more or less, with how the PDO is presenting. When it is in its negative phase, it refers to ridging above the eastern Pacific Ocean next to the western U.S., with corresponding troughing further south near and to the east of the Hawaiian islands. Given how the Pacific oceanic teleconnections are presenting this season, it looks like we’ll see periods of negative EPO, which will foster colder temperatures and inclement weather in the eastern U.S.
WILD CARDS (SHORT-TERM TELECONNECTIONS)
MJO (Madden-Julian Oscillation)
This teleconnection’s oscillation from one end phase to the other has a much shorter temporal scale, somewhere around 1 to 2 months.
There are 8 phases of the MJO that correlate to where this eastward-propagating area of intense convection is, anywhere from India eastward into the central equatorial Pacific Ocean at any given time.
The first, second, and eighth phase are the ones that create convection that releases latent heat downstream and aids in the formation of troughs and ridges that position themselves to allow colder air to spill into New England.
While we have to get into the winter to see how this may aid or hinder winter weather here in southern New England, there does appear to be some connection between the cooler ocean waters we now see north and northwest of Australia (near Papua New Guinea) and the colder phases of the MJO.
Whether produced by the eastward-propagating MJO convection activity, or the stationary ENSO convection activity, tropical Pacific convection has primary impacts on our weather in the U.S. and New England, and especially during the winter time.
NAO (North Atlantic Oscillation)
The North Atlantic Oscillation, when it is in its negative phase, produces high pressure and ridging near Greenland, with lower pressure and troughing in the northeast Atlantic.
When you hear the terms “Greenland Block” or “high-latitude blocking” it is referring to the negative NAO. Some of the stratospheric factors detailed below should produce at least a couple of blocking events north of our region this winter. When this happens, it slows down coastal storms, and also helps to direct cold into our region, or retain cold in our region, so this is supportive of the colder and snowier look for this winter.
STRATOSPHERIC FACTORS
QBO (Quasi-Biennial Oscillation)
The QBO simply refers to the predominant equatorial zonal wind up in the Stratosphere. When that high zonal wind is blowing from west to east, it tends to keep the cold Arctic air bottled up over the north pole, producing a stronger Arctic Oscillation and Polar Vortex. When this high zonal wind is blowing from east to west, it tends to cause high latitude blocking as well as SSWEs, which weaken the polar circulation and allow colder air to spill into New England.
Currently, the QBO is switching from east-based (negative) to west-based (positive), and you can see that in the chart below.
I do believe that this is one of the factors causing the current SSWE, and will likely provide enough support this winter before becoming entirely west-based to help support a snowier and colder winter ahead.
SSWE (Sudden Stratospheric Warming Events)
A Sudden Stratospheric Warming Event simply refers to a rapid warm-up in stratospheric temperatures over the high-latitudes and Arctic Circle. When this happens, it can split, displace, or change the orientation of the Polar Vortex. These effects then can “downwell” into the Troposphere and weaken the Arctic Oscillation, which in turn causes cold air to invade New England.
A substantial SSWE is transpiring as I type this report, and is forecast to continue through December. The red colors in the map below indicate much higher than average pressures in the Stratosphere over the Arctic Circle, which indicates stratospheric warming.
Because there is usually a lag time of 2-3 weeks between the event’s completion and the effects of it here in New England, this is also supportive of a colder and snowier outbreak by the middle of January, give or take a few days, as is supported by the map below.
During some winters we see several of these events that are more moderate in nature. In this case, we may be dealing with one large event, which would tend to produce a longer contiguous period of winter weather in New England in January, Feburary and into March. We shall see.
Solar Minimum
As you can see in the chart below, we are entering a Solar Minimum, which refers to a dearth of sunspot activity.
It is thought that this lack of solar activity allows ozone levels to increase in the Stratosphere. Rising ozone levels tend to allow the Stratosphere to warm. As we discussed above, a warming stratosphere can cause a weakened polar circulation and colder outbreaks into the mid-latitudes where New England resides.
TROPICAL ACTIVITY, AUTUMNAL CONTINENTAL SNOW PACKS, AND ANALOG YEARS
I follow and learn from many meteorologists, and there appears to be some correlation, even if it is not well understood, between land falling Gulf of Mexico hurricanes into the southeast U.S. and Pacific land falling hurricanes and tropical systems into the southwest U.S. Both types of tropical events happened this year, and it’s been thought that they can precede colder and snowier northeast U.S. winters.
There is also some correlation to Siberian snowpack south of the 60N latitude line, as well as to Canadian snow pack in its ability to both direct colder air into our region, as well as to modify (and thereby make colder) air that travels over Canada and into the U.S. One thought is that Siberian cold air (partially due to snow pack) produces ridges above it, which leads to troughs over the Aleutians, which leads to ridges over the western U.S., and then troughs over the eastern U.S. Much research needs to continue regarding this area, but we have seen supportive snow packs in both regions this past Autumn.
Finally, years where the state of the Pacific Ocean and the Pacific and the North American troposphere looked similar in late Autumn can be used as analogs to get an idea of how the winter season may proceed. The winters of 2002-2003 and 2014-2015 exhibited similar setups and both produced colder and snowier winters during January, February and March on average. You can see in the map below by Ben Noll that February is looking to be cold and snowy overall, and this is expected to linger into at least the first half of March.
CONCLUSION/SUMMARY
–After a cold start with a snowstorm in November, I believe that are seeing our January thaw come early in December this year. Today (Friday, December 21) was the peak of that mild surge.
–The week ahead features some seasonable weather, and a few additional mild days, and this seesaw may last into the first week of January as winter begins to load
–As I alluded to in the preceding report, all teleconnective signals are indicating we are about to plunge into a snowier and colder than average winter in southern New England
–This should begin by the second week or so in January
–Mid-January, and especially February are looking snowy and cold
–This pattern should last into the first couple weeks of March
–Some milder sub-patterns will no doubt arise, bringing the potential for ice and/or rain at times, in addition to an expected snowier and colder than average winter season.
–An earlier (and essentially on-time) arrival of Spring seems more likely than not in 2019, which is a departure from last year when cold hung on well into April
Ok, folks, that about does it. It’s a three-month look ahead, so it’s bound to not follow the letter of the law, but I wanted to let you know what I’m seeing on this first day of Winter.
I wanted to take a moment to wish you a very Happy New Year and a Merry Christmas if you are celebrating. I hope 2019 is your most gratifying, successful, and love-filled year yet.
In addition, I’m sending a boatload of gratitude and thankfulness to you for being a supporter and financial patron of my work!
Without you, I wouldn’t be able to devote the time necessary to do what I do. I hope I can continue to earn your support in the years to come so I can continue to do what I love, share what I’m seeing in my atmospheric periscope with you, and to answer your questions that help you best plan your life from week to week.
Take good care and get ready for some snow!
Sincerely, Dave Hayes (The Weather Nut)