It’s that time again. Let’s attempt to forecast the future out through the next few months, you know, that season everybody is obsessed with called winter! As usual, the focus here will be the combination of months that are meteorological winter and astronomical winter, so December through March, though if you follow social media and even some mainstream media you might have been lead to believe that winter started on September 23. Notice the obsession with winter (and summer) has become so intense that many people seemingly forget there are 2 other seasons, not that I need to remind you all here. As I mentioned in last year’s outlook and will remind you here, we don’t always see all of our “winter weather” fit neatly into the 4 month box we put the winter label on, as history has shown, but most of it does, so we focus on this period to forecast the expected character and behavior of the season. So let’s get to that now.
This year, the obvious big player is El Nino, our first in several years after a triple-dip La Nina for the last 3 winters. This El Nino is forecast to be fairly strong, peaking right in mid winter, so as a baseline we can start with some ideas based on what a strong El Nino typically means. And while there are variations in any El Nino, a strong one has often lead to a winter that tends to end up a little milder than normal. Snowfall has been variable in these events with a bit of a leaning toward the lower side of normal. Before we go into other indices and their potential impacts on our winter weather pattern, I should mention what I feel is a potential significant factor in the pattern, but with uncertainty based on an unprecedented nature of it, and that is the tremendous amount of water vapor still in the stratosphere as a result of the early 2022 eruption of the underwater volcano, Hunga Tonga, in the southern hemisphere. The largest eruptions we have observed in our time have been land volcanoes, which have put large amounts of ash and dust into the atmosphere, but never such a volume of water vapor. We know that the ash/dust clouds tend to act as a sun block, and lead to a global cooling event. We’ve already observed, not surprisingly, that the water vapor from H.T. has presented a greenhouse effect enhancement, with a spike in the global temperature very likely related to that event. In turn, there is some feeling through the scientific community that some of the tremendous precipitation events around the globe in the last year have a direct correlation to this, with some of the details not quite known since it’s really the first time we’ve observed this. One aspect of the pattern that I believe is linked to the H.T. Effect (HTE for future reference) is that it has induced a more persistent northern jet stream and also an increased frequency of high latitude blocking that was even prominent during the northern hemisphere summer. This would keep the pattern similar in many areas – where it’s wet, is stays wet (New England, for example, with a wet summer), and where it’s dry, it stays dry (Canadian wildfire season, for another example). I strongly believe we can’t ignore this potential effect going into and through the cold season, and one idea is that the blocking tendency may return after a current break. Or do we see something opposite to the warm season, and see a strong polar vortex hold on for a longer time? This is a question that will be answered by observing, since we don’t have much to go by. A strong PV would lead to a milder winter for much more of the season, while a stronger blocking regime, while allowing more cold, could also force the storm track further south, putting more precipitation into the Mid Atlantic and Southeast while the Northeast is drier, at least in terms of storminess from the subtropical jet. A continued stronger northern jet stream could still bring disturbances and significant temperature swings if it is displaced more to the south, versus staying north in a stronger PV situation. So you see the dilemma, while frustrating from a forecasting standpoint, fascinating from a science standpoint. My current leaning is that we see a mixture of both strong PV and weaker PV, but that the weaker PV periods prevail, leading to occurrences of both scenarios I outlined above. Other major indices need to be taken into consideration to help at least get an idea of how things can trend based on what we’ve observed with these, and as you know there are several of them, and many possible combinations, which of course can change as we go through the winter. Let’s take a look at some of the major indices and their current and expected trends as we go through the winter.
ENSO (El Nino Southern Oscillation): Currently in El Nino, predicted to be moderately strong, but recent trend has shown a bit of cooling (weakening) in the eastern equatorial Pacific while the western waters have warmed. We’ll have to watch this because the location of the warmest water does shift the overall impact of this index. Should even out somewhat with time but a bit of uncertainty in the overall picture. A stronger El Nino tends to produce a milder overall picture for winter in the Northeast.
QBO (Quasi-Biennial Oscillation, or the direction of stratospheric winds above the tropical latitudes): This was in a positive phase, westerly QBO, last winter, but is shifting into a negative phase or easterly QBO as we enter this winter. An easterly QBO tends to allow for more high latitude blocking.
AO (Arctic Oscillation, or another way of measuring the strength of the Polar Vortex aka PV): Currently moving into a weak negative phase where there is some disruption to the PV and lobes of it dip southward. This looks like it wants to continue into early December. This makes colder weather possible further south, including New England. Projections beyond, which become less confident with time, show a return to a solid positive AO around mid December where it may stay for quite a while, before trending back to neutral / negative later in the winter. A positive AO or stronger PV tends to bottle up arctic air and is generally a milder indication for our latitude.
NAO (North Atlantic Oscillation): One of the more well-known indices to follow but not all that predictable too far in advance. We can predict patterns that can lead to this index being positive or negative. A positive NAO tends to be a milder winter regime with no blocking and a more westerly flow across North America, allowing the Northeast to see milder intrusions of air from the Pacific in zonal flow and the southern US in a more amplified pattern. However, if we have an amplified pattern in which the trough is far enough east, we can have a cold pattern during a positive NAO. The negative NAO is characterized by low pressure south of high pressure in the North Atlantic, creating a block which deflects the jet stream and storm track to the south and opens the door for colder air and sometimes more storminess here in the Northeast. For this winter season, there may be a twist to this which I will talk about a little further along in this discussion.
PDO (Pacific Decadal Oscillation, a water temperature pattern in the mid latitude Pacific Ocean, north of 20 degrees N latitude): This index is often observed to be in a positive phase (cooler water west, warmer water east) during El Nino episodes, but currently this index is in a negative phase (warmer water west, cooler water east), which is not typical of El Nino. The negative phase of the PDO can limit the amount of storminess entering the US West Coast, and while the negative phase is projected to weaken, the PDO may remain at least somewhat negative well into winter. This could have an impact of limiting the amount of storms entering the US on the subtropical jet stream. The limitation may be minor, but is still a factor to be considered.
PNA (Pacific-North American Index, which describes the upper air pattern from the North Pacific into North America): When this index is positive, it’s associated with high pressure ridging in the western portion of North America and a tendency for low pressure troughing in the eastern portion of North America, which can be particularly pronounced in the US Southeast during an El Nino episode, in which positive PNA patterns tend to occur more frequently. However, right now, like the PDO, this index is opposite to what might be expected in El Nino, in a fairly strong negative phase, which tends to mean there is more troughing in the western US and more ridging in the East. The PNA is forecast to remain strongly negative through December before trending toward neutral at mid winter and positive later in the winter. However, during the short to medium term, the effects of the negative phase of this index will be mitigated somewhat by the negative AO allowing an unstable PV to send a series of troughs through the Northeast, suppressing high pressure ridging in the eastern US to the far Southeast and Gulf Coast region. During the course of the winter as this index slowly reversed, we’d see more troughs and a more active storm track for the US Southeast.
EPO (Eastern Pacific Oscillation, which is similar to NAO, but in the eastern North Pacific): A positive EPO is a mostly zonal or lower amplitude pattern which allows mild Pacific air into the US more readily, while a negative EPO features more high pressure ridging in the northeastern Pacific and Alaska, blocking Pacific air, and driving colder air southward out of Canada into the US, the longitude of the coldest determined at least in part by the placement of high pressure and downstream troughing. The EPO is expected to run in a negative phase into the first part of December, maybe to mid month, before trending to a neutral and eventually positive phase deeper into winter, but may hang around a neutral phase rather than going strongly positive into late winter, according to some long range simulation. This would put some limitation on Pacific flow. A negative EPO while the PNA is also negative can result in a dampened impact from both indices, which may be the case to start the winter, rendering them less powerful factors.
IOD (Indian Ocean Dipole, an index that measures water temperature tendencies in the Indian Ocean, and found to have some impact on the large scale climate pattern). A positive IOD features warmer water and increased convective activity in the western Indian Ocean and nearby land masses while cooler water dominates the eastern Indian Ocean with less convective activity and resultant rainfall for southeastern Asia as well as Australia. A negative IOD produces the opposite – cooler water in the western waters, warmer waters to the east with more convective activity and rain in southeastern Asia / Australia. The IOD will be in a strong positive phase to start the winter, with projections for a trend toward a neutral phase with time. A positive phase is correlated to a stronger PV in the northern hemisphere, which is expected to return after the current disruption.
MJO (Madden-Julian Oscillation, which describes convective focus in equatorial regions and has 8 phases depending on the location of the normally eastward-drifting convective wave): It’s known that the Northeast has a better shot at snow / wintry weather with MJO in phases, 1, 2, and 8. The MJO can also be strong, moderate, weak, and so weak it’s “in the circle” on the diagram, which indicates very little overall impact of this index. Currently as we head toward December, the MJO is moving through phases 8 and 1, and will reach 2 in early December, but while doing so it drops to very weak and its influence becomes less on the large scale patterns. This becomes a wildcard as we head into winter and is a potential spoiler for any long range forecasting. At times when we’ve seen this index get weak, it’s stayed that way for quite some time. Will that be the case this winter? It’s hard to say on that one. We’ll just have to watch to see if it becomes more of a factor with time.
Solar Cycle: This cycle, also known as the solar magnetic activity cycle, sunspot cycle, or Schwabe cycle, is a periodic (about 11 year) change in solar activity as measured by solar storms, or sunspots, on the sun’s surface. There has been a correlation observed that high periods of solar activity tend to correspond to milder winters overall, but this is not a solid correlation and more or a base guideline. A more useful aspect of the ability to measure this is to tell when we may see greater or fewer episodes of the aurora, and the potential for disruptions of satellite communication. Either way, Solar Cycle 25 (or the 25th cycle observed since we clearly identified this cycle in the mid 1800s) is expected to peak in 2024, so we’re about at the maximum for this particular cycle. Is that impacting our recent winters to make them milder, and will it do so with this one? How about a solid maybe?
Alright, did I leave anything out? Hmmm…. Well what can we say about long range forecasting, even after going over all of that, other than it’s not nearly as comfortable and confident a process as making a daily forecast for short to medium ranges. You can only do your best with what you know, and even what you don’t know. And speaking of things we don’t know, as I brought up earlier in the discussion, we have the HTE. Will the after effects from that volcanic eruption continue to be a player in the large scale global patterns and as a result the more regional scale weather events? I say yes. I do think our instances of blocking may be stronger due to it, but again this is an educated guess, and we will gain at least some insight on this, and other potential effects, by observing our patterns now and as the HTE lessens in the coming few (to possibly several) years, or however long it takes for the moisture in the stratosphere to return to normal. It’s going to be interesting.
So for the winter of 2023-2024, what are we looking at? It sounds almost silly to say there will be plenty of variability. You hear it in pretty much everyone’s forecast. You know why? Because we live in a place where the weather varies, normally. Will it have a strong tendency to be wet or dry, snowy or snowless, cold or warm? The aim of the long range forecast is to try to identify what these longer term trends will be. It almost doesn’t matter what the sum of them ends up being, because the impacts of temperature, wind, rain/snow are most strongly felt during the events, not so much over the entire season, but on an event-by-event basis. The longer term trends are more important for things like agriculture, or heating bills. People remember the 2014-2015 winter for its incredible stretch of snow and cold from the very end of January to the very beginning of March, and nearly forget that winter was almost “non existent” up until that point. They remember the individual storms in that stretch, and the stretch itself, but over a much shorter period of time than the entire winter. That may be a more extreme example of what I was speaking about above, but you get the idea. That said, I suspect when it’s over, we will look back on the 2023-2024 winter as not extreme in terms of temperatures, and not extreme in terms of storminess including snowfall. Odds favor more snow than last year in the coastal areas, mainly because snow was so hard to come by last year. Talk to somebody further inland and they don’t remember it quite this way. when you get to the western reaches of the WHW forecast area, snowfall was much closer to normal – even a little over normal in a few locations. What was that about variability? I don’t think we’ll have a gradient quite like that this coming winter, though time will tell. Let’s go with slightly below normal snowfall because I think our storm episodes may be lacking due to lower moisture, smaller events in the northern jet stream being more prominent than big moisture producers from the southern jet stream. Why? This would be due to some limitation of southern jet stream activity as mentioned when going through the indices above, and stronger blocking episodes forcing the subtropical (southern) jet stream to be more to the south than it might be – this is a guess based on the expected HTE. My month-by-month breakdown follows, quick and to the point, as I have pretty much described this all above already.
I can look into this month a little more clearly than further into the future, and we see what looks like a drier and colder than normal start to the month, followed by a milder trend at which time the pattern becomes a little more active. Lack of blocking makes the limited but still active southern jet stream send some systems our way, while a fairly regular northern jet stream supplies briefer cold shots later in the month. If we’re going to see a larger storm, we’ll need an anomalous system from the south or a good interaction of both jet streams. Cold start and milder finish combine for near normal temperatures and the dry start and uncertainty on how much we can squeeze out later in the month leads me to a near to below normal precipitation and snowfall forecast for the month.
This portion of winter may have the most questions to answer because when I combine all of the indices above, we see a lot of transition going on. I still think the predominant pattern will be mild as we lack blocking for the first part of the month at least, and our precipitation should be closer to normal as we can still sneak the southern jet closer during the non-blocking episodes, which may be dominant over blocking episodes. This will be the month when I’d expect most of the snow to fall in the region as a whole, ending up around normal, maybe even a little above normal favoring interior areas.
Enough of the indices lead me to believe this will be the month that features more high latitude blocking, strengthened by the HTE, and less Pacific influence due to a suppressed storm track, but more cold delivered from Canada. In summary, below normal for temperatures and precipitation / snowfall.
MARCH (UNTIL EQUINOX)
An easing of the February pattern, a little more normal for temperatures and precipitation / snowfall, and if February is indeed dry, this would appear as a “late surge of winter weather” while we look forward to the arrival of spring…
WINTER SEASON OVERALL
Temperature: Slightly above normal (departure +0.5F to +1.5F).
Precipitation: Slightly below normal (departure about -2 to -3 inches).
Snow: Below normal (due to fewer large events).
-Boston 35-45 inches
-Worcester 50-60 inches
-Providence 30-40 inches
-Hartford 45-55 inches