This piece is an examination and analysis of some of the factors that influence the outcomes of meteorological winter in the great state of Connecticut, and, to a broader extent, across New England as a whole, as while this piece is targeted towards Connecticut readers, many of the ideas apply to the greater region as well. We’ll focus primarily on December through February as those are the months that make up meteorological winter, but will also share our thoughts on March as well when appropriate. If you're just looking for a quick read and the forecast, we summarize that at the end of the piece, but I highly suggest you take some time and read the whole thing, as it will give you a much better understanding of why we think what we do.
Before we dive into this, a word of caution. Long-range outlooks are an extremely imperfect science, and, as with any forecast, is not the rule of thumb. To mitigate this somewhat, we try to work in probabilities and ranges rather than absolutes, to give a more reasonable boundary of what may happen, but things can and do change in meteorology on a dime, and, as a result, any long-range outlook, including this one, should be taken with a grain of salt, and seen as more informational rather than predictive. Nonetheless, we do strive to be as accurate as possible, and the science behind these methods is real, if a bit shaky at times. We'll keep an eye on how we're doing throughout the winter, and will likely have periodic updates to confirm or refine our thinking from this initial outlook.
With that out of the way, let’s dive into the forecast. Most long-range forecasts are built off of a variety of datasets, indices, models, and sources that are combined using some sort of weighted formula to produce a final product. For this forecast, we’ll examine the following datasets/information sources, and use the approximate weighting scheme below to weight them in the final forecast.
- Seasonal Models(~10%)
- Teleconnectors(NAO, AO, PNA, EPO, QBO, PDO, etc. Don’t worry, we’ll explain them as we get to them!) (~20%)
- Current conditions(SAI, SSW, Solar Activity, SST’s, etc.) (~15%)
- Gut feeling (~5%)
Let’s get started with the seasonal modeling. There are several long-range global models which attempt to model the upcoming months in much the same way that the midrange global models attempt to model the upcoming forecast period, that is, start with a set of initial observations and apply some physics package to those observations to make future forecasts for the next period on some interval, then, that forecast is fed back into the model as the initial observations for the next period to be created off of, and so on. As you can imagine, small inaccuracies in initial data or calculations are exponentially magnified as the recursive cycle continues, and as a result, global models, especially the seasonal ones, are notoriously inaccurate, hence our relatively low weight of them compared to other factors. However, they are still worth considering, just as much for what they don’t show as what they do show.
There are three major global models, of which we can legally show you two (The EURO seasonal comes from a paid service which we can’t reproduce, but it is in line with other guidance); the American CFS and the Japanese JAMSTEC.
Here’s a look at the forecasted temperature and precipitation anomalies from the CFS. Click an image to enlarge it(Here and throughout the discussion as well).
As far as precipitation goes, agreement is pretty good here for wetter than normal conditions across the eastern seaboard. Considering that if anything, the CFS has a dry bias, the argument from these models points strongly towards above normal precipitation for the winter in our area.
Overall summary of the long range models: Above normal temperatures and above normal precipitation.
Analog years, for those of you unaware, are years that had a similar upper air pattern throughout the fall and had similar values on the indexes and overall weather pattern. The CIPS has a model which analyzes the upper air data and returns a daily list of top analogs to fit that data. Looking through the results from the last several weeks, these winters pop up the most in that data and seem to have the best fit to the pattern that we’re seeing this fall when comparing various factors to the current conditions that we're seeing in ENSO, sea surface temperatures, and other teleconnectors.
Producing composite maps with that data gets us the following graphics for temperature and precipitation:
When breaking down the precipitation maps month by month, the result is essentially the same as the composite. That is not the case, however, with the temperature maps.
Overall Summary of the Analogs: Slightly above normal temperatures and above normal precipitation.
Here's a look at the progression of sea surface temperature anomalies in the ENSO region for the past few months.
Here's a static chart of the four key regions of El Nino and a look at their readings and trends, moving from west to east as you read down the page.
As El Nino continues to remain positive throughout the winter, and above normal precipitation along the eastern seaboard is strongly correlated with El Nino, I see no reason to refrain from weighting precipitation in this section as above normal. As far as temperatures go, we will leave them somewhat above normal, but also emphasize the trend towards a cooler second half of winter.
Overall Summary of ENSO: Above normal temperatures and above normal precipitation.
We mention and talk about the three main indices fairly regularly in our winter discussions, but if you need a refresher, or are just joining us this season, we'll explain them briefly. AO is the Arctic Oscillation, an index measuring pressure anomalies in the Arctic, and is correlated with temps for our area for the winter months. +AO suggests above normal temps, -AO below. The NAO is the North Atlantic Oscillation, and is a close relative of the AO, and it measures roughly the same thing in the North Atlantic. The NAO has a correlation with blocking in the atmosphere for storms; -NAO usually implies more blocking is available, +NAO represents a faster pattern with less room for storms to amplify. Finally, the PNA represents the ridge in the Pacific, and a +PNA usually correlates to below normal temperatures in the east, along with a stormier react, a –PNA cooler air out west and warmer air in the east.
Let's start with the PNA and the EPO(Eastern Pacific Oscillation). The couplet of +PNA and -EPO was what drove the extreme cold that we had last winter. While the EPO is not forecast to be as strongly negative as it was last winter, I do think we will see more volatile shifts in it's readings as the winter moves on. Traditionally, the EPO was measured by the strength of the warm pool in the Northeast Pacific, but as multiple factors play into this pattern, including the breakdown and cooling of El Nino, the convection generated by the MJO and ENSO, and more. El Nino is usually a catalyst to cooling in the EPO region, resulting in a more positive EPO, but this years Nino has done comparatively little cooling in that region compared to normal. As a result, confidence in the direction of the index is low, but I would argue for a more negative reading as the winter moves on and El Nino releases it's grip on our pattern somewhat. Another factor towards a more back-loaded winter...
The PNA, which is primarily driven by tropical forcing, is often less of a factor in El Nino winters, where the MJO(Madden Julian Oscillation, representing intensity and location of tropical forcing) plays much less of a role compared to in a neutral or La Nina winter, where strong ridges are formed by the pulses of forcing from the ENSO region. However, over the past several days, we have seen an intense pulse of tropical forcing from the MJO, and the result has been an almost Nina-like pattern, with a strong -PNA and a Southeast ridge across the CONUS as a result, bringing warm southern air up across the country and leading to warm temps nationwide. Should this strong tropical forcing continue, it would have a profound impact on the weather pattern, but for now, we will consider the PNA a relative non-factor, as I don't think it will be especially strong in either direction.
The PDO, or Pacific Decadal Oscillation, is expected to continue positive throughout the winter, as it is a roughly decadal(Meaning decade, or 10 years) index, and we are in roughly the second year of the positive cycle. A positive PDO generally is correlated with the attributes that a -EPO brings(Farther west GOA low, high latitude ridging, etc.), which results in the development of cooler conditions across our area. It is not an especially powerful index, and will probably be mostly outweighed by the stronger ENSO, but we will keep it in mind.
The QBO, or Quasi-Biennial-Oscillation, is expected to remain positive throughout the winter as it is in the middle of it's 12-15 month cycle, resulting in a weak correlation with a more stable and northerly Polar Vortex, which would result in warmer temperatures across the CONUS. It's a weak correlation though, so I don't put too much weight into it.
As far as the NAO and AO go, we will address those in more detail in the current conditions section when we talk about SAI, but for now, here are some model forecasts for their readings over the next 90 days. They fit the trend of the other wintry indexes to start out positive and then go negative as the winter continues. These come from the CFS, which is rather flawed as we describe above, so I won't put a whole lot of stock in them, but it's worth looking at.
Overall Summary of Teleconnectors: Variable, although in general agreement for a transition towards a colder second half of winter.
Here's a look at the extent of North American and Eurasian snow cover so far this fall plotted against recent history.
As far as the stratosphere and Sudden Stratospheric Warming go, solar activity looks to be on the downswing compared to last winter, and we are already coming off one of the lowest peaks in history in the solar cycle. As a result, the solar impediment to a SSW should be substantially less than last winter, perhaps providing the SAI with a better shot at success. While it's impossible to predict a SSW, I don't see anything in the means arguing for a lower than average shot at one, and certainly no hinderance to one in the form of solar like we saw last winter.
Here's a look at the current sea surface temperature anomalies.
Overall Summary of Current Conditions: Favorable for the development of a SSW and thus a -AO/-NAO, resulting in below normal temperatures in the latter parts of winter.
No maps or science here folks, just a gut feeling. Since May, I've been on the warm and wet train of thought with this winter, but still maintaining close to normal snowfall. While I think that much of December will be well above normal and rather rainy, I wouldn't be surprised to see a wet snow event or two work it's way into the forecast, especially towards the beginning of the month where a brief relaxation in the pattern looks possible. I am inclined to favor development of a -AO/-NAO in the second half of winter, primarily due to the SAI and diminishing Nino, and also because we're due, and while that doesn't have any scientific importance whatsoever, I've noticed that these things tend to work in cycles, and we're in need of some negatives in those departments to balance out the strong positives from previous winters. I wouldn't be surprised to see a more -EPO than the science argues for, as persistence is a strong concept in meteorology, and I'm not sure we'll see the dominant pattern of the past two winters go away as quickly as some think it will.
Overall Summary of Gut Feeling: Above normal temperatures and above normal precipitation, with near-normal snowfall.
To recap, here's what we came up with for each of the six factors that we analyzed.
- Overall summary of the long range models: Above normal temperatures and above normal precipitation.
- Overall Summary of the Analogs: Slightly above normal temperatures and above normal precipitation.
- Overall Summary of ENSO: Above average temperatures and above average precipitation.
- Overall Summary of Teleconnectors: Variable, although in general agreement for a transition towards a colder second half of winter.
- Overall Summary of Current Conditions: Favorable for the development of SSW and thus a -AO/-NAO, resulting in below normal temperatures in the latter parts of winter.
- Summary of Gut Feeling: Above normal temperatures and above normal precipitation, with near-normal snowfall.
Looking at all of this, precipitation is clearly weighted towards being above normal throughout the winter. I don't really see a reason to go against above normal precipitation, and thus, will go with a fairly wet winter as far as QPF goes, with a forecast of 120-160% of normal precipitation. I expect similar anomalies across all three winter months.
Temperatures are a bit trickier. While the means suggest above normal temperatures of varying intensities, I think there is a clear signal among the various factors for a cooling trend throughout winter. I don't think that February will be enough to negate the warmth that will be featured in December and the first parts of January, but I do think that it will be enough to put a substantial dent in it. My concern with going too warm is that if a SSW does develop and the AO/NAO state turns substantially negative along with a -EPO, it is very possible that we will see another well below normal February, which would result in a near-normal winter in the means, but I'm not going to go that far, as I do think it is somewhat questionable that we get that complete flip, and thus will forecast a range of 1-2 degrees above normal temperatures for the December-February mean, broken down into +3 to +4 in December, +1 to +2 in January, and -1 to -2 in February. I do think if we were to bust on temps, it would be high, but I'm not willing to commit to near-normal quite yet considering the strong signals for a warm start to winter.
As far as snowfall goes, I think we'll see slightly below to near normal snowfall. While we will see above normal precipitation, we will also see above normal temperatures, resulting in, at least for the start of the winter, quite a bit of rain across the region. While it wouldn't shock me for us to see an early season heavy wet snow event in early to mid December as the pattern temporarily relaxes, I think that we'll be waiting until 2016 for sustained periods of snow and cold. I do think that we will see above normal snowfall in February, however, and that is where we will make up quite a bit of our deficit to that point, likely continuing into the first part of March as well. While I think we will average slightly below normal in the means, it only takes one or two big events with the right timing to change the seasonal totals dramatically, and so I'll leave a small window for above-average snow on the upper end of the range, and call for 75% to 115% of normal snowfall. I think that the further inland you are, the closer you will be to normal snowfall, and especially see the possibility for a substantial seasonal total in northwest Connecticut, where temperatures could be just cold enough to allow for substantial snow in some of the borderline events that we will no doubt see this winter. I think we'll be playing with the rain/snow line a lot more than we did last winter, and as a result, the interior will look to be the big winners this year.
To recap, the official SCW Winter Forecast:
- Temperatures averaging 1-2 degrees above normal throughout the winter, broken down into 3-4 degrees above normal in December, 1-2 degrees above normal in January, and 1 to 2 degrees below normal in February.
- 120% to 160% of normal precipitation, spread evenly throughout the winter.
- 75% to 115% of normal snowfall, focused more towards the back end of the winter.
The Winter Ahead
That about wraps up the forecast portion of this discussion, but before we say farewell for now, a few general housekeeping items to cover. As you may know, we post on a reduced schedule during the off-season, with discussions generally being issued 2-3x per week. Over the next couple of weeks, we will begin to ramp up to our winter schedule, which features daily discussions with more detailed storm forecasts as needed. By the end of November, we will be posting daily, if not before then.
Our discussions are posted here on our website, and are linked to from our Facebook and sometimes our Twitter. We will also post shorter, rapid-fire type updates only on Facebook from time to time, and we hope to be more active on Twitter this winter than we have been in the past. We have heard your calls for a mobile app loudly and clearly, and are researching ways that we can create an app that would allow us to easily share our content with you in a format that still allows for the presentation of model information, yet is optimized to mobile. We'll keep you updated as we move forward with that project.
Finally, we're looking for a forecaster or two to join our team for the upcoming winter. If you or someone you know would be interested in joining us, send an email to firstname.lastname@example.org and cc email@example.com. Include a brief description of why you want to work with us, your forecasting experience/meteorological background, and a sample of something weather-related that you've written in the past. We welcome meteorologists and experienced hobbyists alike who are looking for a platform to reach an audience that numbered over half a million readers last winter and is growing every single day. Please keep in mind that this is not a full time position, nor is it an opportunity for you to advertise your personal work on our platform. We're looking for someone who loves weather, loves(and is very good at) writing about it, and wants to partner with one of the leading sources for weather in Connecticut and one of the premier hobbyist-run platforms in the country. If this sounds like you, we want to hear from you!
It looks like that's all we've got for this edition of the SCW Winter Forecast. On behalf of Tim Wrightington Jr. and Greg Petridis, I'd like to thank you for reading this years Winter Forecast, and I certainly hope that if you liked it, you will pass it along to your friends, family, and anyone else who you think would enjoy it. As always, we'd love to hear your thoughts, and are more than happy to answer any questions you may have. Leave a comment on this post or shoot me an email at firstname.lastname@example.org and we'll get back to you as soon as we can!
Until next time, I remain,
Yours in Connecticut Meteorology,
Partner and Lead Forecaster, Southern Connecticut Weather
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