Why a mild start to winter points to a frigid second half
Monday, January 14, 2019, 9:08 PM - For millions of residents of southern Ontario, this winter has not yet matched expectations based on our winter forecast. Regardless of whether you view this as a pleasant surprise or as a disappointment, you may be wondering what happened to winter, and, perhaps more importantly, can we expect more of the same until spring? This article will discuss the most common questions that we are being asked about the winter and look ahead as the rest of the season.
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There is no question that the start of this winter has not been living up to what one would expect from a winter that was forecast to be "colder than normal." It is important to keep in mind, though, that all seasonal forecasts are designed to give a snap shot of the season as a whole -- essentially an overview of how the season will be remembered.
However, we don’t believe that the final chapter has been written on how winter 2018-2019 will be remembered. Our forecast did highlight that the cold would be most persistent and severe during the second half of the season. We still believe that this winter will be remembered more for what is yet to come rather than what we've seen through early January, but we will have to wait until the end of winter to evaluate the accuracy of that forecast.
WHEN WILL CONSISTENT WINTER WEATHER ARRIVE?
We are already in the process of making the transition into a much colder pattern, as very cold air is already in the forecast for southern Ontario. While milder weather will attempt to fight back at times, going forward the breaks from the colder weather will be much quicker and not as warm as what we have been seeing during the past month.
WATCH BELOW: JET STREAM PATTERN
During the last third of January we expect that much colder than normal temperatures will dominate, with the potential for a period of frigid weather during the final week of January and into early February. Colder than normal weather is expected to continue through February and deep into March.
WHAT ABOUT SNOW? WILL WE SEE ANY SNOW STORMS?
Very cold patterns are often lacking in snow and our winter forecast did not call for a snowy winter. We predicted that the dominant storm track would be to our south and then into Atlantic Canada, which has been the case so far and we expect that this pattern will continue.
However, all it would take would take for us to get a high impact snow storm would be for a storm to deviate from the dominant track and pass just to the south of our region. This is possible (especially during the final 10 days of January), but not something that we can forecast with a high level of confidence this far in advance. Exact storm tracks (and resulting snow totals) often remain uncertain until just a few days advance.
What we can say that we are less likely to see significant rain during the last week of January and most of February and the pattern supports several clipper-type systems through our region. Also, a cold pattern with the Great Lakes wide open (for now) would produce an abundance of lake effect snow for the snow belt areas to the east and southeast of the lakes.
SINCE THE START OF WINTER DIDN’T MATCH EXPECTATIONS, WHY SHOULD WE BELIEVE YOU NOW?
I acknowledge that we could blow the forecast for the rest of the winter – that is always a risk when forecasting the future. However, as strange as it sounds, the mild start to winter has actually increased our confidence that very cold weather will dominate during the second half of winter. To explain, I need to give a very quick overview of how we developed the forecast.
In developing our seasonal forecasts, we do evaluate about ten different models, but we spend much more time evaluating global patterns, especially sea surface temperature patterns and where we find regions of colder vs. warmer than normal water. We then look for years in history that had similar patterns and analyze the weather that was associated with those years. The years that we identify as having similar patterns and useful for helping to predict the upcoming season are called analogue years. A key to a successful forecast is correctly identifying the right analogue years.
The analogue years that we identified for this highlighted the potential for a mild December, an inconsistent January that trended colder during the second half of the month, and a very cold February. So, why did we go with our research for the second half of winter, but not highlight the mild start to winter? I have asked myself the question countless times during this stretch of mild weather!
When we issued the winter forecast, we were still in the middle of the persistent cold pattern that dominated November and we could see that it would continue into the first week of December. Numerous models also kept trending colder for December. Given how persistent the cold had already been, it was hard to dismiss what many models were saying for December (despite our research).
So, while I regret not highlighting a milder start to winter in our winter forecast, a gentle start to the winter season is not a reason to abandon the forecast for the rest of winter. In fact, it increases our confidence that our research was on the right track after all.
The winter that is currently the closest match to this winter was four years ago, the winter of 2014-2015. That year we had unusual cold and snow during November and a mild December (even warmer than this year). Most of January was inconsistent with alternating periods of cold and mild weather and like this year everyone was asking “what happened to winter?” However, when the winter was over, very few people could remember much about December and January because of what happened afterwards, when Toronto recorded its second coldest February on record.
Does that mean this February was as severe as February 2015? No, not necessarily, but we do think that it has the potential to be memorable. This also a good example of why one should not write off the entire season in early January -- there is still a lot of winter left to go.