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  • Tim McGill

You Might Win A Prize For Checking Out My Winter Forecast For Chicago

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Many Memorable Chicago Snowstorms


I have survived five of the top ten worst snowstorms that Chicago has ever seen. The storms that I experienced as a kid were a lot more fun than the storms I have experienced as an adult. I learned to drive during the winter Chicago saw its most snowfall on record with just under 90" falling during the winter of 1978-1979. It was good practice because later in life I would have to drive through two blizzards (January 1-3, 1999 storm & the Groundhog's Day blizzard of 2011) to make it to work.


While I love forecasting winter storms, I don't enjoy most other aspects of them. Individual storms are enough of a challenge to forecast, let alone an entire winter. One thing I know for sure though is that winter is coming.



By winter, I mean meteorological winter, or the months of December, January and February. Last winter was a piece of cake according to the Accumulated Winter Season Severity Index, also known as the "misery index". Out of seven categories of severity from record mild on the good end of the spectrum to record extreme on the bad end, Chicago's winter was considered mild.



18.6" of snow fell during the winter months last season which was 9.5 inches less than the average of 28.1". The average temperature last winter was 31.4° or a whopping 5° warmer than the average of 26.4°. Below average snowfall and above average temperatures meant there was less misery to go around than usual for a winter in Chicago. So while it was a "mild" winter here you didn't have to go too far to be miserable. Just a five hour or so drive to the north in Wausau, Wisconsin the winter was considered severe. Wausau had nearly three times more snowfall than we did last winter.



Will we be more or less miserable this winter? That is the question I will try to answer in this post. Before diving in though, just a few more words of warning. Long term forecasts are not easy. Even those brave men and women that devote a lot more time and resources to this forecast of fickle weather than me will admit we have a long way to go when it comes to

seasonal forecasting. It is complicated with many influences that have to be considered and weighed against each other. What happens in one part of the world can impact weather several hundred or even thousands of miles away. Meteorologists call that a teleconnection.


This is how the American Meteorological Society defines teleconnections:


“1. A linkage between weather changes occurring in widely separated regions of the globe. 2. A significant positive or negative correlation in the fluctuations of a field at widely separated points. Most commonly applied to variability on monthly and longer timescales, the name refers to the fact that such correlations suggest that information is propagating between the distant points through the atmosphere.”


The most influential and important teleconnection that forecasters focus on for this winter forecast is the presence of a La Nina in the equatorial waters of the Pacific Ocean. The central and eastern tropical Pacific Ocean is expected to be cooler than average through this winter.


A La Nina winter tends to buckle the jet stream further south at times into the Midwest for intrusions of bitterly cold air. Portions of the country are wetter or drier than usual during this pattern and portions of the country are colder or warmer than usual. There are some definite connections. However, there are also parts of the country where the influence of a La Nina on its winter aren't entirely known.



Most models are forecasting a moderate to strong La Nina this winter. The further a model's line drops below the 0.0 line on the chart below the stronger the La Nina is forecast.


So with this in mind forecasters will look at "analogue years" or years when a similar magnitude La Nina occurred to see what those winters were like to help draw some conclusions about the upcoming winter. The graphics below shows average snowfall patterns for weak La Nina years (just below) and for strong La Nina years (further below). Stronger La Nina years tend to have less snowfall overall for most of the Midwest.




With this year's La Nina expected to be in the moderate to strong category, the analogue years tend to favor above average precipitation for Chicago and near normal temperatures but a lot of volatility with wild temperature swings during the course of the winter are also typical under these conditions.


NOAA's winter forecast was released recently and it seems to parallel the patterns we typically see in a La Nina winter. Drier and warmer than average weather in the south, colder than average from the northern plains to parts of the Pacific Northwest and more precipitation than average from the Midwest and Great Lakes through the northern tier states. Looking locally, their forecasts have equal chances of above or below temperatures overall for Chicago while we are favored for above average precipitation.




I have also considered winter forecasts from various private companies and specialized computer models that represent blends of forecasts from multiple models from both the United States and European weather agencies.


Here is an example of one of the model sources that I considered. The North American Multi-Model Ensemble (NMME) is a blend of several models used for seasonal forecasting. This forecast suggests the Midwest and most of the country will see above average temperatures overall this winter. I was careful to include the word "overall". There will undoubtedly be periods of colder than average weather this winter. This would suggest though that we end up being above average when all is said and done during the period of December 1st this year to February 28th, 2021.



I tallied up the snowfall and temperature forecasts from eight different forecast sources. I tried to fit those predictions into designated categories. Those categories were below average snowfall, around average snowfall, or above average snowfall. I did the same for the temperature forecasts. I tried to put them into the categories of either below average temperatures, near normal temperatures or above average temperatures. There were a few sources that were hard to fit into a specific category because it either wasn't included in their forecast or the forecast was vague. FYI, I did not include the Farmers' Almanac or Old Farmer's Almanac forecasts. They don't have a good history of showing any real skill but you can check out an older blog post for their forecasts just for fun.


The forecasts for temperatures this winter lean towards above average. I had six sources favoring above average temperatures, three near normal and only one below average.



TEMPERATURE FORECASTS THIS WINTER


For snowfall there seems to be an even clearer consensus. There were six sources favoring above average snowfall and one near normal. None of the sources was predicting below average snowfall.



SNOWFALL FORECASTS THIS WINTER

So upon further review there seems to be a strong signal for both above average temperatures this winter and above average snowfall.


I looked back at the last 30 winters to see how they stacked up compared to average. 14 of the last 30 winters had below average winter snowfall and 16 had above. 10 of the past 30 winters had a mean temperature below average, two were right at average and 18 were above average.


After careful consideration my official winter forecast is for a warmer than average winter in terms of temperatures overall. My prediction is that we will be 2° to 4° overall above average. I also believe snowfall will be above average or more than 28.1" total. My prediction is snowfall somewhere in the range of 31" to 37".


I look forward to March 1st when I can compare my forecast to what actually happened. If I am way off, I may accidently forget I ever posted this. In the meantime, I am going to buy a new snow shovel.


*Disclosure: Some of the links on my site are affiliate links, meaning, at no additional cost to you, I will earn a commission if you click through and make a purchase.


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