Being in the weather business means that we often get asked a lot of questions about the weather. These questions range from simple to complex, but one of the most common ones that we are asked is this: ‘Is this weather normal?’ This question came up often after the Polar Vortex that consumed the Midwest for over almost a week in January and snow piles seemingly growing exponentially since then.
The answer to the most recent round of that question is simply put: yes. However, it may not always feel that way due to varying weather patterns and trickery by Mother Nature. One of the common myths many people hold about weather is that they can expect temperatures to hang near the averages each day of the month, which is an expectation that will lead to disappointment as weather can be affected by so many variables.
One of the primary variables that weather is affected by is the jet stream, which changes based on the temperature differences between the north and south latitudes. These temperature differentials are greatest from mid-fall until mid-spring, moving the track of the jet stream towards the middle latitudes where most of the Midwestern parts of the United States lie.
This shift in the jet stream brings what meteorologists call an ‘amplified pattern’ with large swings from warm to cold temperatures and varying snowfall amounts. However, these ‘amplified patterns’ vary greatly from year to year.
For example, December brought mild temperatures and relatively little snowfall to the Midwest. These weather patterns led many to expect that the remainder of the winter would remain relatively mild. The Polar Vortex that set in during the last week of January proved that expectation to be false. While startling, this “flip” in weather is not unusual in the slightest.
While the Polar Vortex intrusion into the US was certainly newsworthy, this is not the first time parts of North America have experienced this, with the winter of 2013-2014 the most recent before this year.
While these patterns may be considered normal, temperatures have been rising by 0.5 to 1.0 degrees over the past few decades in most areas of the country, especially major cities. This is due in part to the phenomena known as an ‘urban heat island.’ This is the idea that developed cities contain more concrete than past and have more physical activity than past generations leading to a far greater retention of heat. This heat retention is one factor contributing to warmer environments, particularly around cities.
While weather events can vary from year-to-year, it is still possible to accurately predict temperatures and snowfall with models. Most of the time meteorologists can use models to predict temperatures within just a few degrees within the immediate three days, with demonstrable value out through 7 days.
If you are beginning to wonder if winter will ever end, just know that the jet stream is preparing to shift within the next few weeks and should deliver warmer temperatures to most of the country. That will surely melt the snow that is piling up, particularly in the Midwest.