A resource of Biophilia: Pittsburgh, #bioPGH is a weekly blog and social media series that aims to encourage both children and adults to reconnect with nature and enjoy what each of our distinctive seasons has to offer. 

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It has been a chilly few weeks in the 'Burgh! Ice has been starting to form on the Allegheny, Mon, and Ohio Rivers, and the temperature has been below freezing since Christmas Day. Winter is thoroughly reminding us what time of year it is, but let’s check out this extra cold winter weather, shall we?

If you remember from our discussion about the winter solstice and the spring equinox, the Earth sits at slight angle on its orbital axis. As we make our year-long stroll around the sun, for part of the year, the Northern Hemisphere is tilted away from the sun, resulting in less direct sunlight. This is the source behind our winter and the shortness of daylight hours. For the other part of the year, though, we are tilted towards the sun — resulting in more direct sunlight, our summer season and longer periods of daylight. This time of year for us in the Northern Hemisphere, it’s colder than summer because we are receiving less direct sunlight than in the summer. However, down in the Southern Hemisphere, where it is currently summer, all of that is reversed since they are receiving more direct sunlight.

Since it is winter, we can expect winter weather, but what is causing this particular cold snap? We can certainly expect changes in daily weather; constant shifts in air pressure and water vapor in the atmosphere lead to fluctuations what we experience as weather. This extra cold stretch, though, seems to have an additional player: the jet stream.

Before we can wrap our heads around the jet stream acting as Jack Frost, let’s do a bit more exploring into what a jet stream actually is. In broad terms, a jet stream is a “river of air,” or fast-moving winds, that wraps around the globe and separates a cold air mass from a warm air mass. Our polar jet stream in particular is the boundary between the cold air around the Arctic and the warmer air coming from the south or equatorial regions, but the “river of air” doesn’t follow a single path around the globe; it ribbons and weaves north and south, constantly moving and shifting and bringing fluctuations in weather along with it. Currently, the jet stream has sunk even as far south as Florida, bringing a chilly blast of Arctic air into a subtropical world of palm trees. Similarly, across the Atlantic, the UK is expecting a cold snap of Scandinavian temperatures from the jet stream moving south.

To some degree, these bursts of cold are fairly normal. It’s winter — it’s supposed to be cold! Plus, the jet stream is dynamic, constantly moving and bending, and changing the local weather as it goes. However, over the past several years, scientists have been trying to unravel the connection between the jet stream activity and the extent of sea ice in the Arctic, which appear to be linked. Over the past few decades, the extent, or total area, of winter Arctic sea ice has been decreasing. In fact, December 2017 showed the second-lowest extent of Arctic sea ice for that month since satellite monitoring began in 1979 (the record lowest for the month of December was in 2016). As sea ice has decreased, and accompanying warm temperatures in the Arctic enhance further sea ice loss, scientists have observed evidence suggesting that the decrease in sea has led to a weakening in the jet stream, which leads to changes in jet stream activity. It should be noted, though, as with any arising trends, the scientific is community is as level-headed as ever and urges that thorough research should be done before we jump to conclusions. So on the one hand, a cold snap is perfectly normal. On the other hand, well… it’s always a good idea to keep the future in mind and be a good steward with our resources. And for now, bundle up!

Connecting to the Outdoors Tip: While it might be brisk outdoors, a family can still explore some data of the natural world from the comfort of the indoors. The National Weather Service has an abundance of data available freely online — what kinds of questions can you ask and answer? With your school-aged students, practice data collection by creating a table of weather conditions (temp high, temp low, precipitation, etc.) and filling out the table every day for a week to monitor how the weather changes. Remember, though! Weather and climate are two different things. Look for monthly temperature averages from both Pittsburgh and a city from another state. How are the averages different? How far apart are the locations? Why might the climate be the same or different from the two different areas?

Continue the Conversation: Share your nature discoveries with our community by posting to Twitter and Instagram with hashtag #bioPGH, and R.S.V.P. to attend our next Biophilia: Pittsburgh meeting.

Resources

Francis and Vavrus 2015: Evidence for a wavier jet stream in response to rapid Arctic warming

Kretschmer et al. 2017: More-Persistent Weak Stratospheric Polar Vortex States Linked to Cold Extremes 

Screen 2013: Influence of Arctic Sea Ice on European Precipitation

National Snow and Ice Data Center: Arctic Sea Ice News and Analysis

Reuters: Record-shattering Cold Reaches into Florida 

AccuWeather: What are jet streams and how do they influence the weather we experience? 

National Weather Service: The Jet Stream

Scientific American: The Arctic is Getting Crazy 

Weather Channel: Jet stream change to drag Scandinavian chill towards the UK 

Kim et al 2014: Weakening of the Stratospheric Polar Vortex by Arctic Sea Ice Loss

Overland et al. 2016: Nonlinear Response of mid-latitude weather to the changing Arctic