Ever since 2014, you’ve heard in national news. “The Polar Vortex is set to bring record cold next week!” But what is it exactly, and is it a new phenomenon? The answer to the latter question is no. The polar vortex has been documented as early as the mid-1800s and is a naturally occurring ‘blob’ of low pressure that rotates around the North Pole each winter. The polar vortex meteorologists specifically refer to is in the stratosphere, which is located roughly 10-30 miles above the surface of the earth.

So how can something so high up in the atmosphere over the North Pole influence our weather? When the polar vortex is strong, it keeps the cold well north of our region as powerful jet stream winds blow west to east over the Arctic. However, when waves in the atmosphere trigger warming in the stratosphere, the polar vortex can become disrupted and displace cold air further south. Notable stratospheric warming events such as in January 2015 have been responsible for brutally cold months to follow in the northeast United States.

As important as the polar vortex can be for our temperature, it can also play a factor with snow. A sudden stratospheric warming event occurred at the end of January 2010, which arranged the northern hemispheric pattern so that cold and snow were locked into Pennsylvania for much of February. It ended up being Harrisburg’s snowiest month on record.

Not every stratospheric warming event leads to frigid cold and snow outbreaks for us, but the more frequent and intense these events are, the greater the probability for disruptive winter weather in the eastern US. Last winter, the polar vortex was in one of its strongest states on record, which lead to the record warm and uneventful winter for us as most of the cold air remained bottled north.

The ‘Arctic Oscillation’ is a good index to use when analyzing the current and future state of the Polar Vortex. A positive AO is synonymous to a strong polar vortex and is unfavorable for severe winter weather in the eastern US. A negative AO is just the opposite and can foreshadow potential cold and snow outbreaks. A good place to find this information is here: https://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.shtml

2021 Weather Almanac