The week of Halloween was absolutely frigid. Halloween night itself had a “high” as low as 43 degrees, with trick or treaters even surprised by intermittent flurries of snow! For context, the last time it snowed on Halloween in Ohio was in 1993, exactly 30 years ago. Obviously, something is up with the weather, and this sudden cold snap has left many Ohioans wondering what exactly the cause could be. Luckily, a couple of well-defined factors seemed to be the culprits here, leaving no air of mystery.
Foremost, we have a common source of chills all around the Midwest: Canadian winds. These frigid winds are pushed down towards the Midwest due to a phenomenon known as the Arctic Oscillation. The Arctic Oscillation (AO for short) essentially is shifts of pressure between the Arctic and the mid-latitudes of the North Pacific and Atlantic. The AO is split into two phases: its positive phase, and its negative phase. The AO’s positive phase has the Arctic experience lower-than-average air pressure, while the Pacific/Atlantic oceans experience higher-than-average air pressure. The negative phase sees the inverse occur. Specifically during the negative phase, the mid-latitude jet stream is shifted more towards the equator, and therefore south. As a result, Arctic winds from the north sweep down towards the mid-latitudes, bringing frigid temperatures along with them. So, what does all of this mean for Ohioans? The effect of the AO is felt most heavily in the northeastern end of Ohio, though its effects can’t be discounted elsewhere. Here in the south, the AO’s interference brings overall colder temperatures and a greater chance of snowfall. Because southern Ohio lacks influences from other external elements (such as the Great Lakes, which mostly affect northern Ohio), the effects are, thankfully, not nearly as bad as they could be.
However, the effects of the AO are exacerbated when paired with the second phenomena: El Nino. El Nino and its counterpart, La Nina, are climate patterns that break the Pacific Ocean’s typical pattern of upwelling. Upwelling is the rise of cold water to replace warm water pushed away by trade winds. El Nino and La Nina are known as the El Nino-Southern Oscillation Cycle (ENSO). During El Nino, warm waters are pushed towards the west coast of the Americas due to weakened trade winds. This leads the Pacific to become unusually warm, which then affects the Pacific jet stream. The jet stream is shifted south, leading to a slew of effects all over the Americas. In the Midwest, El Nino usually means a drier and warmer summer. However, due to El Nino potentially leading to a more active storm track across the southern United States, the Midwest could possibly see an increase in precipitation and heavy snow events.
The AO and El Nino end up having a sort of synergy, despite one thinking they’d cancel each other out, in a way. This synergy seemed to peak in late October of this year, hence the sudden drop in temperature and surprise appearance of flurries. However, this dynamic duo is expected to keep causing issues all the way into the new year, with Ohio forecasted to have a heavy amount of snowfall. Make sure to stay warm, and cross your fingers for a white Christmas!