For Ohio University students celebrating Halloween weekend, one thing stood out: the cold weather. Temperatures dropped below freezing several nights in a row.

“Halloween is fun, but if you’re freezing the whole time, you’re just not going to be having that much fun,” Sam Archer, a sophomore studying civil engineering, said.

The drop led to students being especially careful about the costumes they chose.

“Some of my friends, I know for sure, contemplated the outfits they were going to wear,” Braden Young, a sophomore studying mechanical engineering, said.

Nevertheless, others were less affected by the cold.

“Obviously, it was late, it was cold, but I wouldn’t say it really affected it in a negative way,” Luke Risko, a sophomore studying mechanical engineering, said.

Ryan Fogt, the director of the Scalia Lab, OU’s official weather forecasting service, said the cold snap was the result of a shift in the jet stream.

“The last few days with the highs in the lower 50s have been below average,” Fogt said. “Normally, they’d be close to 60.”

That change was caused by a southward dip in the jet stream, a fast-moving air current that influences temperature patterns across the U.S.

“When the jet stream dips farther south, and we are in the north side of the jet stream, we’ll be in colder air,” Fogt said. “We’ll have more intrusions of cold air from the Arctic, maybe, or even just from Canada, and that tends to make the temperatures much colder.”

When the jet stream moves north, the opposite occurs.

“If the jet stream is farther north, we’re going to get more of the tropical air from around Florida and the Gulf, and that’ll make temperatures warmer,” Fogt said. “Right now, we’re kind of in transition season between those two things, so the jet stream is variable.”

This week, the jet stream will move north, leading to a return to normal conditions, followed by much warmer temperatures.

“The forecast for the next week at least, is for temperatures to moderate again and to turn to near normal, and then maybe even by midweek, to be above normal, up in the 60s, which for November is not normal,” Fogt said.

The jet stream’s northern position earlier this fall also contributed to a local drought that stretched from August into early October.

“High pressure tends to lead to clear skies, less precipitation,” Fogt said. “It steers storms away from our region, so they tend to divert and go around us rather than toward us, and that leads to a deficit in precipitation if it occurs for a long period of time and can lead to a drought if it’s persistent.”

That extended warmth was also responsible for the delay in fall foliage, with leaves still being seen on trees into November.

“Because it was warm throughout much of September and early October, the leaves didn’t turn,” Fogt said. “It really requires colder overnight temperatures for them to want to start losing chlorophyll and turning.”

Fogt said the broader weather trends reflect the long-term effects of climate change, which is gradually warming and drying Ohio’s climate.

“The overall pattern of climate change is a warming signal and a drying signal, longer periods between rains, and then when we do have rains, they’re heavier and more rain at a time,” Fogt said. “Most of the rains that we’ve had, even from June and July up to now, are heavy rains, where we get more than an inch of rain at a time.”

ap007223@ohio.edu