GREENFIELD — With 2021 marking the wettest July on record in Massachusetts, followed by a severe drought in 2022, which was then followed by this year’s weekly deluges, one might be feeling a bit of “weather whiplash.”

New Englanders know their weather is unpredictable but going from 14 inches of rain two years ago to just 2.91 inches in last year’s drought back to another 14 inches of rain this year is far from normal for the region. In fact, prior to the last couple of years, the largest difference in rainfall in a two-year period was 9.88 inches in 2009 to 3.31 inches in 2010, according to data collected in Greenfield by the National Weather Service’s Cooperative Observer Program.

While scientists typically look at historical averages over long periods of time to examine a changing climate, these extreme shifts in weather variability each year may be a signal of climate change that the average person may observe, according to Jennifer Francis, a senior scientist at the Woodwell Climate Research Center in Falmouth.

“Climate scientists have long expected to see increased weather swings associated with a warming globe,” Francis wrote in an email. “Hot/dry spells are now hotter and drier, wet spells are bringing heavier downpours, and weather regimes of all sorts are expected to become more persistent.”

“Weather whiplash,” as Francis calls it, is the abrupt change in the weather after a long spell of different conditions and seems to be increasingly more common on a weekly, monthly or yearly scale. Day-to-day variability, however, has “generally decreased over time.”

National Oceanic and Atmospheric Administration extreme weather expert Dave Easterling said in an email that extreme weather events are becoming more common and scientists are examining if humans are having an impact on storm severity.

“There is always a ‘natural variability’ component along with a climate change component,” Easterling said. “The climate has already changed since pre-industrial times, so the question becomes how much of the severity of an event is natural variability and how much is climate change.”

Echoing that observation is Michael Rawlins, the associate director of the Climate System Research Center at the University of Massachusetts Amherst, who said the extreme weather events the Northeast U.S. has been seeing in recent years could be a manifestation of climate change. He cautioned, though, that a four-year stretch of extreme swings in precipitation are a weather trend, while climate trends are based on decades of data.

“Around the globe, this summer and in recent years, we’ve seen extreme precipitation events consistent with a warming climate,” Rawlins said. “Is that a trend that will continue? Time will tell.”

A variety of factors can play in the variable weather seen from year to year. Francis said a key aspect is the shifting of jet streams, which are the narrow bands of strong wind blowing west to east 30,000 feet up in the atmosphere. Other factors include abnormally warm ocean temperatures, early loss of spring snow and melting ice in the Arctic.

Francis explained the jet stream shifts, or “meanders,” north and south as it travels around the Earth, creating the highs and lows seen on TV weather maps. Weather patterns are typically sticking around longer due to the effect humans are having on the winds.

“Human-caused climate change is expected to make the jet stream take wide meanders more often, which causes weather systems to move more slowly and lead to long-duration weather conditions,” Francis said.

While western Massachusetts was drenched in July — Conway received 19.34 to 21.42 inches of rain, the highest reported rainfall for July in the country, according to the National Weather Service — the trend extended far beyond the Pioneer Valley, with several major weather stations reporting their record or near-record wettest Julys. The next highest July totals came from Northampton at 18.93 inches, Cornwall, Connecticut at 17.63 inches and Murray, Kentucky at 17.60 inches.

Hartford, Connecticut and Albany, New York saw the most July rain ever. Boston; Worcester; Providence, Rhode Island; and Williamsport, Pennsylvania had their second-wettest July on record, according to Cornell University’s Northeast Regional Climate Center.

Rawlins, emphasizing his expertise is on climate, not weather variability, said dramatic swings between “wet and dry is consistent with an intensification of the hydrological cycle,” the process by which water circulates around the planet. This means periods of low precipitation and high temperatures lend themselves to drought, while wet periods bring on deluges.

“An intensification of the hydrological cycle is most certainly simulated in models and that’s what we’re experiencing,” Rawlins said. “Wet areas of the globe are projected to get wetter and dry areas are predicted to get dryer.”

As for August? Keep the umbrella handy as the National Oceanic and Atmospheric Administration’s monthly precipitation outlook is projecting an above-normal amount of rain.

Chris Larabee can be reached at clarabee@recorder.com or 413-930-4081.

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