Many Utah gardeners were caught off guard last week when frost burned tomato plants they’d just put in the ground. But a new scientific paper from the University of Utah helps explain why that unexpected frost really isn’t so surprising.
Climate scientist Court Strong scrambled last week to drape plastic over his family’s backyard tomato plants. The rule of thumb locally is that it’s pretty safe to plant by Mothers’ Day weekend.
But not this spring.
“So, this is the plastic I bought to make the greenhouse,” says Strong, an associate professor in the University of Utah’s atmospheric science department.
The frost-free season is 10 days longer now than it was a century ago, and it’s natural to think that’s because of climate change. But, in a recent scientific paper, Strong and a scientist from the U.S. Geological Survey identified atmospheric circulation as a bigger factor in late frosts than climate change.
“Even though global warming affects the timing of fronts because it affects circulation,” he says, “most of the variability we’ve seen over the last century is really due to changes in wind direction more than it’s due to large-scale warming.”
The study is published in the scientific journal, Nature Communication. And, in it, the researchers traced the timing of most frosts to thunderstorms in the Pacific Ocean near the Equator.
“What’s interesting about the study is understanding where [the frost trend] comes from,” he says.
This is not the first scientific data linking Pacific weather patterns to Utah’s skies. Utah State University scientists have found those patterns affect winter pollution episodes here.
As for Strong, he says his study probably won’t help much in forecasting late frosts -- Pacific weather is too unpredictable. So, he’ll keep the plastic handy for future tomato starts.