May 29, 2015
Are you noticing anything different about the weather this spring? Kate from Pittsburgh says she is. She posted a comment recently on iSeeChange.org—a community conversation about weather and climate.
Kate describes the last week as “yo-yo weather.”
“There was a frost advisory for the morning of May 23 with a low 14 degrees below normal. But the high was exactly normal. Now May 24 is predicted to be 5 degrees ABOVE normal. This is much more variability than I remember in the past.”
So what gives? We got in touch with some scientists from Penn State University’s meteorology department to find out if what Kate’s reporting is normal.
Fred Gadomski, a meteorologist and host of the Weather World broadcast on the Pennsylvania Cable Network, says “normal isn’t really normal when it comes to the weather.” He says “normal” temperatures are just averages of all of the weather for a particular place on a particular day over the last 30 years or so—including these large variations, which are not uncommon in spring.
Meteorologists say the big temperature swings we’ve been experiencing are a result of our region currently being in a “high amplitude pattern.” In a nutshell, this means that the jet stream, which on average flows from west to east, has unusually large bends in it. That brings cold air masses south and unusually warm air masses farther north than usual.
This pattern can create frost one day and temperatures that feel like summer the next. Gadomski says we’ve been in this pattern for a few weeks, and it might last a couple more. But no weather pattern lasts forever.
David Titley, Director of Penn State’s Center for Solutions to Weather and Climate Risk, also says it’s important to remember that weather isn’t climate. Titley says meteorologists look at climate as a longer-term average.
“Let’s say you’re playing poker. And you’ve got five cards in your hand. Think of those five cards. They may be really good cards, they may be bad cards, they may be something in the middle. That’s weather. That’s like today’s weather. Climate is the card deck from which that got dealt.”
And climate change? That’s like “slipping a couple more aces into that deck,” Titley says. “It changes the odds of getting extreme weather events.”
Titley says, in Pennsylvania, the averages for nighttime and daytime temperatures are creeping up. But change in temperature variability is something they are still trying to figure out. His center is working on what he calls a “weather weirdness index," which would quantify how the jet stream is changing. That would help him better answer questions like Kate’s.
So Kate—thanks for posting to iSeeChange.
If you have a weather or climate-related observation or question, go to iSeeChange.org, login, and tell us about it. You can upload photos or videos too. We can’t wait to hear what you’re seeing, hearing or feeling.