By Jacob Jenkins, science & technology reporter
Last week, the United States experienced a significant winter weather event that stretched from New Mexico to the far corners of Maine. Forecasts saw conditions such as consistent heavy snow, freezing rain, and harsh temperatures across more than 30 states.
While the U.S. is no stranger to powerful winter storms, questions have been raised regarding the nature of the storm and how it developed. The sheer size and reach were without a doubt anomalous characteristics. Areas that hadn’t experienced such fierce weather in 3-4 years, such as Blacksburg, VA, were met with dangerous conditions that have lingered since. The storm also managed to travel across the entire country, forming in the Pacific Ocean and making its way across the Midwest to the East Coast.
Dr. Andrew Ellis, a Virginia Tech professor and director of graduate studies in the department of geography, gave an in-depth look at the science behind Storm Fern and whether or not its conditions could be deemed unnatural. His background as a hydro-climate scientist brought great insight to what factors allowed the storm to develop, how it maintained strength during its course, and how its harsh conditions arose.
(Edited for clarity)
What was your first reaction to the storm?
Impressive aerial coverage. That was fairly unprecedented in terms of the length of the storm. We haven’t had many storms in recent years that have come out of the Southwest and all the way across the southern tier and up the east coast of the US.
What factors came into play regarding how the storm stretched so far and how it became so large?
This winter, we’ve had little storm systems that have been associated with the northern jet stream, which is basically dropping out of Canada. We haven’t had much interaction from what’s called the subtropical jet stream, which is more of a Southern Tier coming in off the Pacific Ocean. This was really the first instance where the subtropical southern jet stream got involved. Usually, that jet stream brings the moisture, and the northern jet stream brings the cold. We’ve had cold but not a lot of moisture. This one brought a heck of a lot of moisture. The subtropical jet, the wet jet from the south, is really what made this one more unique than what we’ve been dealing with, not just this winter, but in recent years.
Did climate change have any impact on the storm?
Probably not this one. These things have been happening like this for as long as we’ve been looking at records. In fact, it’s been less frequent here in the last few years. The climate change angle probably has more to do with the cold that was associated with this one, which sounds counterintuitive, right? Global warming and cold outbreaks. That northern jet that we were talking about, it gets a little bit more wavy with global warming, and so it can sort of drop farther south at times and bring cold air into places that don’t necessarily typically experience that.
Arctic amplification, the rapid warming up at the Arctic region of the Northern Hemisphere, has caused the jet to be a little weaker. That weakness of the jet, less strong winds, has caused it to sort of meander a little bit more. When it meanders it can drop south and that’s when the cold air comes into play. Back in the 1970s really strong jet cold air tended to stay bottled up more to the north. But here, in recent years, we get these episodes of cold air outbreaks when the jet weekends and drops South from time to time. You could make the argument that the warming climate change has played a role in the temperature, at least at the surface.
How often do these powerful winter storms occur?
In recent years, it hasn’t been the case. It’s probably been four or five years since we’ve had a really strong east coast storm like that. Traditionally, a handful, two or three of these a year, would be fairly typical up until the recent period.
In Blacksburg, we saw heavy snow, sleet, and ice. How did we get such a variety in the forecast?
The amount of cold that we had at the surface was a bit unusual. The models started to move the storm more northwest, and so we were on the warm side of the storm, drawing warm air up from the south. Once you start to inject some warm air in the middle part of the atmosphere, the snowflakes on their way down melt. If they completely melt, when you’ve got some really warm air in the middle part of the atmosphere, then it remains liquid all the way down until it hits the cold surface and freezes as freezing rain.
The warm air aloft was really indicative of a pronounced freezing rain event. The forecast here was pretty dire, with half inch accumulation of ice, if not more, which would have been crippling. The cold air really hung in there for us, and kind of held most of the warm air to the south and didn’t let it get in here and totally turned it over to a freezing rain event, which is great.
Could you go into more detail on Blacksburg’s icy conditions?
What’s on the ground is like a block of ice. It’s like concrete. That’s because of the prolonged period of sleet events that we experienced, which was really rare. But I think the biggest issue too is we had an inch and a quarter of water equivalent. There was a ton of water in this little, tiny snow and ice pack that we have out there, so it’s not surprising that it’s like concrete.
Is there anything you’d like to add?
Looking ahead it does not look as extreme cold as we’ve had, but the pattern is still on the cold side. Anytime you’ve got the northern jet dropping down and bringing cold air, there’s always chances for little storms to spin up on the periphery. I don’t think we are heading into a totally snow free period for the next few weeks. I think we’ve got some more interesting weather on the horizon.
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