Alaska’s largest city surpassed seven feet of snow for the season with an exceptionally fluffy snowfall Sunday.

While the overall amount of snow in Anchorage is significant, weather watchers will tell you that the fluffiness matters, too. And how do they predict fluffiness? Well, that of course involves everybody’s favorite floating friend, the weather balloon.

That’s what National Weather Service climate researcher Brian Brettschneider tells us, back for our Ask a Climatologist segment.

First, though, Brettschneider says Anchorage’s snowfall is pushing into record territory.

Brian Brettschneider: We are up to, in Anchorage, 85 inches of snow for the season. Normally by this date, we would have 55 inches. So we’re two and a half feet above normal. And for this point in the season, we are in 5th place for the most snow through February 13. And that’s looking at basically about 100 years of snowfall data. So, you know, we’re top 5% right now.

Casey Grove: That’s interesting. We’re in the top five so far this winter, and it certainly could snow more here in Anchorage. It’s only the middle of February. So I think what was was really notable to people waking up this morning and seeing how much snow there was out there, as far as what it looks like covering, you know, the landscape, was how fluffy it was. Can you tell me more about that? I mean, how fluffy was the snow? I know there’s a measurement for this, right?

BB: Yeah, so there’s a term we use called the “snow-to-liquid” ratio. And that is, literally, if you melt the snow, how much liquid water do you get? And normally, in Anchorage, it’s about 12 to 14 to one. So every, maybe 12 or 14 inches of new snow — so not snow that’s already on the ground — new snow, if you were to melt that down, you would get about an inch of water. What we found with the snow that occurred on the 12th was, for a number of hours, it had a snow-to-liquid ratio of greater than 40 to one. So you would need at least 40 inches of that kind of fluffy snow to melt down into an inch of water.

You can imagine, you know, if you’re a weather forecaster, not only do you have to try to forecast how much moisture is going to come in, but then you also have to try to forecast how fluffy it’s going to be. And so if the thermodynamic profile of the atmosphere had been a little bit different, it might have only produced half the amount of snow or even less.

CG: What is the thermodynamic profile?

BB: It’s just like it sounds.

BB: No, it’s, you know, so in the atmosphere, you’ve got liquid water droplets. And even if it’s well below freezing, they’re in a liquid form. And when they come into contact with something, either another snowflake or a piece of dust or sea salt, it freezes. And the crystalline structure that it freezes into is highly dependent on the temperature that that occurs at. And there’s an optimal temperature in the atmosphere where you can make ice crystals that look like the kind you make in a Kindergarten art project, you know, where it’s got a bunch of little branches and arms. And that’s between minus 10 and minus 20 degrees Celsius, which is between 15 degrees Fahrenheit and a minus 5 degrees Fahrenheit. So that’s a real sweet spot temperature for making ice crystals that have these these kind of little arms. And then if you can keep that profile several thousand feet up in the atmosphere, because it’s got all these little arms, it’s a lot of little points of contact, that new little water droplets can stick to and crystallize on and create their own little branches.

So if you can have this part of the atmosphere that’s in this temperature range, and it’s fully saturated, you really can maximize the crystalline structure that that makes the most little branches. And what that does is it traps a lot of air, you know, between it. And so we think of fluffy snow, really, it’s snow that has a lot of air in between it. And so that’s really what we had yesterday, if you look at the the weather balloon that went up, it actually had a really very classic, perfect profile for what we call dendritic snow growth. You get the dendritic growth, it’s the little arms that are going off in all directions that can trap a lot of air.

CG: Yeah, fun to play in, too. And fun to talk about. And I think we’ve used this word in the past, but I’m gonna go ahead and say that it was “flufftastic.” Would you agree?

BB: I would. I’ll petition that to be put in the American Meteorological Society glossary.

CG: I would love that. Brian, you mentioned a weather balloon. And, you know, not to take too hard of a turn here, but balloons that travel through the atmosphere, high up, have been in the news lately, at least one of them confirmed to be a balloon. And so I thought maybe you could just remind us how does that work, these these friendly balloons, the ones that we like here, that the National Weather Service uses, what do they do?

BB: Yeah, so around the United States, there are, I believe, 92 locations where two weather balloons per day get launched. And around the world, It’s over 800 locations. And they’re synchronized so that they’re launched at midnight and noon Greenwich Mean Time, every day. So every place launches them at this same time. And that’s really important, because it gives us a snapshot of the atmosphere. So here on the ground, we have thermometers and anemometers. And, you know, we can record what’s going on here at the ground, but we really need to know what the atmosphere is like thousands, tens of thousands of feet up. It’s very important.

So in Alaska, we’ve got these 13 sites. And in the last few years, they’ve been transitioned to automated weather balloon launchers. So twice a day, either it’s scheduled or someone pushes a button, and it fills up a balloon, and it launches it. So it’s really quite a neat process. And one of the questions I get asked really the most is, “Wow, isn’t that a lot of pollution, you know, what happens if it falls in the ocean?” And they’ve really come a long way in how biodegradable they are. So there’s a few little metal parts in the middle of the instrument pack, but most of it is designed to be really quite biodegradable, and it, you know, basically disintegrates in a relatively short amount of time. Months to a year or two, I think.

CG: That’s interesting. I had wondered about that. I mean, especially if you’ve got all these sites that are launching two a day, every day.

BB: Yeah. And if you do the math, you know, at these 13 sites around the state, twice a day, 365 days a year, every day since 1948. You know, that’s tens of thousands of balloons.

CG: I mean, how else would you know if the snow was going to be fluffy or not?

BB: Well, so what we call the “Zero Z sounding,” so the one that was launched at 3 p.m. (Sunday), showed this perfect dendritic snow profile. The one that has was launched 12 hours earlier showed a very classic freezing drizzle profile. And that’s exactly what we had in the morning. And it was clearly evident in this upper air profile. So it really tells us a lot. And again, you know, that’s a key indicator of how much snow is going to fall. And so sometimes you’ll say the forecast is for two inches, but maybe four inches falls. And as a forecaster, you could have everything right, you could have everything nailed down, about the evolution of the storm, but a few thousand feet up, maybe it turns a degree or two cooler, and all of a sudden the snow gets fluffier. It may seem like a busted forecast, but just something as small as that can really make a big difference.

Casey Grove is the host of Alaska News Nightly and a general assignment reporter at Alaska Public Media with an emphasis on crime and courts.