Steve Hilberg, the senior climatologist/meteorologist for the Midwestern Regional Climate Center at the University of Illinois, and a collaborator, Barbara Mayes Bousted, a meteorologist with the National Weather Service, have developed a new way to historically compare winter severity by using local weather data. Hilberg was interviewed recently by News Bureau editor Mike Helenthal.
Locally and nationally, how does the last decade fare on your index?
The index (Accumulated Winter Season Severity Index – AWSSI) not only lets us look back historically but also allows us to monitor the current season. Over the last decade we have seen a lot of variation, but certainly more moderate winters. The winter of 2011-2012 was one of the tamest on record (since 1950). Of course, this year we are dealing with one of the top five most severe winters across much of the central U.S., according to the index. The last time many locations experienced a winter this severe was in the late 1970s and early 1980s.
What is making this winter season seem so comparatively severe for the eastern half of the United States?
We have changed the definition of the “winter” season for the purposes of the index to take into account winter weather that occurs in, say, November, or in March or April. Without getting into too much detail, it more closely coincides with the snow season (that is, the first snow to the last snow). The severity of this winter has been a combination of both extreme cold and much above average snowfall, but the contribution of each varies depending on where you are. Here in the central U.S., the cold weather has been more dominant, although snow has also been a heavy contributor. For New York and Philadelphia, even though it has been colder than normal, the extreme snow has been a major contributor to the severe winter there.
What does your index measure and how is it similar to, or different from, other weather indexes?
We use the daily maximum and minimum temperatures, snowfall and snow depth for each day. Each of these parameters receives a score depending on the value, and the scores are totaled for the day. The daily scores are then added to get the AWSSI. We use these four measurements because they are commonly measured and available.
What winter weather variables are not included in the index?
We do not take into account wind or wind chill. Wind measurements are not available for most locations, so accounting for wind chill would be difficult. We also do not take into account freezing rain (glaze) because there is no routine reporting of measurements of ice thickness on a daily basis.
Is the index being used elsewhere?
The AWSSI is still in development and is not being routinely used yet. It just has happened to have garnered a lot of interest because of the severity of this winter. When we complete development and associated studies, we hope it will be widely used.
You talk about winter with a certain glee and no doubt root for the groundhog to cast a long shadow. What is it about winter that you enjoy?
I do enjoy winter in general, in particular snow and snowstorms. However, I’m not a fan of freezing rain (too damaging, messy and potentially paralyzing) and I can do without subzero wind chill. I know winter can be a big pain for a lot of folks (including me at times), but it’s going to happen, so I try to enjoy it while it’s here. Like most people, by March, I’m ready to look ahead to the warmer weather of spring.
