Deep Ocean to Deep Space

AWSSI – Accumulated Winter Season Severity Index October 17, 2020

I watched this awesome presentation this week describing the AWSSI (awe-see) method of categorizing winter weather and taking some of the subjective personal variables out of it. Both the host for CoCoRahs, Henry Regis I believe, and Barb Bousted did an excellent job.

She got her inspiration from a PHD project she did trying to determine if the Long Winter described in Laura Engels Wilder’s book of that name was really that serve. The winter she describes was the one of 1880-81 and began for them on October 15. 

So began a project to measure and qualify winters by maximum and minimum temperatures, snowfall and depth. Of course there are other factors, such as wind, total precipitation of all kinds and cloudiness, but are not as widely collected as the parameters chosen are, historically. (I do wish we were doing a better job of that now. – dvg) 

When does winter begin?  It was decided that winter would begin on the first day that the high temperature was below 32 degrees F, or when there was more than 0.1″ of snow on the ground. Or December 1. It runs for the meteorological winter, December – February   unless extended by either cold or additional snow, or snow on the ground. And it is an index that accumulates, so you can check to see how bad this winter has been so far. 

Easiest to find the current data by searching on mrcc and awssi to find the page on the Midwestern Regional Climate Center website. There you can find maps for historical winters as well as how this current one is doing, and details on many sites where the data has been compiled.

 https://mrcc.illinois.edu/research/awssi/indexAwssi.jsp#info

I liked Barb’s take on snowfall amounts. “It’s like sausage, you don’t want to know what goes in it, but you love the results.” 

(Snowfall is tough, there are rules about how to collect it, but the real world never looks like that. And it takes humans to do it, no automated measurements. I do have an idea on how we might develop something but more on that another time.)

You can find this webinar on the CoCoRahs web site:

Description: Presenter: Barb BousteadNOAA/NWS’s Warning Decision Training Division, Norman, OKThis webinar will look at the Accumulated Winter Season Severity Index (AWSSI). AWSSI provides a scientific way to quantify the severity of a winter at any given location compared to its weather history. Using daily temperature, snowfall, and snow depth measurements, the AWSSI assigns a point total to each day of winter. Daily points add up through the winter season, giving a whole-season total at the end of winter. Besides the curiosity factor of having the numbers to support perceptions of whether a winter was severe or mild, AWSSI can be used to compare severity among sites or to compare the severity of one winter to others at a given site. The index can provide insight into wildlife and vegetation patterns, transportation and education impacts, and relationships between winter severity and other weather and climate patterns.