Winter seasons have significant societal impacts across all sectors ranging from direct human health and mortality to commerce, transportation, and education. The question “How severe was this winter?” does not have a simple answer. At the very least, the severity of a winter is related to the intensity and persistence of cold weather, the amount of snow, and the amount and persistence of snow on the ground. The Accumulated Winter Season Index (AWSSI) was developed to objectively quantify and describe the relative severity of the winter season.
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The AWSSI is not limited to meteorological winter (December ‐ February) but is intended to capture winter weather from its earliest occurrence to its last. The winter season begins when the first of any one of the following instances occurs:
First measurable snowfall (>= 0.1 inch)
• Maximum temperature at or below 32°F
• December 1
The winter season ends at the last occurrence of any of the following:
• Last measurable snowfall (>= 0.1 inch)
• Last day with 1 inch of snow on the ground
• Last day with a maximum temperature of 32°F or lower
• February 28/29
Daily scores are calculated based on scores assigned to temperature, snowfall, and snow depth thresholds. The daily scores are accumulated through the winter season, allowing a running total of winter severity in the midst of a season as well as a final, cumulative value characterizing the full season. Accumulations of the temperature and snow components of the index are computed separately and then added together for the total index. This allows comparison of the relative contribution of each to the total score.
The AWSSI has been processed for 52 locations across the continental U.S. to provide a variety of locations in different climate regimes for analysis. The AWSSI is calculated for each season from 1950‐1951 to 2012‐2013. The seasonal data is then subject to quality control, and seasons missing data that would contribute 5% or more of the seasons AWSSI are removed . Averages and standard deviations are calculated for running accumulations of daily temperature and snowscores as well as the total AWSSI.
Quintiles of AWSSI scores were determined for each location. Descriptive categories were assigned to each quintile as follows:
The Accumulated Winter Season Severity Index (AWSSI)
Barbara E. Mayes Boustead, Steven D. Hilberg, Martha D. Shulski, and Kenneth G. Hubbard. Journal of Applied Meteorology and Climatology, Vol. 54, No. 8, August 2015: 1693-1712.
Abstract | Full Text | PDF (2545 KB)
An Accumulated Winter Season Severity Index. Barbara Mayes Boustead, NOAA/NWS, Valley, NE; and S. Hilberg, M. D. Shulski, and K. G. Hubbard. Presented at 93rd Annual Meeting of the American Meteorological Society, January 2013.
An Accumulated Winter Season Severity Index (AWSSI). Webinar for the NWS Central Region, February 2017.