Blizzards are a subcategory of snowstorms. The National Weather Service (NWS) lists four criteria a snowstorm must satisfy before it reaches “blizzard” status:
1. Significant snowfall.
2. Sustained winds blowing at 35 mph minimum.
3. Visibility is limited to a quarter-mile or less.
4. All of the above conditions must persist for a minimum of three hours.
This article is the fifth in a series of charts providing information on tornadoes, hurricanes, wildfires, earthquakes, blizzards, and volcanoes
Measuring Blizzards
Similar to wildfires, there is no specific scale for measuring the intensity of a blizzard. In this article, we reference two different scales that measure specific components of blizzards: snowfall and ice accumulation. Snowfall is measured on the Regional Snowfall Index (RSI), which accounts for the physical location of a blizzard, the number of people living in that area, and the amount of actual snowfall. Ice accumulation and the potential damage it could cause are measured according to the Sperry-Piltz Index (SPI) using the temperatures during a snowstorm, wind speed and direction, and the total precipitation, which may need to be converted into ice accumulation.
On both the RSI and the SPI, a higher category indicates a more severe blizzard. Though the occurrence of a higher classification of storm is rare, they do occur.