How Do You Read a Heavy Snow Risk Map?
A heavy snow risk map shows where forecasters see a chance of conditions meeting a defined snow-hazard threshold during a specified period. To read it, start with the product name, valid dates and legend. A shaded region on the Climate Prediction Center’s week-two outlook identifies a potential hazard eight to fourteen days ahead. It does not give every town inside the outline a promised snowfall total. The useful question is what event the shading describes, and how likely that event is. The probability belongs to a threshold. CPC’s product description explains that its probabilistic hazard maps use slight, moderate and high risk categories associated with probabilities exceeding 20, 40 and 60 percent. These are chances of exceeding the hazard threshold. They are not percentages of a state that will be buried, or percentages of the week during which snow will fall. A higher category expresses greater confidence in that defined outcome; it does not, by itself, mean a deeper accumulat...
