Given this week’s record blizzard in the Midwest—so far it’s the third largest snowfall in Chicago on record–I was curious about whether there is bias in predicting the amount of snowfall. In other words, do forecasts tend to overpredict the amount of snowfall? And if so, do we catch on and underprepare for snowstorms?
I found a paper by Bruce Rose from the Weather Channel (with Joseph Koval and Eric Floehr) that answers this question. They report that for a small set of snowstorms from 2007-08, there is an inverse relationship between the intensity of a snowstorm and the reported level of over-prediction, meaning that lighter storms are more exaggerated while heavier storms are less exaggerated. While they could not confirm the findings for a larger data set from the Weather Channel’s database, they write that there is a “marked tendency to over‐predict light events, but this trend is reversed with moderate and heavy snowfalls.” This seems to be consistent with what I have observed in Virginia, where there is much ado about virtually no snowfall.
As for whether people over-prepare or under-prepare for storms, I’ll have to answer that another day.