The devil is in the details: When the forecast is very good, but the results are very bad!

There are times when what would otherwise be considered a very good forecast can result in a perceived “bust” by the public. Some meteorological situations involve much tighter tolerances for various parameters – QPF and temperature forecasts – than do others. These situations also highlight the need to discuss the issue of forecast uncertainty and the impacts of various forecast scenarios. Additionally, our understanding of and ability to evaluate and quantify certain physical processes can determine how we “sell” our forecasts – and especially their impacts – to the public. To highlight these issues and the dilemmas they present the broadcast meteorologist, we examine three cases in central North Carolina.

The first case is the infamous “Raleigh gridlock” storm of January 19, 2005, where a forecast of flurries off by 0.04” of liquid equivalent resulted in a paralyzed city in a classic “low intensity, high impact” event complicated by a lack of understanding of the interaction between a light, powdery snow; very cold road surfaces; and heavy traffic.

We present the second and third cases as a compare and contrast of a “low intensity, high impact” situation with a “high intensity, low impact” event. The former is a well-forecast case of light freezing rain and the dozens of accidents caused as a result. The latter not only involved the uncertainty and tighter tolerances of a classic “Miller-A” winter storm in the Carolinas but also the inability to quantify in real-time various physical processes affecting the accumulation (or lack thereof) of falling snow as well as whether the resulting accumulations of snow and slush would freeze or evaporate in very dry surface winds.

We conclude with some suggestions how we can better communicate the degree of uncertainty in our forecasts as well as the uncertainty in the resulting impacts, since that uncertainty can be the difference between a weather event your viewers talk about for years and one that just induces more nasty e-mails!