As I write this article we are in the midst of receiving only our third healthy dose of snowfall accumulation for the season as snow (in large amounts) has been hard to come by so far this winter. So I figured this would be the perfect opportunity to explain one of the bigger weather “headaches” that meteorologists face when it comes time to forecast snowfall amounts.
When you reach your senior year as a meteorology student you begin to put all of the pieces of the weather “puzzle” you learned together, which include several principles involving physics and calculus, both subjects that would make anyone cringe, but it sure does help explain why making a snowfall forecast is so difficult and most often times a frustrating endeavor. It is quite amazing how many processes are involved when it comes to producing precipitation whether it be rain or snow and how each process interacts with another.
When it comes to snowfall forecasting, there are several important variables at play. For starters you have the state of the atmosphere just above our heads here at the surface where we look variables like temperature, moisture, and winds. Twice a day weather balloons are launched from the Davenport, IA and other National Weather Service offices around the country. These balloons paint a picture of what is happening just above us here at the surface, giving us important data on temperature, wind, pressure, moisture and a multitude of other important data points. Data from these observations then gets fed into the supercomputers that produce the weather models forecasters use to create forecasts. Unfortunately, we only get two of these per day (unless a major storm is forecast in which a special reading is often taken) so this complicates things and often causes forecasts to change drastically even up to 24 hours before storm impacts are felt.
While model resolution continues to improve, even with the increased resolution it all begins with the data that is being fed to the models. The more data we can provide the better the models will perform.
Storm track is another important factor when forecasting snowfall, as we typically see the heaviest accumulations on the northern fringes of the storm track where the cold air resides. How much cold air and how much moisture is in place adds yet another variable, and often times the models won’t agree with where these places exist.
So the next time you find yourself scrolling through your Facebook feed or clicking through the local TV stations and happen to notice varying snowfall forecast amounts and locations, you’ll have just a small taste of why winter storm forecasting can be so variable at times even with the best technology available.
