Our first winter storm of the season impacted a majority of the state this weekend. For days leading up to the arrival of the winter storm, there was a lot of speculation of just what type of winter precipitation would fall and where it would land.
Even just three days in advance of the event, many meteorologists were hesitant to publish forecasted snow totals. Initial snow accumulation forecasts were very broad, and they had wide ranges from just a few inches of accumulation to nearly a foot in some locations in the far northeastern part of Missouri.
Fluctuationing forecasts such as the ones we saw before the weekend winter storm are more common in the winter, as wintry precipitation can be difficult to predict due to a variety of factors.
Predicting precipitation relies heavily on the vertical temperature profile of the air. While the air at the surface influences precipitation accumulation, any temperature change that rain, snow or ice pellets encounter on the way from a cloud to the ground can alter what type of precipitation will reach the ground. Because of this, knowing the air temperatures from the ground to the height of the clouds is important. Many times, this information is difficult to pinpoint until the storm system is over land. Often, this means that data is not clear about things like temperature and storm movement until just a few days before the system influences Missouri's weather.
As the amount of time decreases before a weather system impacts an area, the amount of available information about that system increases. Real-time data from the system as it approaches the Show-Me State can be compared to previous model prediction of what the system would be doing at the same time and location. This allows meteorologists to check the model output with what actually is occurring in other locations. If a certain model has handled the forecast for a storm better than another, it may be a sign to rely on that model rather than a different one.
Because winter weather forecasting is so detailed to begin with and a difference of a few degrees can change the precipitation outcome, many meteorologists will not put out a specific forecast until a day or two before the event. Instead, they will communicate the probabilities for each possible outcome, including the precipitation types and potential high end and low end accumulation amounts. These forecasts will generally become more detailed as better model guidance and more reliable data become available.
Maddie Fennewald has worked as a broadcast meteorologist and marine meteorologist since graduating from the University of Missouri in 2021. She has worked with the Missouri Climate Center and conducted research on atmospheric blocking while at MU.