Unlocking the Secrets of Predicting Mixed Precipitation: Your Guide to Winter Weather Insights

CEDAR RAPIDS, Iowa — Forecasting weather can feel like solving a puzzle with too many missing pieces. It’s especially tricky during winter. Meteorologists find this season challenging because small changes in temperature can shift rain to snow or freezing rain.

In Cedar Rapids, we can have extreme temperature swings—from -30°F to nearly 80°F—in just a few weeks. A difference of just a few degrees can entirely change what kind of precipitation falls. Why is this so important?

It all starts with what’s happening in the clouds. When temperatures drop below 14°F, about half of the cloud is likely made of ice crystals. If it’s too warm, the precipitation may not freeze properly, leading to rain instead of snow. To get snow, we need colder temperatures at various heights in the atmosphere, not just at ground level.

If the air is warm enough throughout the lower 5000 feet (above 37°F), we might just see rain, even if it’s cold at the surface. On the flip side, if it’s mostly below freezing, snow is more likely.

Freezing rain adds another layer of complexity. It often happens when the clouds are warm, but colder air at the surface causes the rain to freeze on contact. If that freezing layer is less than 2000 feet high, the rain doesn’t have enough time to turn into solid ice before hitting the cold ground.

However, if the freezing layer is deeper than 2000 feet, the raindrops freeze completely before reaching the ground, forming sleet—or small, firm ice pellets. Sometimes, we get graupel, which are softer and more fragile ice pellets formed when supercooled water droplets freeze on existing ice or snow. Sleet appears clearer and smoother, while graupel is often opaque and rough due to the snow it forms around.

Weather forecasting isn’t just about understanding these processes; it involves complicated models and various methods. Each model has its own rules and variables, making it tough to predict mixed precipitation accurately. Meteorologists and researchers are always looking for ways to improve predictions, especially for tricky weather events.

If you’re interested in digging deeper into how meteorologists forecast different types of precipitation, check out resources from the National Weather Service for more detailed information!