Certain types can bring large areas of land to a standstill, with the potential for power outages, impassable roads, icy conditions, power outages and collapsing roofs.
It is critical that forecasters try their best to get it right.
There are three basic types of winter precipitation: snow, sleet and sleet. The kind of precipitation you will get is all based on the air temperature at different levels of the atmosphere.
Think of the atmosphere as a tall column. If that column of air is below freezing from top to bottom, the result is snow.
If there is warm air at the top and freezing temperatures towards the bottom of the column, then you have wet snow. This is because the warm air high in the atmosphere will produce a raindrop. If the raindrop falls and enters the air below freezing, it will freeze before hitting the surface. Since freezing rain is basically a frozen raindrop, you can really hear black ice when it hits the surface.
Finally, if the entire column of air is above freezing to the surface, the raindrop will freeze on contact. This is called freezing rain and it is the most dangerous form of precipitation.
“Some of the most disastrous winter weather storms are mainly due to freezing rain,” says the National Weather Service.
Freezing rain freezes everything it comes into contact with, creating a dangerous glaze of ice on roads, trees, power lines and your vehicle. The weight of the ice can topple trees and power lines, causing power outages during extremely cold temperatures.
The ice on the roads turns the roads into ice rinks and can cause major traffic accidents and interstate congestion.
It takes less than half an inch of ice to make travel dangerous. Tree branches start to break with a quarter to a half inch of ice buildup. And when more than half an inch of ice builds up, there will be widespread tree damage and extensive power outages.
The importance of being right
Deciding where the rain stops and the snow starts can make all the difference in where to deploy de-icing machines, airplanes, school cancellations and more. It is also incredibly important to know which areas will get sleet or sleet.
The rain-snow line is a term we often hear when a winter storm is predicted. The term simply defines the point at which the rain turns to snow. In mountainous areas it takes on a vertical connotation and is determined by the height at which rain turns into snow.
If the rain-snow line is predicted inaccurately, it could mean that a city expects to get all the rain from a storm and eventually get all the snow. This can have devastating consequences if a city has no plans for snow and has not treated the roads, canceled schools or warned residents.
The same can also be true if a city expects all the snow and eventually gets all the rain. They would have wasted countless taxpayer dollars dealing with roads and business closures in preparation, and then nothing happens.
Most people living in the south can remember a “snow day” when no snow fell. Important decisions, such as school closures, must be made during the nighttime period when winter rainfall is expected in the morning hours. If the temperature is a little warmer than expected, that winter precipitation will fall as rain and you will have a failed forecast.
For example, it is essential to know the height of the rain-snow line in Colorado to know if some mountain passes along Interstate 70 can remain open. In New York, knowing whether the rain-snow line will reach the I-95 corridor or continue westward is crucial.
Why do bridges freeze first?
During winter weather, bridges and viaducts are the first to freeze. This is because they have air on all sides, so they will cool faster than surface roads. Overhead roads are naturally more isolated because the cold air is only above the ground, while the underground keeps the roadway warmer.
Then you have a so-called winter mix. It’s actually a little bit of everything. When you are near the rain-snow line, the rain can turn to sleet over time and then turn to snow. Or snow turns into rain.
Forecasters have the important task of not only determining what type of precipitation will fall, but also timing when one type of winter precipitation changes to another.
It is crucial to know what time rain turns to snow. Will it happen before or after the commute?
Undoubtedly, it is challenging and not always perfect. But knowing what will fall and when is key to staying prepared in winter weather.
CNN meteorologist Taylor Ward contributed to this report.