Certain types can paralyze large parts of the country, with the potential for whiteout conditions, impassable roads, icy conditions, power outages and roof drops.
It is crucial that analysts do their best to get it right.
There are three basic types of winter precipitation: snow, hail and freezing rain. The type of precipitation you get is based on the temperature of the air at different levels of the atmosphere.
Think of the atmosphere as a tall column. If that column of air is below zero from top to bottom, the result will be snow.
If there is hot air at the top and temperatures below zero at the bottom of the column, you will experience hail. This is because the hot air at the top of the atmosphere will produce a raindrop. As the raindrop falls and enters the air below zero, it freezes before it reaches the surface. Since snow is basically a frozen raindrop, you can hear the snow when it hits the surface.
Finally, if the entire air column is above the freezing point to the surface, the raindrop will freeze on contact. This is called freezing rain and is the most dangerous type of precipitation.
“Some of the most disastrous winter storms are mainly due to freezing rain,” said the National Weather Service.
Freezing rain freezes anything it comes in contact with, causing a dangerous layer of ice on roads, trees, power cables and your vehicle. The weight of ice can knock down trees and power lines, causing power outages during extremely low temperatures.
Ice on the roads turns them into ice skating rinks and can cause serious traffic accidents and interstate blocking.
It takes less than half an inch of ice to make the trip dangerous. The branches of the trees begin to break with an accumulation of a quarter to a half inch of ice. And when more than half an inch of ice accumulates, there will be widespread damage to the trees and major outages.
The importance of being right
Deciding where the rain ends and the snow starts can mean the difference in where to employ de-icing machines, aircraft de-icing, school cancellations and more. In addition, knowing which areas will receive hail or freezing rain is extremely important.
The rain-snow line is a term we often hear when a winter storm is forecast. The term simply defines the point at which rain changes to snow. In mountainous regions, it takes on a vertical connotation and is defined by the altitude at which rain transits to snow.
If the forecast of the rain and snow line is inaccurate, it could mean that a city expects to receive all the rain from a storm and, in fact, ends up receiving all the snow. This can have devastating consequences if a city does not plan for snow and does not treat roads, cancel schools or alert its residents.
The same can also be true if a city expects to receive all the snow and ends up receiving all the rain. They would have spent countless taxpayer dollars dealing with roads and closing deals in preparation, and then nothing happens.
Most people living in the south can remember a “snowy day” where no snow has fallen. Important decisions, such as the closure of schools, must be made at night, when winter precipitation should start during the early hours of the morning. If the temperature is a little higher than expected, winter precipitation falls like rain and you have the wrong forecast.
For example, it is essential to know the elevation of the rain-snow line in Colorado to see if any of the mountain passes along Interstate 70 may remain open. In New York, it is crucial to know whether the rain-snow line will reach the I-95 corridor or remain west.
Why are bridges the first to freeze?
During the winter, bridges and viaducts are the first to freeze. This is because they have air on all sides, so they cool faster than surface roads. Surface roads are naturally more isolated because cold air is just above the surface, while the ground below keeps the road warmer.
So you have what is called a winter mix. It’s basically a little bit of everything. When you are close to the rain and snow line, the rain can change to hail over time and then change to snow. Or the snow will transition to rain.
Meteorologists have the important job of not only identifying what type of precipitation will fall, but also timing when one type of winter precipitation will transition to another.
It is crucial to know what time the rain will change to snow. Will this happen before the night shift or after?
It is challenging, no doubt, and not always perfect. But knowing what will fall and when is the key to staying prepared in the winter.
CNN meteorologist Taylor Ward contributed to this report.