Not all winter storms bring snow.
While certain types of winter storms can bring large parts of the country to a standstill, it is crucial that forecasters do their best to get the type of winter weather expected right the first time.
Winter precipitation in a nutshell
There are three basic types of winter weather. This includes snow, sleet, and freezing rain. What type of precipitation will fall depends on the air temperature at different levels of the atmosphere.
If the air temperature in the atmosphere is below freezing, snow is expected. If there is mix of warm air in the upper part of the atmosphere, but cold air in the lower part, you can expect sleet. Sleet results when the warm air produces rain. As the rain hits the cold air, it freezes just before hitting the surface. This is what most people hear during winter storms.
If the atmosphere is above freezing until right at the surface, you get freezing rain. This is the most dangerous and can result in black ice on surfaces. Because it freezes to anything on contact, widespread power outages can happen when power lines sag and collapse under the heavy weight.
Why get it right the first time?
While a lot goes into forecasting a winter storm, the hardest part is actually knowing what type of precipitation will result.
Deciding where the rain ends and snow begins is especially important in places where snow is a daily part of winter. Cities and states need to know when to deploy plows, de-icing machines, airport winter maintenance crews, and close schools. This is just the beginning too.
We often hear about the rain-snow line, but what exactly is it? Simply put, it's the point where the rain ends and the snow begins.
If inaccurately forecasted, a city expecting to get only rain could end up with snow. This can be disastrous in places like Houston, Texas. The city is not used to snow and ice accumulation and relies on sanding to keep roads and bridges open.
The same is true if a city is expecting snow and ends up with rain. Taxpayer money will have been wasted on unnecessary plowing and de-icing efforts.
Most people living in the South can recall at least one "snow day" where no snow fell. Key decisions need to happen overnight when wintry weather is expected to happen during morning hours. If the temperature is warmer than expected, you have a busted forecast.
Why bridges and overpasses freeze first
During winter weather, bridges and overpasses freeze first due to having air on all sides. This results in faster cooling than road surfaces.
You also can have what is known as a wintry mix, which encompasses a little of everything.
Forecasters have the important job of knowing what type of precipitation will fall, where it will fall, and when a transition from one type of precipitation to another will occur. While it's challenging and never perfect, modern technology has greatly helped forecast when and where winter storms will hit.
