At a Glance

Forecasts for winter storms can be uncertain even a day or two in advance.Maps showing long-range snow forecasts from individual computer models are not reliable.These maps can change dramatically in a short amount of time.

Major winter storms affect theUnited States every year, and due to their significant impact on everyone's lives, the biggest question asked is, "How much snow am I going to see?"

The eagerness to know how muchimpact a snow or ice storm will haveis understandable, but unfortunately, sometimesthat question cannot be answered until within one to three days of its arrival.

Thisthirst to know what will happen can often be fed by those computer model forecasts of snow amounts that often go viral on social media. Sometimes you might see these maps with vibrant blue, pink and purple shadings up to a week or so in advance of a storm's arrival.

Example of a snow model forecast with different colors representing snowfall amounts.

While these maps will never disappear from social media in the winter season, and there is nothing that can be done about it, you can do your part by not buying into what they are showing and also not sharing them.

Check out these examples for more proof of why you should not fully trust long-range model snowfall forecasts.

Forecasts Can Change Dramatically in 12 Hours

The animation below shows two separate forecasts from the same computer model about 5 days in advance of a potential winter weather event in the South. These two forecasts were generated by that model just 12 hours apart, yet they have drastically different outcomes.

Model Forecast No. 1 indicates a solid area of snow or a mix of wintry precipitation just to the north of the Gulf Coast, from Texas to Mississippi. The second version, labeled Model Forecast No. 2, has almost no precipitation in the exact same areas since the area of low pressure tracks too far south in the Gulf.

This is an example and not a current forecast.

Another way to look at this is by seeing how forecasts for snowfall amounts several days in advance of a potential storm can change dramatically in a short amount of time.

The animation below shows three separate snowfall forecasts generated 12 hours apart from the same computer model in Texas and Louisiana.

Sure, there is a consistent signal for some accumulating snow in these areas (grey and blue shadings), but notice how the geographic locations and snow amounts from each model run – labeled 1, 2 and 3 – change drastically. The snow forecast totals go from 2 inches or more in parts of Louisiana and eastern Texas in Model Run No. 1 to little or no accumulation in those same areas in Model Run No. 3.

This is an example and not a current forecast.

Thistype of flip-flopping is commonly seen in long-range snowfall forecasts, further proving that the snow maps you may see on social media are anunreliable source of information.

On top of that, those maps often don't take into account how much snow can be produced from the forecast amount of liquid-equivalent precipitation, also known as the . Snow totals on the maps can also be inflated in areas where sleet is expected rather than snow.

​​​Why Do the Forecasts Change?

Many times, the potential for a significantwinter storm is apparent to meteorologists five to seven days in advance. This is diagnosed using some of the same forecast models that generate those viral social media snow maps.

Forexample, on a Monday morning, there may be indications in forecast model guidance that a winter stormcould affect several regions of the U.S. the following Friday through Sunday. Instead of specific details, meteorologists usually notify the public that we are watching for a particular storm in a general time frame. This is typically followed by the caveat thatthe forecastwill change and we will provide more details as they become available.

Part of the reason to expect forecast changes over time is that weather disturbances triggering thedevelopment of a potential winter storm might be thousands of miles from their future destination. That means they may be traveling over a data-void region such as the Pacific Ocean before they reach the U.S.

As a result, forecast models may have difficulty resolving important details of how a winter storm may come together from thatincipient disturbance(s). It's a basic concept of forecast models that have initial errors in analysis or short-term forecasts amplify with time.

Throw in questions surrounding the location and depth of the cold air source, and there are countless scenarios forecasters are faced with when there's a winter storm in the long-range forecast.

So the next time there is potential for a significant winter storm in your area, resist the temptation to run with the forecaston any snow map(s) you might encounter on social media.

Instead, consider the source. If the person who posted the image isn't a familiar face that you've seen on TV, a trained meteorologist from the National Weather Service or private forecast company such as The Weather Channel, a quick Google search of their name will almost always tell you in less than 30 seconds if this is a reputable source. Trained meteorologists should not be sharing a wild forecast for a week into the future, and if you can't find the person's portfolio and credentials in a web search, that's a red flag.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, .