Snow forecast maps on social media: What to know

Major winter storms affect the United States every year and bring with them major disruptions to daily life.

In order to understand how big a disturbance one might cause, the most pressing question is always: How much snow will I see?

(More: Winter storms 101)

Patience is required when it comes to snowfall forecasts: Wanting to know the extent of the impact of a snow or ice storm is understandable, but unfortunately, sometimes that question can only be answered within one to three days of its arrival.

This thirst to know what will happen is often fueled by computer model projections of snow amounts that often spread on social media. Sometimes you may see these maps with beautiful blue, pink, and purple lines up to a week or so before a storm arrives.

There is nothing that can be done about these maps; They will never disappear from social media. But you can do your part by not buying what they offer and also not spreading it like a bad virus.

Meteorologists may see signs of a major winter storm five to seven days in advance, but it’s too early to make a specific snow forecast: For example, there may be indications in the forecast model guidance on Monday morning that a winter storm could affect several areas of the United States the following weekend.

Instead of offering specific details, forecasters usually give a heads-up that we’re watching a particular storm in a general time frame. This is usually followed by a warning that the forecast will change and we will provide more details as they become available.

Without robust data, numerical forecast models may have difficulty resolving important details about how a winter storm builds up from those initial disturbance(s). It is a basic concept of forecasting models that initial errors in short-term analysis or forecasts grow over time.

If you ask questions about the location and depth of the cold air source, you’ll find a myriad of uncertain scenarios that forecasters face when dealing with a winter storm in a long-range forecast.

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These uncertainties lead to the volatility often seen in long-term snowfall forecasts from computer models: For example, you might see a map posted on social media showing 8 to 12 inches of snowfall (running model #1 below) for your city from a storm that is still five or more days away. This same model can change its tune and predict 3 to 5 inches at the next update 12 hours later (model run #2 below).

Furthermore, these maps often do not take into account the amount of snow that could be produced from the expected amount of liquid equivalent precipitation, also known as the snow fraction. Snow totals on maps can also be inflated in areas where rain is forecast instead of snow.

Here’s what to do next time you hear about the potential for a major winter storm in your area: First, resist the temptation to follow the forecast on any snow map you might encounter on social media.

Instead, consider the source. If the person who posted the photo isn’t a familiar face you’ve seen on TV, a trained meteorologist from the National Weather Service or a private weather forecasting company like Weather.com, a quick Google search of their name should almost suffice. I always tell you in less than 30 seconds if this is a reputable source.

Chris Dolce He has been a senior meteorologist at Weather.com for over 10 years after starting his career with The Weather Channel in the early 2000s.

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