‘Tis the season to be … wary! Yes, it’s that time of the year again, when Twitter and Facebook feeds light up with all sorts of colorful weather maps filled with big numbers and terrifying words that warn us all of impending meteorological doom.
Major snowstorm on the way! ... Blockbuster winter storm looming! ... Blizzard to blast eastern United States!
This happens every year, just as the leaves always turn colors and drop to the ground. And same as snowflakes eventually fall from our skies when the weather turns cold and moisture fills the air.
But don’t trust everything you read — especially on social media. Especially weather alerts that are posted by amateur weather enthusiasts who are not trained meteorologists. And especially predictions that are posted many days before a storm system even develops.
Many of those posts — like the ones you likely have been seeing, and perhaps sharing, during the past few days because of two potential winter storms looming next week — are based on one run of computer guidance models. Those are the special computers that spit out all sorts of weather projections about every six hours, based on current data that is fed into them.
Professional forecasters often remind the general public that computer models, even the major ones like the European model and the American GFS model (formally called the Global Forecast System) are not official forecasts. They are among the many tools used by meteorologists to analyze storm systems, weather patterns, wind direction, air temperature and other atmospheric conditions.
Computer models typically become more reliable one to three days prior to a storm. When a storm is more than several days away, models can be way off on their projections. Sometimes those early projections turn out to be spot on, but sometimes they tank.
So, if you happen to be seeing Twitter posts with computer model maps showing projections of 12 to 18 inches of snow for New Jersey and other eastern states this upcoming Wednesday into Thursday, keep in mind, that’s usually one particular model output from one particular guidance model. (There are literally dozens of computer models used by forecasters all around the world.)
Weather professionals say the general public should be skeptical over social media posts that show extreme snowfall totals or make predictions many days before a storm arrives.
“Stay with who you trust,” said Robert Deal, a meteorologist for the National Weather Service’s regional forecast office in Mount Holly, which issues forecasts for most of New Jersey, all of Delaware, most of Maryland and eastern Pennsylvania.
“That’s what we recommend,” he added. “Get the information from trusted sources,” like the National Weather Service and local television meteorologists.
“People are going to share stuff on social media, and we can understand that,” Deal added. “Any time people can find snowfall maps that suggest there could be more than a foot of snow in the Northeast corridor, you’re gonna get people talking and asking questions.”
The problem is, not everyone who is posting weather forecasts on Facebook and Twitter are actual meteorologists or trained on how to interpret complicated data coming from computer guidance models.
“Many of the maps that you currently can see artificially choose a liquid-to-snow ratio of 10 to 1,” Deal said.
With a 10-to-1 ratio, 1 inch of liquid in the atmosphere will produce about 10 inches of snow. And 2 inches of liquid will equate to about 20 inches of snow.
However, Deal noted, “that’s not always the standard.” That’s because every snowstorm is different, with varying temperatures in different layers of the atmosphere, dry air pushing in to limit the amount of moisture, and other factors, like wind direction and the speed of a storm.
Sometimes a storm is expected to move very slowly, generating higher rainfall or snowfall totals. But sometimes a storm will pick up speed and move out more quickly than initially expected, cutting down on the final totals.
What to expect next week
So, what should New Jerseyans expect for Wednesday’s storm?
Deal says the National Weather Service has growing confidence that a large coastal storm will develop and there could be “significant snowfall for portions of the forecast area.”
The big questions, however, are where, and how much snow?
For now, the weather service is not issuing specific snowfall projections in its forecast, because the storm is still more than four days away and a lot of factors can change, Deal said. For example, the exact track of the storm and the air temperatures will play a big role in how much snow falls in New Jersey and which areas may get a mix of rain and snow, or plain rain.
Could New Jersey really get slammed with 12 to 18 inches of snow next week, as some social media posts are claiming?
At this time, Deal said snow totals over a foot cannot be ruled out. But, once again, it all depends on multiple factors, like the storm path, its strength, how cold the air is at different layers of the atmosphere and — as mentioned earlier — the ratio of liquid to snow.
The bottom line: In another day or two, the National Weather Service and other professional forecasters will have a better handle on how Wednesday’s storm will play out. And they will start issuing their own forecast maps.
Maybe those maps will turn out to be as scary as some of the ones making their rounds on social media. Maybe they won’t. But at least you’ll know they came from trained meteorologists who specialize in interpreting complicated data.
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Len Melisurgo may be reached at LMelisurgo@njadvancemedia.com. Tell us your coronavirus story or send a tip here.
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Listen up, New Jersey: Don’t trust all those wild snowfall predictions flooding social media - NJ.com
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