Blizzard conditions along a highway. South Dakota Highway Patrol photo, 2020.
National Weather Service meteorologists from the Northern Indiana office and elsewhere have used the “B word” when writing about the winter storm that’s forecast for Indiana later this week.
For example, a winter storm watch that the Northern Indiana office issued today includes the phrase, “blizzard conditions possible.”
When I was a kid, depictions of blizzards in movies and TV dramas led me to think of a blizzard as a very bad, very dangerous storm that drops huge amounts of snow.
It wasn’t until much later that I learned that the meteorological definition of “blizzard” has nothing to do with accumulation!
What really defines a blizzard is how strong the wind is and how far you can see through the snow and blowing snow. The National Weather Service website defines “blizzard” as “blowing and/or falling snow with winds of at least 35 mph, reducing visibilities to a quarter of a mile or less for at least three hours.”
This means that if the wind is strong enough and the forward visibility is low enough, you can have blizzard conditions without large accumulations!
Travel in northern Indiana could be extremely dangerous Friday, no matter how much snow falls, because strong wind could cause white-out conditions. Making the situation even more dangerous will be extreme cold, which would be especially bad for anyone who slides off a road and gets stranded in a ditch.
It’s wise, therefore, not to focus too much on accumulation forecasts with this storm. The wind, visibility and cold could be dangerous even in areas where accumulation is relatively light.
The biggest reason is that meteorological science isn’t capable yet of forecasting the exact track of a low pressure system four days in advance.
I’m not a meteorologist, but I’ve spent enough time collaborating with meteorologists to develop a fair understanding of their work. So, I’ll try to explain here what I know about the coming storm, based on what the pros have published.
First, it helps to know how low pressure systems affect winter weather. Typically, the heaviest snow falls to the north and northwest of a low pressure system. Areas to the east and northeast usually get mostly rain. Areas to the southeast can get clear skies with little or no precipitation.
The path a low pressure system takes therefore has a major impact on where the biggest winter storm impacts will occur.
The main way meteorologists predict a system’s path is by monitoring the output of special computer programs known as numerical weather prediction models. These programs run on supercomputers, because they ingest massive amounts of weather observation data and apply complex equations in their attempts to create reliable, mathematical simulations of the atmosphere. Several such programs exist, all written differently. It’s not unusual for the various models to produce different solutions, which typically come out every 12 hours.
Meteorologist Megan Dodson at the Northern Indiana NWS office wrote in an Area Forecast Discussion this morning that they’re watching the outputs of at least four different models. They’re paying attention to how much consensus exists between the solutions of the various models and how consistent each model’s output is with previous output from the same model.
As of this morning’s forecast discussion, these models indicated that the low pressure system would move from the southwest to the northeast and that the path it follows would be farther west than previous model runs indicated. The image below, published by the Indianapolis NWS office, shows three possible paths for the system. One model, known as the Global Forecast System (GFS), is an outlier, forecasting the most westward path. If it’s right, and the center of the low stays west of Indiana, the Hoosier state won’t get much snow. Other models forecast more easterly paths.
Graphic published by NWS Indianaolis showing possible tracks of a low pressure system associated with a forecast winter storm
All the models could still be wrong!
Numerical weather prediction is not perfect, but the closer the low pressure system gets to Indiana, the more the models will align and the better the forecasts will get.
As I write this, the system is still over the Pacific Ocean, so it should be understandable that it’s too early for the models to accurately predict how it will track over the Midwest.
For now, it’s important to understand that a winter storm will very likely occur somewhere, but as much as you’d like to know exactly where the most snow will fall (and where the most travel impacts will be), it’s just too early to know.
That said, because it’s also too early to rule out big impacts in any part of northern Indiana, it’s wise to prepare for such impacts. For example, you might shop for Christmas dinner ingredients a day earlier than you originally planned, just in case.
It’s also important to realize that some people who are not meteorologists post official-looking but unscientific forecasts on social media. Often, they choose the single model output that looks the most dramatic (even though it’s an outlier), rather than create legitimate forecasts based on a full understanding of model limitations and model consensus. Often, the main goal of such posts is to create bigger audiences for advertisements. Keep that in mind the next time you see a dramatic snow forecast for any time that’s more than a few days away.
The Northern Indiana office of the National Weather Service (IWX) conducted a webinar for its partners at 3:30 p.m. ET Monday, January 31, to discuss a winter storm forecasted to hit its area in the following days. Here is a summary of the information shared during the initial briefing and subsequent question-and-answer session.
IWX meteorologist expected to upgrade the existing winter storm watch to a winter storm warning for at least part of the IWX forecast area by 3:30 p.m. ET Jan. 31. Update: IWX issued a winter storm warning for some of its counties at 3:21 p.m. ET. Visit the IWX web page for details.
IWX plans to issue a new multimedia briefing via YouTube Wednesday morning and conduct a second partner webinar Wednesday afternoon.
Forecast timeline of expected winter storm weather
Forecasters expect the event to begin with a light wintery mix in South Bend Tuesday evening, with rain elsewhere, eventually changing to heavy snow in all areas, as indicated by the timeline graphic above.
Forecaster confidence on winter storm timing is high. Uncertainty is in the transition from rain/sleet/freezing rain to heavy snow, especially along and south of U.S. 24.
Snow accumulation forecast for first round of snow Tuesday night through Wednesday.
IWX shared the graphic above regarding snowfall total for the first of two rounds of snowfall and cautioned partners that the forecast accumulation numbers are very likely to change between now and the beginning of the storm.
Probabilities of exceeding snowfall thresholds.
IWX shared the graphic above regarding probabilities of heavy snowfall and commented that the storm could be on the order of a one-in-five-year or one-in-ten-year event.
Winds are not forecasted to be significant during this first round of snow Tuesday night and Wednesday. That snow will be fairliy wet and heavy and therefore unlikely to blow and drift.
High winds, blowing and drifting snow are likely Wednesday night through Thursday.
IWX forecasts a lighter, drier snow Wednesday night through Thursday. Combined with wind gusts forecasted to reach as high as 35 mph, significant blowing and drifing of snow is forecast, especially on east-west roads in rural and open areas. Whiteout conditions are possible. Roads could drift back over shortly after snow plows pass through on Thursday.
Wind chills are forecasted to be below zero by Thursday night, causing a potential hazard for any motorists stranded in snow.
IWX forecasts ice accumulation to be brief in most areas, and not a great impact. Ice amounts will be less significant than heavy snow.
Widely shared snowfall forecast map from the European numerical weather prediction model run on Dec. 16, 2013 for the forecast period Dec. 22-23. What actually happened Dec. 22 and 23 wasn’t even close to this!
Winter weather is just around the corner in Indiana, which means so are authentic-looking but bogus long-range snowstorm forecasts on social media.
It won’t be long before we see claims that a storm a week or more away will bring huge snow accumulations. Many will have official-looking forecast maps, like the one above (which turned out to be wrong, by the way).
But these posts won’t be the work of professional meteorologists. Many will be the creations of school kids, passing themselves off as weather experts.
This is Winter Weather Preparedness Week in Indiana, so it seems like a good time to prepare readers for the ominous-looking but unreliable snow forecasts they’ll soon see.
To understand what amateur weather enthusiasts put on social media, it helps to know something about the computer programs that professional meteorologists use to guide their forecasts. These programs are called numerical weather prediction models. They simulate Earth’s atmosphere by describing it in a complex series of very complicated mathematical formulas.
The programs built on these formulas run several times a day on supercomputers around the world. Much of the output of these programs is available on the Web, in both numeric and graphical form.
The output of computerized atmosphere models is inherently inaccurate for several reasons, including:
It’s not yet possible to completely describe our chaotic atmosphere in mathematical equations and
The programs don’t have access to enough data about what our atmosphere is doing at the time they run (e.g. what the temperature, wind speed and wind direction are 10,000 feet over any given part of the planet).
Nonetheless, these programs kick out predictions of what the weather might be at any location at any time, as far in the future as 16 days, despite that fact that no computer or human can reliably forecast the weather that far in advance.
Now, imagine a young weather enthusiast who craves attention and loves snowstorms (because they get him out of school). When he sees an indication of heavy accumulations in the output of a single computer model, he might paste that model’s map into a Facebook post in which he writes a dire forecast of impending doom. Such an amateur forecaster might not be aware of (or care about) the model limitations described above. But she’ll love all the “likes” and shares her post receives!
So how do I know what to believe? First, I’m automatically suspicious of any social media post that forecasts specific snowfall amounts more than a couple days in advance. Second, I ignore any forecast that doesn’t come directly from professional sources I trust, such as:
I set up some Twitter search strings in Hootsuite to help me watch what’s going on with this weekend’s winter storm. Here are links to the same searches on the Twitter website, which anyone can monitor, even those who don’t have Twitter account:
Do not be alarmed. Despite what you might have read on Facebook or Twitter, no big winter storm is forecast to strike the Midwest or Northeast this weekend.
As WANE-TV meteorologist Greg Shoup writes in a his blog, “There are no significant weather patterns this weekend across the entire eastern United States.”
Apparently some attention-starved social network users are forwarding information about a winter storm that happened March 12 of 2014, but without the critical information that it was last year!
Greg correctly points out in his blog that we should not believe everything we read on social media sites. Even when weather information on Facebook and Twitter is current (versus a year old), much of it comes from amateur meteorologists who share worst-case scenarios based on the outputs of single numerical models of the atmosphere, hoping they can claim to be the first to advise the world of some major weather event.
I prefer to get my weather information directly from the National Weather Service (NWS). The NWS is completely taxpayer-funded. Unlike other sources of weather forecasts, the NWS does not crave attention, nor rely on advertising (which relies on viewership) to stay in business. In my experience, if the official NWS forecast does not mention a big weather event, it’s because there’s a good reason that NWS meteorologists lack confidence that the event will occur.
You’ll never see me write my own forecasts here on this blog, on Facebook or on Twitter, because I’m not a meteorologist. I share information from true professional meteorologists who I trust, mostly NWS employees and occasionally very credible broadcast meteorologists, like Shoup and his colleagues at WANE.
So, don’t believe everything you see on social networks and please, don’t share weather information with others unless you know and trust the source.
