Winter Storm Stella Wasn't Really a Forecast Bust – Except Along I-95

Jon Erdman
Published: March 14,2017

Winter Storm Stella garnered its share of headlines in the Northeast, but not necessarily the ones some meteorologists expected.
The Daily Mail called Stella "The Blizzard that WASN'T." The New York Post declared "NYC Blizzard is a Dud." The New York Times – in a more muted form on its online front page – declared "New York City is Spared the Worst as Storm Slams Northeast."
(MORE: How Winter Storms Are Named | Winter Storm Central)
Here's how big of a forecast bust Winter Storm Stella really was, and what lessons can be learned for future snowstorms.

What Happened

weather.com interactive radar centered on the New York City Tri-State area at 10 a.m. EDT, March 14, 2017, during Winter Storm Stella.

The track of Stella's surface low was closer to the Northeast seaboard than anticipated, ushering in warmer air to parts of the Interstate 95 corridor from southern New England to the mid-Atlantic states.
This allowed some sleet, freezing rain and even regular rain to encroach into this corridor after an initial round of snow, cutting down some expected snowfall totals along the I-95 corridor.

Was It Really a Bust?

No doubt a forecast bust was the perception along I-95 and closer to the coast with Stella. Given the hype this storm received, it's understood why tens of millions thought Stella was a dud if it didn't shut down the city.
Below was The Weather Company/weather.com's forecast prepared on Monday, one day before Stella began hammering the Northeast.

Winter Storm Stella Northeast forecast made on March 13, 2017, one day before arriving into the Northeast.

Note the forecast snowfall intervals for Boston (Logan International Airport), New York City (Central Park), Philadelphia (Philadelphia International Airport) and Washington D.C. (Reagan National Airport), while a general swath of at least a foot of snow was expected inland from I-95.
Clearly, our forecast snowfall was too high for the I-95 corridor south of New York City. What is not shown above was our snowfall forecasts, which nudged upward above a foot in our forecast issued Sunday afternoon.
For several days prior to Stella's arrival, meteorologists at weather.com, The Weather Channel and the National Weather Service mentioned the substantial uncertainty along the I-95 corridor.
"We knew all along there would be a changeover for the coastal cities," said weather.com meteorologist Ari Sarsalari. "This slight jog left in the track wasn't a huge change to the forecast, (it) just brought the changeover to a mix (sleet/ice) or rain a little earlier than expected – enough to kill the blizzard warning for NYC."
(MORE: The Toughest Places to Forecast)
Despite all that, as of this writing, New York City's Central Park had picked up just over 7 inches of total snow – not too far below our forecast. Furthmore, as The Weather Channel senior meteorologist Stu Ostro pointed out, one location just 4 miles from The Bronx picked up over a foot of snow.
In parts of the I-95 corridor, it wasn't snow or rain, but rather an ice storm early Tuesday that, when coupled with wind, led to tree damage and power outages.
Don't tell anyone in the Northeast's interior that Stella underachieved.
Prolific snowfall rates up to 4.5 inches per hour were observed west and north of I-95, particularly in a corridor from central Pennsylvania and northern New Jersey into central and upstate New York. In some areas, traffic was snarled from 1 to 2 feet of snow.

The video above was taken in Poughkeepsie, New York, on March 14, 2017.Winds gusted over 60 mph along parts of the coast, from the Jersey Shore to Long Island and the southern New England coast, as Stella underwent bombogenesis, a rapid strengthening of the low-pressure center.
Coastal flooding along parts of the Jersey Shore was no less impressive, topping 3 feet above normal tides at Atlantic City, which prompted water rescues.
(MORE: 5 Reasons March Weather Frustrates You)

The video above was from Ocean City, New Jersey, during high tide on March 14, 2017.

Takeaways For Snowstorm Forecasts

Was our snowfall forecast for Boston, New York, Philadelphia and Washington D.C. too high? In some places, yes.
Was Stella a forecast bust overall? Based on all the impacts listed above, we have to say no.
Going forward, here's what you should remember about snowfall forecasts.

Take Exact Snowfall Forecasts Beyond 48 Hours from the Storm With a Grain of Salt

Most National Weather Service offices will not issue a snowfall total forecast – for example, X to Y inches forecast for Anytown – until it's within 48 hours of an event.
This is because, as we saw with Stella, subtle changes in the track of low pressure, interaction of multiple ingredients and the presence of small-scale heavy snowbands can be difficult to forecast, even 1 to 2 days before the storm, by today's most sophisticated numerical forecast models.
At weather.com, we'll often post a snowfall outlook without snowfall totals to give you a general idea of where the heaviest snow may fall. Below is an example from the weekend before Stella hit the Northeast.

Winter Storm Stella Northeast snowfall outlook made on March 11, 2017, three days before arriving into the Northeast.

What we typically tell you several days away from a potential storm is:

1. There is a possibility of a storm.
2. The storm may occur during a given time frame.
3. Details like snow/ice totals for specific cities are to be determined.

Monitor for Forecast Updates

This is the most important point. You need to check back frequently for updates.
A forecast issued two days before the storm isn't gospel. As the storm gets closer, the forecast frequently changes.
For example, here is an animation showing 16 consecutive model forecasts for Tuesday at 2 p.m. EDT, produced from four days prior to the snowstorm until the morning of the snowstorm, courtesy of Levi Cowan at tropicaltidbits.com. The snowy areas are shown in blue, while rainy areas are shown in green, yellow and orange.

16 consecutive GFS model forecasts for 2 p.m. EDT, March 14, 2017, of Winter Storm Stella in the Northeast. Areas of snow are shown in blue. Areas of rain shown in green, yellow and orange. The model forecasts were generated from March 10 (first frame of animation) through March 14 (last frame).

Notice all the precipitation areas jostling around near the Northeast coast, from a soaking rain to heavy snow? That's a common problem in a model forecast several days in advance.
In practice, meteorologists incorporate data from not just one forecast model, but a consensus from multiple models – including clusters of models called ensembles – to adjust their forecasts.
These groups of model solutions often change, sometimes radically, from day to day.

Small Forecast Changes = Big Impacts

If the forecast for your area changes significantly, as we mentioned earlier, it may be a subtle, 50-mile-or-less shift in the track of low pressure that makes all the difference.
Consider Stella on Tuesday morning; just a small distance separated rain in western Long Island from over a foot of snow and whiteout conditions in the northern New Jersey suburbs.

Read the Fine Print

Long disclaimers when installing a new app can make eyes glaze over, but forecasters will spell out important details in their videos or columns you may not get in a graphic alone.
For example, weather.com meteorologist Chris Dolce made an important point atop a Monday morning Stella forecast article.

In short, you may read or hear about trends in the forecast, which may have an impact on the ultimate outcome in your location.
Similar to digging deep into a news story rather than just reading a headline, listening to the forecaster gives the full picture, not only on what the forecast is right now, but also the uncertainty in the forecast and how it may change.
Virtually all snowstorm forecasts have challenges and will continue to test the minds of meteorologists. It's truly a humbling line of work and, personally, I've busted more forecasts than I care to admit.
However, based on the evidence, Stella wasn't nearly as big of a forecast whiff as you may hear.

MORE: Winter Storm Stella

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