If I were to tell you one of our forecasts we just 25 miles off several days out, you probably would consider that a good or very good forecast, right? If you ask folks in the Boston, Philly, and D.C. area, they would agree, this was an excellent forecast with 4 to 5 days of lead time. Boston was prepared for a low-end plowable event, and Philly to D.C. was prepared for potential record-setting snowfall. In between, however, in the NYC area, things were not so clear. In fact, many would argue this was one of the poorest forecasts in history, especially considering this storm ended up being historic: Newark, JFK and LaGuardia airports each had single storm snowfall records broken. But what led to 6 - 12" forecasts turning into 20 - 30" ones? And was this actually a poorly forecasted event? Let's break this down further and discover the difference between 25 miles.
It all started Monday into Tuesday, January 18th and 19th. A storm we had been watching for several days prior was finally looking likely to take aim at the Northeast. And this wasn’t just any storm, it had the potential to be a historic one – one that was a near replica of the Blizzard of '96. Alarms were sounded as the entire I-95 corridor began to prepare. However, many forecasters were careful still being 100+ hours out, and overall social media was a bit quieter than normal – perhaps a lingering effect of the “Blizzard That Wasn’t” last year. But come Wednesday and Thursday, it was time to begin making more specific forecasts at 48 – 72 hours before the event.
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By Wednesday and Thursday, Boston was prepared for a 2 – 4” storm, while Philly, Baltimore, and D.C. all were preparing for at least 1 to 2 feet of snow! In fact, even into Central Jersey, 1 to 2 feet of snow was expected (see image below). However, just north into North Jersey and the NYC metro, forecasts were fluctuating and confidence was lowering as models began to key in on an extremely sharp gradient. With a slight southern trend (see Thurs-Fri model loop above), this gradient was projected to be right through that area, lowering totals from a foot plus on Wednesday, to Thursday and Friday thinking a general 6 – 12” type storm with significant variation from the Hudson Valley into NYC metro and North Jersey. Even within 24 hours from the event, the question remained, “What if the track shifts 50 miles, or even just 25 miles? Would we be prepared?”
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So this raised the question: As a forecaster, what do you do in the NYC area when you know with good certainty 25 miles south will see at least 12 – 24”, and 25 miles north will likely see < 6”? You understand that you can’t possibly nail a forecast to the nearest mile – especially a few days out. And you understand that just a 25 mile swing will be the difference between 4 and 24 inches. I can say for sure, after this year's and last year's blizzards, meteorologists have begun to perfect the art of portraying uncertainty to the public. At WeatherWorks, that is exactly what we did. From 5 days out to 1 day out, we made sure our clients understood this was a lower than normal confidence forecast, and that just a few miles would make a huge difference. So despite forecasts not pin-pointing totals until Friday Night when the snow was beginning, in my opinion this was not a bad forecast at all – in fact, I may argue this was a good one. The fact that we are able to forecast gradients like we did, and the fact that we recognized the potential for the forecast to go wrong, is impressive.
This was an unfortunate situation where there was almost no right answer 1 – 3 days out. The very top image shows the visible satellite following the storm, next to observed snowfall totals. The 2 to 20” gradient over 25 miles was through extreme Northern NJ and the southern Hudson Valley. Basically, the forecast we had was for this gradient to be just to the south, through Northern NJ and NYC. That slight difference was the reason for the drastic swing and why forecasts jumped from 6 – 12” to 20 – 30”. So, I ask again, if I were to tell you our forecasts were off by 25 miles, you probably would say that’s not bad, right? Well, that 25 miles was the difference between 25 inches.
