If you’re an avid weather enthusiast, than you’ve probably already seen discussions of a potential major snowstorm right before New Years. Even those who don’t track storms as rigorously have probably already heard rumors of possible heavy snow to close out the year. Guidance has been quite consistent on showing big storm potential between the 29th and 30th of December, and per usual, the models aren’t sold on one single outcome just yet. With the storm being a full week away, this shouldn’t be a surprise to anyone.

We can’t argue with the fact that the potential for a major east coast snowstorm is certainly there, but the question remains will all pieces of the puzzle come together in time to bring a big storm into fruition? We’ll show you the latest analysis on what’s going on, and hopefully will be able to clear some questions up along the way.

Over the last 48 hours, all the computer model guidance that we use as tools to help forecast the weather, have shown a major snowstorm impacting the east coast at one time or another. The latest guidance doesn’t seem to show the same confidence as it once was on an all-out blizzard scenario, but that doesn’t mean it won’t necessarily go down that way.

There are many players on the field with a storm like this, including several different jet streams, and four different areas of energy. How all of these component interact will ultimately determine whether or not we get a major snowstorm in the air.

If we look at the US Model, the notorious GFS, we see the changes the model has gone through over the last few days in regards to both the upper-level 500 mb pattern as well as the surface result. Just yesterday during the evening hours, the GFS was predicting a possible blizzard impacting I-95 and back inland towards interior New England. This morning? Not much. The major difference we saw between these model runs separated by less than a day, is the difference amongst how fast our pieces of energy phase together.

The image above shows this morning’s run of the GFS (6z), valid for this upcoming Friday. What you can see is all the players on the field. We have 2-3 distinct pieces of energy associated with different upper-level jet streams, as well as two key features: a ridge out west, and a trough in the center of the country.

Moving forward into Saturday, you can see the ridge out West beginning to flatten, as our trough moves quickly to the East. This allows our two northern pieces of energy to begin interacting and phasing together. Remember, when we get these different jet streams to phase their energy together, we increase the chance of a more potent storm. At this juncture, according to the 6z run of the GFS, the trough doesn’t dig as much with a flatter ridge, and heights don’t rise as much along the east coast. This makes a full phase of all the energy more difficult. In turn, this makes a big snowstorm more difficult, should this run of the GFS be correct.

As we move into Saturday morning and midday, you can see our ridge out west nearly collapses completely. This is likely in-part due to a new piece of energy coming out of the Pacific Northwest pushing down on the ridge and allowing it to flatten out. With a flatter ridge, our trough doesn’t dig as much, and energy from even further south misses the phase completely or phases very late in the game. This results in a storm that doesn’t produce big totals. In this type of scenario, we’d either see a brush of heavy snow to the Mid-Atlantic, or a storm that doesn’t come together until its well offshore.

Looking at the surface result from the 6z GFS, you can see that exactly. The storm quickly scoots off to the east, and follows much of the energy that remains offshore. Instead of a big snowstorm, we get some light snow showers with the heaviest stuff remaining over the ocean.

However, there’s reason to believe this is incorrect. Just a few runs early, and subtle changes in the upper-atmosphere at 500 mb showed a much different result at the surface.

Here’s the run of the GFS from yesterday afternoon (18z). You can see this is for the same time period next Friday, and already there are some notable differences from this mornings 6z run. The ridging is a bit more potent and further to the west, which allows the trough to dig a little more and also become more expansive. With everything further west and deeper, heights can rise ahead of the system, making a negative tilt in our trough more likely. This overall setup is more conducive for a big snowstorm.

Moving forward, you can see our ridge starting to breakdown again, but it’s situated further west and allows our trough to become really expansive and cover a very large area. It’s also very deep, allowing for more energy interaction between all pieces of energy. The heights ahead of the storm are still fairly high, so we get more tilting of the trough. The energy is then forced together.

Notice that by Saturday afternoon, our ridge holds itself (as opposed to this morning run which showed it breaking down completely), our trough doesn’t jet off to the east, and we still see a fair amount of digging. There’s nearly a full phase of energy over the region. THIS is what will bring you a major snowstorm around the 29th or 30th of December.

Notice how dramatic the changes are down at the surface. With all the energy bundled together, our low pressure is concentrated just east of Boston, and is down to nearly 980 mb (very strong). Heavy snow and strong winds are spreading from New York City to Boston to Bangor. If energy had phased a few hours earlier, the entire I-95 corridor from Washington DC to Caribou Maine would see a similar result.

So what do we believe then? Are the prior runs to the GFS correct and we get a classic east coast snowstorm, or is the newer data catching onto something and the storm won’t end up producing much? The truth is, it’s too soon to tell. Being a week out, models are going to continue going back and forth with these different types of solution until energy is fully sampled. And then won’t happen for another few days.

For now though, we can still get a good idea of what’s going to happen based off history and the overall setup we’re seeing. The GFS has a progressive bias, meaning it likes to rush things. It’s very possible that some of the more recent runs of the GFS are tapping into that bias, making less potent features and less phasing. The most recent run of the ECMWF (12z) is beginning to show less progressiveness, and hinting that indeed the GFS might be underestimating some things. The big takeaway for today should be that there is enough potential here to begin discussing the POSSIBILITY of a major snowstorm between the 29th and 30th of December. We’ll have a decent setup in terms of a ridge out west and a trough in the east, and energy will be close enough together that only slight changes could make the difference between a major storm and almost nothing at all. What we really need to see is the ridging in the west hold more, and the trough in the east become less progressive, more expansive, and tilt negatively. If this happens it will draw all our energy together. Should that happen, we will have a very large snowstorm on our hands this time next week.

The above scenario is our “best guess” at what may result from all of this just before New Years. With that said, we caution folks to take this depiction lightly, as changes and wobbles in the forecast are expected. Should things come together just in time though, something like the scenario above is a likely solution. If things come together on the earlier side, you can expect the solution above to be expanded, possibly reaching further south and further inland as well. A solution where the energy doesn’t come together in time, and most of this shifts offshore, is also a slight possibility.

There’s a lot to watch over the course of the next week, and we’ll be constantly updating you with the latest on what is to be expected. In the meantime, know that there is potential for a snowstorm of some kind just before the new year begins.


Scott is the founder and CEO of WeatherOptics Inc, which he started as a weather forecasting content platform in 2010. In 2016, after gaining a substantial following, WeatherOptics began servicing the private sector using impact analytics driven by historical weather data. Since this pivot, Pecoriello has led the effort to combine consumer, business, utility, and weather data in order to redefine how WeatherOptics could change business perspective on the weather. As founder as well as the director of all day to day operations, Pecoriello has proven WeatherOptics to be an effective, fast-growing data analytics company that is actively changing the way businesses think and react to the weather.

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