The Science Behind X-Factors for Thursday’s Nor’easter

You know the nitty gritty for Thursday’s storm, and for most that’s all that is required. Wicked snowy, school is cancelled, stay off the roads if you can, politicians will hold a bunch of press conferences about how many plows are out, and goofy meteorologists such as myself will be standing outside. Great! But if you’re interested in a few of the technical details and other things to watch, here’s a deeper dive into the geek files.

BANDING

Most nor’eastahs have a broad swath of snow, but they also produce localized banding. These are areas where there’s strong convergence in the atmosphere, which means air is coming together along a point. When this happens, air has nowhere to go but up! Rapidly rising air = lots of condensation and in turn a load of snowflakes. So these bands are important when it comes to jackpot zones.

fronto The Science Behind X Factors for Thursdays Noreaster omega The Science Behind X Factors for Thursdays Noreaster

For Thursday, there are signs that there will be some very intense lift. We can see that using guidance like this. ‘Omega’ is vertical velocity – essentially gauging rapidly rising zones of air. It points to extreme snowfall rates of 2-4″/hr tracking out of Connecticut and into Rhode Island – Massachusetts for the late morning to mid afternoon hours. These bands are somewhat unpredictable. With rates like that, you could see a few towns stack up 18-24″ of snow Thursday. It’s tough to include that in an official forecast because it’s not easily pinned down. But it’s important to know the potential is there.

THUNDERSNOW!

You bet your sweet Jim Cantore there will be thundersnow in southern New England Thursday. This goes along with the section above as it pertains to rapidly rising air. That extreme instability will almost assuredly produce thunder and lightning tomorrow in those strong bands. Locally, odds favor about 11am-4pm for that to occur. Get your time lapse camera set up and enjoy.

 

A QUICK MOVER 

The only thing keeping this storm from being an absolute blockbuster is its speed. If there was stronger blocking over the North Atlantic, we could cage this puppy in and maximize those high snowfall rates…and we’d be talking 2-3 feet of snow. But it’s embedded in a progressive flow. So even though it will rip snow for several hours tomorrow, the most intense part of it will not last long enough to hit those hall of fame amounts.

tides The Science Behind X Factors for Thursdays Noreaster

This is also important because it keeps coastal flooding from being a larger issue. It’s forming quickly, and leaving quickly. So fast, in fact, that winds will be onshore for the morning high tide but already turning northwesterly by the evening. Pockets of minor coastal flooding are likely during the morning cycle, but by the 9-10pm high tide most of the Seacoast to South Shore will have offshore winds. The Bay Side of the Cape may see another round of minor flooding. I’d wager overall, the coastal situation won’t be quite as bad as the storm we had in early January.

ALL SNOW? POSSIBLY NOT

While the vast majority of the storm will be snow across the entire region, it may still be mild enough across SE Mass (particularly Cape Cod and the Islands) to start off as rain. That will not last for long though, so don’t freak out if you see raindrops first! And what will start as a wet snowfall in those milder locales will turn fluffier as the storm goes on. Temperatures will drop off into the 20s during the afternoon across the Cape and Islands, so the sticky consistency will start to become a snow more prone to blowing and drifting.

It’s because of this chance of initial rain, plus some sticky snow to begin with, that I kept the totals a little lower for the Lower/Outer Cape and Nantucket. We may make up for lost time with banding during the 2nd half of the storm, but it’s a tough call. Either way, plenty of snow and poor visibility for mid-morning onward.

HOW COME THIS BECAME SO BIG, SO FAST?

On Saturday, it looked like we might be in the clear. By Sunday, snow was back in play. By Monday, it was game on. And by Tuesday we were talking about possible blizzard conditions. So what changed? In winter, it’s all about timing. Disturbances in the atmosphere have to meet up at the proper moment to reach maximum potential. If they’re out of phase, in the wrong places, or lack the right air masses, you don’t get the storm. Early in the weekend it looked like this energy would slide out to sea before it could get grabbed by an arctic-origin disturbance and phase. But as it turns out, the southern-stream storm out ahead of the duo (the same that produced tornadoes in Louisiana Monday) helped set the table.

http://www.ssd.noaa.gov/goes/east/eaus/wv-animated.gif

That lead disturbance ramped up and helped slow down the one behind it just enough for the arctic energy to meet it. Now, as the dance comes to its final movement, the merger will give us a rapidly deepening storm closer to the shoreline, and voila – snow! It can be both frustrating and fascinating to watch these interactions take place.

WHEN’S THE LAST TIME WE HAD A STORM LIKE THIS?

Well, we did have 12-20″ of snow just a month ago across southeastern Massachusetts. But it was on a Saturday, it melted in 3 days, and no one really seemed to notice. And in the city of Boston it produced a little over 8″ of snow.

Considering the forecast tomorrow and our weak sauce winter last year, this one should be the largest in Boston since the epic 2015 run a couple years ago. I don’t think we’ll hit that 2 foot mark, but we should certainly top a foot and that my friends is a legit New England snowstorm. Fortunately winds shouldn’t be damaging in a widespread sense, and coastal flooding won’t be a huge problem with this one either. Just a big blast of snow and then it will be on its way.

snowstorms The Science Behind X Factors for Thursdays Noreaster

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