For weeks, weather experts have been expecting that early March would live up to its reputation of coming in “like a lion,” with a pattern conducive to major East Coast storms. That expectation is going to become a reality, first during the next three days, and then again next week.
However, the specifics of the weather forecast, particularly what form of precipitation will fall in areas like New York City, Hartford, and Boston, are turning meteorologists’ hair white, and causing weather Twitter to resemble a therapy session.
Here’s what you need to know.
First of all, there’s the broader context. The overall weather pattern is extremely favorable for a monster storm to form and meander close to the East Coast for days. This is because there’s a massive block in the upper level winds, known as the jet stream, blowing across the Atlantic. A huge area of high pressure is sitting over Greenland, rerouting the jet stream to the north, and then back south to the west of Europe, where frigid air from Siberia has been making international headlines.
Because of this block, any weather system that forms near the Mid-Atlantic or Northeast is going to be effectively stuck in place for a while, pinwheeling around, flinging high winds, heavy precipitation, and high waves at the coast.
This block is partly reflected in a see-saw pattern of atmospheric pressure over the North Atlantic that meteorologists keep track of, known as North Atlantic Oscillation, or NAO. When the NAO is in a negative phase, it is more favorable for snowstorms in the eastern U.S. and Europe. Lately, the NAO index has plunged to a record low, which is indicative of how primed the atmosphere is for a major storm.
Second, all computer models are converging on a solution in which a storm will form off the coast of New Jersey late Thursday, and rapidly intensify as it slowly moves to a position near or just south of Martha’s Vineyard on Friday.
On the northern flank of the low pressure area, there will be a powerful easterly flow of air, known as a low level jet, that will transport copious amounts of moisture into southern New England. It will also build up high seas that will batter vulnerable coastal areas, particularly from southeastern New Hampshire to the eastern tip of Long Island.
In Boston, the city recorded its highest-ever water level when the ‘Bomb Cyclone’ struck. The upcoming storm may exceed that, based on current projections.
By far, our greatest concern with Fri-Sat storm is for widespread Moderate to Major coastal flooding along E MA coast over 3 tide cycles! Areas that normally stay dry may flood around high tide. Road closures, basement flooding, & structural damage possible! Prepare now! pic.twitter.com/ibiukszkgQ
— NWS Boston (@NWSBoston) February 28, 2018
Due to long-term sea level rise, storms like this one have a higher likelihood of producing major coastal flooding, because the storm surge and high waves are coming on top of a higher baseline. It’s similar to a basketball court with a slowly rising floor, which would enable players to sink more slam dunks over time.
Moderate to major coastal flooding is expected from Friday through Saturday during high tides from New Jersey to the eastern Massachusetts coast. The flooding is expected to be particularly severe because it’s coming on the heels of a full moon, when tide levels are higher.
Third, there’s the problem of precipitation type. All the ingredients are there for an epic blizzard in the Northeast, except for one: cold air. This storm may pull a few tricks, though, and manufacture its own cold air through a process known as dynamical cooling.
In short, strong lifting of air on the northwest side of the storm, as well as cooler air aloft, may cause temperatures to drop just enough for heavy, wet, cement-like snow to fall in some spots. Computer models are vacillating on whether a switch to snow may occur in major cities like New York, Hartford, and even Boston, or if this will mostly be a windswept rainstorm.
Right now, a safe-ish bet is that up to a foot of snow is possible in higher elevations north of New York, the Berkshires of Massachusetts, and possibly the suburbs of the big cities.
However, there will be big surprises with this event, perhaps in the form of a sudden switch from heavy rain to wet snow. Power outages are likely in any areas where snow accumulates more than an inch or two, because of the weight of the snow.
Farther south, toward Washington, D.C., this storm is likely to cause a major, damaging windstorm, as the city will be between the strong low pressure area off the coast and an area of high pressure to the north and west. This will create a wind tunnel effect, in which the air rushes in between these two weather systems, with wind gusts forecast to be near or possibly above 60 miles per hour.
Here are the forecast peak wind gusts from the coastal storm. As this storm intensifies, it will produce a very large area of strong winds. High Wind Watches across much if the Eastern US, including the Baltimore-Washington metro & the central and southern Appalachians. pic.twitter.com/PTbr0PW8lL
— NWS Eastern Region (@NWSEastern) February 28, 2018
If you’re flying in or out of the D.C. area, including Baltimore and even up into Philadelphia, there likely will be significant delays on Friday, possibly lasting into Saturday. Delays are also likely at all New York City airports, as well as Hartford, Providence, and Boston, with the highest winds targeting Boston.
Some computer models are projecting wind gusts to near hurricane force (74 miles per hour) in eastern Massachusetts on Friday.
Lastly, there are signs of one, possibly two more intense nor’easters hitting next week. And guess what ingredient will be present at that time?
So, East Coast snow lovers, there’s still hope left even if you just get a bone-chilling rain and then some slush from this storm.