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The fourth nor'easter in just three weeks is taking shape across the Mid-Atlantic states.

The storm is expected to become the biggest late-March snowstorm on record from Washington, D.C. to New York City.

The fact that the storm is hitting on the first full day of spring is twisting the metaphorical knives in the backs of millions who are weary of shoveling snow, enduring power outages, and facing more travel disruptions.

This storm has the potential to shatter March snowfall records in Washington, D.C., Philadelphia, and New York, where up to a foot or more of snow is possible. Some spots in southeastern Pennsylvania and New Jersey could approach 2 feet, if computer model projections on Tuesday afternoon prove to be correct.

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In a forecast discussion posted online, the National Weather Service forecast office for the Philadelphia area used particularly strong language to describe the storm threat, saying forecasters were concerned about "major" to "extreme" impacts in the Philadelphia area, along Interstate 95 north to Interstate 80, on Wednesday afternoon and Wednesday night.

The snowstorm will result from an area of low pressure taking shape in the Carolinas on Tuesday. The storm will intensify as it moves off the Mid-Atlantic coast, throwing copious amounts of moisture from the Atlantic Ocean and Gulf of Mexico inland, where the air is cold enough to support snow.

The heaviest snow will fall in narrow bands just 10 to 20 miles wide. These are known as "mesoscale bands," since they are so localized, and they form where the strongest atmospheric lift is located.

Within such bands, snow could fall at up to 2 inches an hour or greater, whereas in between them, it will be snowing at slower rates, bringing far lower accumulations.

The heaviest snows are forecast for the Mid-Atlantic region, with considerable uncertainty about whether the higher snow totals will reach New York City and Boston, as computer models suggest a storm track further offshore than previously thought.

Even so, this will still be a major event for the I-95 corridor. It is also a prime example of what can happen when highly amplified weather patterns are established and are exceedingly slow to break down.

Let's face it -- the atmosphere is stuck in a rut, with the jet stream, the highway of fast-flowing air at about 35,000 feet -- setting off one nor'easter after the other as if someone forgot to hit the "off" switch.

Unlike the past three storms, though, this one is not expected to deliver its most severe impacts to the Boston area, but rather focus on Washington, Baltimore, Philadelphia, Wilmington, and central New Jersey.

It won't take much more than a foot of snow to set all-time snowfall records for this late in the month of March in New York and Philadelphia, both of which are within reach if the storm tracks close enough to the coastline to bring the heaviest snow to these areas.

The latest nor'easter, so named because the winds in such storms blow predominantly from the northeast, is occurring at a time when the overall climate is warming due largely to human activities, such as burning fossil fuels for energy. Therefore, it might seem paradoxical to have so many late-season snowstorms.

However, in a way, this repetitive fusillade of snow events may be what global warming looks like, for two main reasons.

Firstly, it will still snow in a warmer world, and there has been a well-documented increase in heavy precipitation events during the warm and cold seasons across the U.S., tied to the atmosphere's ability to hold more moisture as air temperatures increase. Therefore, when it snows, the odds could gradually favor heavier snowstorms, rather than moderate ones.

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Second, some researchers have been noticing an increasingly common tendency for weather patterns to get stuck in place, as large north-to-south undulations in the jet stream are slow to break down, thereby causing extended periods of extreme weather.

The physical mechanisms behind jet stream tendencies are not yet well-established, but many of the most severe weather extremes in recent years have been associated with such stuck weather patterns.

In addition, there is also some statistical evidence linking rapid Arctic climate change to increased snowstorm activity along the East Coast during the mid-to-late winter months.

As for this particular storm, though, one consolation is that the snow will melt far faster under the spring sun than it would've had this nor'easter parade occurred in January.

Also, you might not want to hear this, but there are some signs of a fifth nor’easter potentially forming next week, soon after the snow from this one has melted.

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