Bigfoot takes on a Boston nor'easter. Image Credit: Kayana Szymczak/Getty Images

A major nor’easter will bring heavy snow and gusty winds to the northeastern megalopolis on Thursday, February 9, dropping at least a half-foot of snow across the most heavily populated region of the United States. The dose of intense winter weather will snarl travel and likely bring daily life to a halt through the beginning of the weekend. The heaviest accumulations are possible between New York City and Boston, where some locations could see a foot or more of snow by sunrise on Friday.

The catalyst behind the classic winter storm is a strong disturbance digging its way east across the country. The same system that will trigger the nor’easter brought snow and subzero temperatures to the Upper Midwest earlier this week; morning lows dropped lower than -20°F in North Dakota and Minnesota on Wednesday morning. The upper-level trough will cause a low-pressure system to develop at the surface in Virginia on Wednesday night. This low will quickly strengthen as it moves over the Atlantic Ocean and tracks parallel to the East Coast. It’s a scene that repeats itself every winter—one that snow lovers and winter haters alike are all too familiar with.

The Weather Prediction Center’s most likely snowfall forecast for the three-day period beginning at 7:00 AM EST on Thursday, February 9, 2017. Image Credit: Dennis Mersereau

The latest forecast from NOAA’s Weather Prediction Center calls for about half a foot of snow between eastern Pennsylvania through southern New England. The greatest chance for heavy snow stretches from northeastern Pennsylvania through eastern Massachusetts, where the most productive snow bands are expected to develop. Precipitation will begin on Thursday morning in the Mid-Atlantic and work its way north through the afternoon hours. The last of the snow should taper off on Friday morning in New England. It’s worth noting that there will be a relatively sharp gradient between having to crack out the shovel and a dusting on the grass—a boundary that’s likely to set up right along the Mason-Dixon Line. Precipitation will fall mostly as snow north of this line, while the storm will start as rain and could end as some snow to its south. It’s likely too warm for the Washington D.C. area to see more than a light coating of snow at the most, but its far northern suburbs could see a few inches from this system.

A weather model simulation of the nor’easter on Thursday morning, showing the heaviest snow bands on the northwest side of the storm. Image Credit: Pivotal Weather

Like so many nor’easters before it, this storm will play tug of war between unusually warm temperatures to the south and bitterly cold Arctic air to the north. The sweet spot for the heaviest snow will be where the cold air intersects with the area that has the highest moisture and the strongest lift, a region called the deformation zone. The deformation zone is almost always on the northwestern side of nor’easters, resulting in a swath of heavy snow that parallels the coast. Sometimes the heaviest snow bands set up far enough inland to miss the big cities, and sometimes they form right over the cities and result in those blockbuster blizzards that people remember for years.

The fact that the heaviest snow falls in such a narrow area makes forecasting nor’easters a tricky business. Warm air is a plague in East Coast winter storms; it can turn a potential snowstorm into an icy disaster or just a cold, miserable rain. A small eastward or westward shift—just one or two dozen miles—can render a snowfall forecast completely useless. This happened just last month during the significant snowstorm in the Carolinas and Virginia. The storm tracked a little farther inland than expected, allowing warm air to chew away at the snow and result in mostly ice around cities like Raleigh, North Carolina, while giving heavier snow to Greensboro, two hours to the west of Raleigh.

Temperatures have been a roller coaster leading up to this snowstorm, and that trend will continue soon after it leaves. It’s been so warm on the East Coast lately that some cities are easily setting daily high temperature records, including Washington D.C’s major airports on Tuesday and every airport around New York City on Wednesday. Temperatures behind the nor’easter will remain frigid during the day on Thursday and Friday as Arctic air drains in with the westerly winds behind the storm, aided by the icebox effect of having snow on the ground. Low temperatures on Thursday night will fall into the teens and single digits in areas with snow on the ground, and high temperatures on Friday will struggle to climb out of the 20s. Highs will quickly climb back above normal on Sunday and last through early next week, helping to melt any snow that falls from this hard-hitting but ultimately fleeting burst of winter.