Forecasters are warning that a narrow coastal boundary could make the difference between a modest plowable snow and a backbreaking cleanup in southern New Hampshire. As a strong winter storm spreads across the region from Sunday into Monday, small shifts in that coastal front’s position may cause snow totals to double from one town to the next, leaving residents and road crews to plan for a wide range of outcomes.
The setup features moist ocean air colliding with arctic cold just inland, a classic recipe for sharp gradients in snowfall. Where that dividing line wobbles, bands of intense snow can park over the same communities for hours, while areas only a few miles away see lighter, fluffier flakes and lower totals. For drivers, homeowners and emergency managers, understanding how that front behaves will be as important as watching the overall storm track.
Why this storm is primed to overperform in parts of New Hampshire
The broader storm is robust enough that much of New Hampshire is already projected to pick up more than a foot of accumulation, with the heaviest snow focused from Sunday afternoon through Monday evening. Forecast graphics show Snow spreading across New Hampshire as temperatures hover near 30 degrees, a sweet spot that supports efficient accumulation on untreated roads and sidewalks. With that baseline in place, any localized enhancement from the coastal front will be layered on top of already significant totals.
Earlier this weekend, meteorologists highlighted that a significant winter storm would bring over a foot of snow to much of New Hampshire between Sunday and Monday, with the core of the event expected through much of Monday as the system deepens. That expectation is reflected in regional maps that show widespread double digit projections and emphasize that this is not a marginal event that depends on a last minute shift to snow. Instead, the question is how much higher some communities climb above that one foot mark once the coastal front sharpens the contrast between inland and shoreline zones.
How the coastal front forms and why it matters
The coastal front at the heart of this forecast is essentially a narrow boundary where relatively mild, moist marine air from the Atlantic meets much colder arctic air just inland. Forecasters describe how this will meet up with that arctic air over the interior, and just on the cold side of this feature, they identify what they call the coastal front, a zone that can focus lift and moisture into a tight band of heavier snow. In televised briefings, they have walked through how this boundary sets up over southern New Hampshire, using radar and model simulations to show the sharp line between lighter and heavier returns.
As the storm matures, the contrast along that front can intensify snowfall rates, turning a steady light snow into a burst of near whiteout conditions for towns that end up on the cold side of the boundary. One detailed explanation notes that as this coastal front collapses back toward the ocean closer to midnight, the snowfall rates start to lessen, underscoring how the front’s position and eventual retreat control both the timing and intensity of the heaviest bands. That evolution means some communities may experience only a brief window of intense accumulation, while others sit under the enhanced band for much longer and see totals spike.
Where the sharpest snow gradients are likely to set up
In southern New Hampshire, the most dramatic differences are expected in a corridor running from the immediate shoreline inland toward the Merrimack Valley and into the interior hills. Forecast maps show Snow moving into New Hampshire for the second half of the weekend and on Monday, with many spots projected to see more than a foot, but they also highlight a narrow stripe where totals jump quickly over short distances. That band is tied directly to the coastal front, which tends to align roughly parallel to the coastline before wobbling inland or seaward as the storm evolves.
To the south, forecasters tracking Greater Boston have warned that the same system could deliver 20 or more inches of snow, especially as a trough moves in from the north Monday between 7 and 9 a.m. while the low deepens across the Gulf of Maine and moves toward the Canadian Maritimes. That evolution over the Gulf of Maine helps sharpen the pressure gradient and can tug the coastal front slightly inland into southern New Hampshire, increasing the odds that communities just away from the immediate shoreline end up in the bullseye for the heaviest band. The result is a patchwork of totals where one town may measure close to 2 feet while another, only a short drive away, struggles to reach a foot.
Timing the heaviest snow and the coastal front’s collapse
For residents trying to plan travel or snow removal, the timing of the coastal front’s strongest influence is as important as its location. Video forecasts for New Hampshire indicate that Snow will fall, heavy at times, through 2 a.m. tonight, with snow turning lighter in intensity during the predawn hours of Monday morning as the front weakens and the system begins to pull away. That transition period, when the coastal front collapses back toward the ocean, is when the most dramatic snowfall rates are expected to taper, even if lighter snow continues into the day.
Regional discussions also point out that Monday between 7 and 9 a.m., as the trough drops in from the north and the low intensifies over the Gulf of Maine, the storm’s structure will favor lingering bands on the northwest side of the circulation. In practice, that means some inland areas of southern New Hampshire could still see moderate snow during the Monday morning commute, even as coastal communities begin to see improvement. The National Weather Service office that covers the region has highlighted this evolution in its winter storm warnings, noting that hazardous travel will persist while the front is active and that conditions will only gradually improve as the banding breaks apart.
Forecast confidence, model spread and what residents should do
Even with high confidence in a major storm, the exact placement of a coastal front is notoriously difficult to nail down more than a few hours in advance. Meteorologists have been candid that the broad challenge is figuring out how winter storms will behave when there are sharp temperature contrasts, a point that came up in a recent Q&A where a reader named Tom asked about snowstorm behavior in cold weather. That uncertainty is magnified in a setup like this one, where a few degrees of temperature change at the surface or a subtle shift in wind direction can nudge the front inland or offshore and dramatically alter who sees the highest totals.
Local forecast offices are leaning on high resolution models and real time observations to refine their projections as the storm unfolds. The National Weather Service has posted the latest snow accumulation estimates, warning that some parts of New Hampshire could get close to 2 feet and that heavy snow and strong winds will create extremely dangerous travel conditions. Their regional page for the area underscores the risk of blowing and drifting snow, particularly where the coastal front enhances totals and produces deeper drifts along exposed roadways and open fields.
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