Barometric Pressure Forecast for Merrimack, New Hampshire
Barometric pressure forecast for Merrimack, New Hampshire — in the Merrimack River valley where cold air dams against the White Mountains and the coastal front decides the forecast. See current barometric pressure and what it means for weather-sensitive people.
Download Pressure Pal to track barometric pressure and get migraine alerts for Merrimack and your area.
Pressure and weather in Merrimack
Merrimack occupies the floor and low terraces of the Merrimack River valley in Hillsborough County, between Nashua and Manchester, with the Uncanoonuc hills to the north and the coastal plain about thirty miles east. Southern New Hampshire's winter difficulty is that it sits where two boundaries frequently intersect. The first is cold-air damming, when high pressure over Quebec and the Maritimes pushes dense cold air southwest along the eastern flank of the Appalachians and it pools in valleys like this one; the surface stays below freezing while milder air overruns it aloft, and the result is prolonged sleet and freezing rain rather than snow. The second is the coastal front, a sharp low-level boundary that often sets up between the shoreline and the interior and marks the difference between plain rain and a foot of snow, sometimes within fifteen miles. Neither of these is visible in the depth of the low, which is why a barometric pressure forecast alone will not tell you what falls from the sky here, though the falls in current barometric pressure during a well-organised coastal storm are substantial and prolonged. Behind departing systems, arctic highs bring strong rises with clear skies and biting northwest wind. Summer is convective, with afternoon thunderstorms rolling southeast off the higher terrain and a mostly level trace. A barometric pressure forecast for Merrimack matters most from December through March.
What this means for you
Can barometric pressure cause headaches? Damming events are worth logging carefully, because they can hold pressure and temperature nearly constant for a day or more while conditions feel oppressive. That combination looks different in a log from a fast-moving storm. Use Pressure Pal as a migraine tracker app and watch pressure change today whenever a coastal low is expected.