Winter Storm — Southern Grafton, New Hampshire

2020-12-17 · Southern Grafton, New Hampshire

Event narrative

Snow began after midnight on the 17th. Snow quickly became heavy as an intense band of snow moved into the area. As the band became nearly stationary over southern portions of Grafton County snowfall rates between 4 and 6 inches per hour were observed. A weakening trough aloft quickly brought an end to snow by mid afternoon. Snowfall totals were generally between 18 and 24 inches, with locally higher amounts approaching 3 feet in far southern Grafton County.

Wider weather episode

A modest low pressure system developed along the Gulf Coast on the 16th, with secondary development occurring off the Carolinas by the afternoon. An Arctic air mass was in place over New England as a strong high pressure anchored itself in the Saint Lawrence River Valley. Low pressure occluded early on the 17th and slowly tracked south of New England through the day. An intense band of heavy snow moved north into New Hampshire early in the morning on the 17th and remained nearly stationary into the afternoon. Snowfall rates of 4 to 6 inches per hour and total amounts pushing 3 to 4 feet were observed at the peak of the event. Dry air and a deamplifying upper trough limited the northward push of heavy snow, leaving a sharp gradient on the poleward edge of accumulating snowfall. Despite roughly 12 hours of snowfall, some observed amounts challenged 24 hour state snowfall records.

Source: NOAA Storm Events Database, event_id 926222. Narrative written by the NWS forecast office that issued the report.