Winter Storm — Northern Grafton, New Hampshire

2020-12-17 · Northern Grafton, New Hampshire

Event narrative

Snow began before sunrise on the 17th. The heaviest snowfall moved into areas south of Franconia Notch by mid morning. Snowfall rates exceeded inch per hour in the heaviest snow, but dry air to the north and weakening lift with increasing latitude left a sharp gradient in storm totals north of the notches. Snowfall totals ranged from 12 to 18 inches in the southern White Mountains westward to the Connecticut River, but only 3 to 6 inches north of the notches to Littleton.

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 926220. Narrative written by the NWS forecast office that issued the report.