Flood in Carroll County, New Hampshire

Severe flooding occurred in Bartlett and upstream in Hart's Location, New Hampshire on December 18th. The flooding was the result of heavy rain and rapid snowmelt along the steep slopes of the south facing mountains around Bartlett. The combined runoff from rainfall and snowmelt is estimated to be around 10 inches. The steep terrain and frozen ground resulted in very rapid runoff with flash flooding occurring along every small stream and brook in the region. The USGS river gage at Bartlett went from 3 feet at 9 PM on the 17th, to 13.8 feet by noon on the 18th. The discharge was measured over 25 kcfs, which has an annual chance exceedance of 1% to 0.2%, otherwise referred to as a 100 to 500 year flood. The river stage reached was the 3rd highest on record, and a foot below that reached during Irene in 2011. The hardest hit areas were the confluence of the Saco River, the Rocky Branch and at the confluence of the Ellis River. Route 302, a main thruway to the region closed from Glen to Jericho due to severe flooding. West Side Road was flooded along with numerous homes and camps. In Bartlett, the flood waters flooding River Street up to Route 302. Additionally, several local road closures and washouts were reported along the Saco and other small streams and brooks. There was significant damage to a campground in Bartlett and another in Glen Ellis.

Low pressure began organizing in the Gulf of Mexico on the 16th, setting record low sea level pressures as it traversed the Southeast through the 17th. Strong high pressure over the North Atlantic created a deep southeasterly flow that drew warm air into New England ahead of the approaching storm. By the time precipitation arrived on the evening of the 17th, temperatures were warm enough for rain everywhere except the highest peaks. Early on the 18th a shortwave trough was approaching from the Great Lakes and led to rapid deepening of the low pressure as it paralleled the Eastern Seaboard. Even as the center of the storm remained near Chesapeake Bay on the morning of the 18th, a strong low level jet had developed and winds began to gust in excess of 50 mph well inland from the coast. Damaging wind gusts continued into the afternoon. Thousands of customers lost power due to falling limbs and downed wires. The anomalously warm air mass also led to intense rainfall rates beginning on the evening of the 17th, which continued into the 18th. Upsloping winds also enhanced precipitation along the southeast facing slopes of the White Mountains. Widespread 3 to 4 inches of rain fell, with isolated pockets of 6 to 8 inches. This fell on top of snow that was ripe from previous rainfall about a week earlier. An additional 2 to 3 inches of snow water equivalent was likely added to rainfall runoff. Numerous road washouts and road closures occurred due to flash flooding and fast responding small stream and tributaries. Localized moderate to major flooding occurred along mainstem rivers with the majority of New Hampshire Rivers outside of the mountains only reaching minor flood stage.