As the temperature increases in the Mount Washington Valley, so does the flooding potential for its many rivers. Since the annual spring warming trend has begun, residents keep a greater watchful eye on current weather conditions and forecasts. During this time, waterways overflow their banks in varying intensity while displaying tremendous force. This force can eventually result in widespread damage. Recent years have shown that the Mount Washington Valley has escaped the wrath of severe springtime flooding. However, it only requires a few elements to induce a situation to the contrary.
The severity and longevity of springtime flooding is not exclusively dependent upon whether or not there is deep snow on the ground. The fluctuation in temperature and the amount of rainfall received during March and April can greatly ease or enhance the melting process of the snow. For example, on April 1, 2001, an extremely rare and magnificent snow depth of 44 inches laid upon the ground in North Conway. Many meteorologists were very concerned about the potential of severe river flooding. If the temperatures were to spike into the 60s with occasional rainfall, the region would succumb to devastating river flooding. Fortunately, the temperatures huddled around 50 degrees and remained dry each day, which in turn prevented significant flooding.
Likewise with this current winter, the Mount Washington Valley usually receives high amounts of snowfall with very cold temperatures. One of the largest threats to the rivers of the region is the occurrence of ice jams. Flooding as a result of an ice jam is imminent when heavy rain and unusually mild conditions occur during spring. The heavy rain with rapidly melting snow causes frozen rivers to swell, which then forces the ice to break into large chunks. These chunks of ice flow downstream where they eventually pile up at a narrow passageway or obstruction on the river. When the ice jam is formed, water then overflows its bank at a very high rate.
A classic example of severe springtime flooding occurred during 1987. The temperature rose into the 50s during the beginning of March as a substantial snow pack laid prominent in much of New Hampshire and Maine. The water equivalent in this snow was 5 to 10 inches. Simultaneously, a low-pressure system, which originated in the Midwestern United States, moved slowly across New England. Southeasterly winds then developed a significant enhancement in precipitation over the White Mountains. Around 8 inches of rain accumulated in the region by the end of the storm.
In response to the snowmelt and record rainfall during March 1987, ice jams developed along much of the Saco and Androscoggin Rivers. An estimated 74.5 million dollars in damage, as well as one death, occurred in the state of Maine. As was the case during 1987, it only takes a few elements to produce severe river flooding, which in the future, could occur at a moments notice.