Independent New Hampshire Journalism · Northfield, NH

Lake Winnipesaukee’s Ice-Out Record Goes Back to 1887. The Four Earliest Calls Have All Come Since 2010.

A U.S. Geological Survey compilation of 122 springs on New Hampshire’s largest lake, 1887 through 2008, puts the average ice-out near April 20 and finds only two in March. Since 2010 the lake has been declared open in March at least four times, and the earliest on record through 2026 is March 17, 2024.

Every spring someone has to decide when the ice is gone from Lake Winnipesaukee. The call comes from pilots at Emerson Aviation in Gilford, who watch the lake from the air. Ice-out is declared when the lake is clear enough for the cruise ship MS Mount Washington to reach all five of its ports: Alton Bay, Center Harbor, Meredith, Weirs Beach and Wolfeboro.

The declaration does not mean every piece of ice has melted. When Emerson Aviation called ice-out on April 12, 2026, it said ice remained in Moultonborough Back Bay and Winter Harbor, but that the ice “would not impede the MS MT Washington if it were to sail today,” as NHPR reported. The date marks the unofficial start of spring in the Lakes Region and the beginning of boating season. It is also one of the longest-running records of winter in New Hampshire, and a federal agency has published it year by year.

What the federal record shows

In 2010 the U.S. Geological Survey published Historical Ice-Out Dates for 29 Lakes in New England, 1807–2008, an open-file report by Glenn A. Hodgkins. Table 29 covers Lake Winnipesaukee: 122 years of record, from 1887 through 2008, with no missing years. The report lists the observers as the New Hampshire Office of Vacation Travel, Harry Daniel, Arthur Marshall, Bob Aldrich, the Lakes Region Association, the Classic Journey Company and winnipesaukee.com. Its note on the definition says ice-out for most years “is thought to have been the earliest date of open navigation for the MS Mount Washington on its regular route, except for Meredith Bay.”

The report gives each date as a day of the year, with Jan. 1 as day 1. Granite State Report converted those numbers to calendar dates. Across the 122 years, the average fell on day 110, which is April 20 in a common year. The latest ice-out was May 12, 1888. The earliest was March 28, 1921, followed by March 30, 1946. Those were the only two March ice-outs in the federal table. Another 107 came in April and 13 in May. The last May ice-out in the table is May 2, 2001; the one before that came in 1972.

The record does not move in a straight line. Averaged by decade, ice-out drifted from April 24 in the 1890s to April 17 or 18 in the 1920s and 1950s, then slid later again. The 1970s averaged April 25, the latest full decade in the table. The 1980s and 1990s both averaged April 17.

Comparing longer stretches smooths out the swings. The first 30 years of the table, 1887 through 1916, averaged day 112.3, or April 22. The last 30, 1979 through 2008, averaged day 107.5, or about April 18. That is a shift of about five days. The same report carries Lake Sunapee, with records from 1869 kept by the Argus Champion and the Sunapee Town Office. Over the same two 30-year windows, Sunapee’s average moved from April 26 to April 19, about seven days.

After 2008, the March calls

The federal table stops at 2008. Later dates come from Emerson Aviation’s declarations as news outlets reported them. In an April 2021 column, David Brooks of the Concord Monitor’s Granite Geek blog went through the ice-out list kept on winnipesaukee.com. He found that the three earliest calls to that point were March 18, 2016, March 23, 2012 and March 24, 2010. He put the average for the 2010s at April 6, “by far the earliest of any decade,” against April 17 for the 2000s.

Brooks’s decade averages come from a different compilation than the federal one, and for the same decades they differ from Granite State Report’s figures by up to two days. This article does not merge the two lists. Brooks also warned that ice-out “is a subjective call” and that comparing results over time “is questionable.”

The record fell again on March 17, 2024. Matthew Gianunzio, a pilot and flight instructor at Emerson Aviation, made the call that Sunday, NHPR reported in a story republished by WBUR, one day earlier than the 2016 mark. Dave Emerson, who owns the company, told NHPR he had called ice-in on Feb. 9 that winter and that the ice began melting just 24 hours later, something he said he had never seen. Ice-out came on April 16 in 2025 and April 12 in 2026. In its April 2026 report, NHPR wrote that the four earliest ice-out days had all come in the previous sixteen years.

What one date can and cannot show

Ice-out is one person’s judgment on one day, and the people making it have changed. The USGS report says ice-out definitions “can vary over time and between observers” and that the exact definition “is not known with confidence in most cases.” It did not estimate missing years or adjust the Winnipesaukee observations.

The longer view comes from a 2005 USGS fact sheet by Hodgkins, Ivan C. James II and Thomas G. Huntington, which summarized their study of the same 29 lakes. They found that ice-out had become significantly earlier in New England since the 1800s. Between 1850 and 2000 the date moved 9 days earlier in northern and mountainous areas, mainly northern and western Maine, and 16 days earlier in more southerly locations. About half of the year-to-year variation, the fact sheet says, is explained by March and April air temperatures. Based on that relationship, the authors estimated late-winter and early-spring warming of about 2.6 degrees Fahrenheit since 1850. The fact sheet adds that changes in ice-out timing can affect lake conditions such as how fast oxygen levels change through the summer, and parts of the food chain.

Winnipesaukee’s federal series begins in 1887, not 1850, so it cannot answer the 1850 question by itself. What the lake’s own record does show is a modest drift through 2008 and a run of March declarations after it. Before 2010, the federal table had two March ice-outs in 122 years. In the springs since, the lake was declared open in March at least four times.

Granite State Report covered ice-out as part of a wider look at the state’s climate in Warming Winters, Rising Waters: How Climate Change is Reshaping New Hampshire.

— Granite State Report

Fact check

Editor’s note. Ice-out dates for 1887 through 2008 are drawn from U.S. Geological Survey Open-File Report 2010–1214. Findings on New England’s lakes are drawn from USGS Fact Sheet 2005–3002. Dates after 2008 are drawn from NHPR (including a story republished by WBUR), InDepthNH, the Boston Globe, the Concord Monitor’s Granite Geek blog and NH Healthy Climate. Averages, counts and calendar conversions are Granite State Report arithmetic from the USGS tables.

Corrections: Granite State Report corrects verified errors promptly and appends a dated note identifying what changed and when. The corrections policy and the corrections register are public, and correction notes are never removed.