Methodology

What "ice-out" means

There is no single official definition. For some lakes the recorded date is when the lake is essentially free of ice; for others it is when open water lets a boat run between certain landings; for the Nenana Ice Classic it is the moment moving river ice trips a clock. Each record keeps its own observer's definition, applied the same way year after year — that consistency, more than the definition itself, is what makes a record worth reading. It also means two lakes' dates are not always an exact like-for-like comparison, and we do not pretend otherwise.

Where the records come from

Minnesota

Minnesota DNR ice-out records — the deepest state archive of ice-out dates in the country, with decades of observations per lake.

New Hampshire

USGS Open-File Report 2010-1214 (Hodgkins, 2010), which collects historical ice-out dates for New England lakes; the Lake Winnipesaukee Ice-Out record as kept on Wikipedia; and the Squam Lakes Association's ice-out records.

Maine

The same USGS Open-File Report 2010-1214 is the backbone, with records reaching back into the 1800s for some lakes. It is extended through the current year with the Maine Bureau of Parks and Lands ice-out reports, published each spring.

Vermont

The Joe's Pond Association's Ice-Out Contest results — the association's own year-by-year table.

Alaska

The Nenana Ice Classic: the official site and the year-by-year record as kept on Wikipedia.

Where two sources cover the same lake and disagree on a year — different observers can be a day or two apart — we keep the earlier date. Each page lists its own sources at the bottom, so you can always check the record against the keeper.

How the usual, earliest, and latest dates are read

"Usually goes out around…" is the middle of the record: line every recorded date up by calendar day and take the middle one — the median. When a record has an even number of years we take the earlier of the two middle dates, so the usual date is always a date that actually happened on that lake.

Earliest ever and latest ever are read by calendar day across the whole record, whatever the year — a mark set generations ago still stands until some spring beats it.

Each lake carries one date per year. A lake gets a page only when at least five recorded years stand behind it — honest gaps over padded data.

What the in-season tracker does

In season — late winter into spring — lake pages carry one short line on where the current year stands: running early, late, or about normal for that lake. It rests on daily temperature readings from a weather station near the lake, set against the lake's own record. It is a progress note, not a forecast, and never a safety call. Off season, the line goes quiet.

The safety boundary