What is a cryofront? A minimax curve for winter cold:
for each streak length k, find the coldest k-day window in the season
and report its peak daily high. This is a
Pareto frontier of cold—there was no longer cold streak without
allowing a higher ceiling temperature during that season.
Where a curve crosses 32°F,
that’s how many consecutive days the temperature never rose above freezing.
The bold line is the current season (Oct–Sep).
The dashed line (toggle “Last k days”) shows the
peak high over the most recent k days—a snapshot of right now.
More details…
How the Cryofront Works
Pick a number of days—say 7. Now look at every 7-day stretch during
the winter and ask: what was the highest temperature during that stretch?
The cryofront finds the 7-day stretch where that high was as
low as possible. That’s the coldest week of winter,
measured by how warm it got at its warmest.
Repeat for every streak length from 1 to 42 days and you get a curve.
At k = 1, the cryofront is simply the lowest single-day
high of the season—the day whose high temperature was the coldest.
As k grows, longer streaks inevitably include a warmer day, so
the curve rises. This tradeoff is a
Pareto frontier—you can’t find a longer cold streak
without allowing a higher peak temperature.
Where a curve crosses 32°F, it means the daily high
never rose above freezing for that many consecutive days.
Reading the chart
Each line is one season. The bold line is the current
season (updated as winter progresses). The x-axis is the streak length
in days; the y-axis is the peak daily high during that streak.
Hover over any point to see the exact dates of the cold streak.
The optional “Last k days” overlay
(dashed line) shows the maximum daily high over the most recent
k days, ending today. Today’s value is the high
temperature so far today—it may rise as the day
progresses, which is worth keeping in mind on a warm afternoon.
The “last k” line is always at or above the current
season’s cryofront, since the cryofront picks the
best window while “last k” is one specific
trailing window.
Daily highs only
All computations use daily high temperatures—one
value per day, representing the warmest temperature recorded that day.
The tool does not consider hourly data or intraday windows. A finer-grained
analysis using hourly temperatures could identify colder sub-day stretches,
but the daily-high framing gives a natural, calendar-aligned view of
sustained cold.
Seasons & data
A season runs from October 1 through September 30.
The current season’s curve updates throughout the year as new days
are added. When two equally cold streaks exist, the most recent one is
shown—so an ongoing cold snap always appears.
Weather data (daily high temperatures) comes from the
Open-Meteo
historical archive.