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Lake Winnipesaukee Ice-Out, Analyzing The 127 Years Of Data — To Celebrate Yesterday’s, i.e., April 17, Ice-Out For 2013.

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by
Anura Guruge


Yesterday was ice-out on Winnipesaukee.

Historic ice-out data going back to 1887 is available at winnipesaukee.com. So that is 127 years worth of ice-out dates.

I, for the first time this year, had a couple of hours off! I am waiting for Amazon to publish another Kindle book. So, I wanted to indulge myself while I waited (patiently) and given that I am strange crunching data is an indulgence.

So, I did some quick analysis. One thing I quickly noticed is that people don’t pay enough attention to LEAP YEARS. In terms of days into the year, March 23 & March 24 are both 82 days independing on whether it is a leap-year or not. So to say that last year was the earliest ice-out is wrong in a way.

I copied and pasted, did some concatenations and replaces, used (the now unsupported but still available) =DATEDIF Excel function and =WEEKDAY and voilà. [No, I never type in data.] Yes, I had to hand calculate the 13 pre-1900 years since Excel dates only start as of 1900 — but I used the Windows 7 calculator that can calculate dates going back to 1500 and one of my perpetual calendars. So, I ended up with a sortable Excel spreadsheet — which looked like this, after I had sorted it by data distribution. All calculations are based on days into the year, starting January 1 of each year.

Click to ENLARGE. This was towards the end when I was calculating date distribution.

Click to ENLARGE. This was towards the end when I was calculating date distribution.


Ice out dates over the last 127 years. Click to ENLARGE.

Ice out dates over the last 127 years. Click to ENLARGE.


The day of the week that ice-out has occurred -- Thursdays the most prevalent. Click to ENLARGE.

The day of the week that ice-out has occurred — Thursdays the most prevalent. Click to ENLARGE.


Distribution of ice-out day across a 51-day spread between March 23 and May 12. Click to ENLARGE.

Distribution of ice-out day across a 51-day spread between March 23 and May 12. Click to ENLARGE.


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About Anura Guruge

See 'The Blogger' on my https://nhlifefree.com/ blog.

2 responses to “Lake Winnipesaukee Ice-Out, Analyzing The 127 Years Of Data — To Celebrate Yesterday’s, i.e., April 17, Ice-Out For 2013.”

  1. caroyn says :

    Anura,
    Interesting look in to the data. I was thinking of taking this further by looking into lake levels and precipitation in the outlier years. Visually it looks like the 95% confidence level around the mean no. of days is 95 and 115. Your excel files give me the dates below 96 days but not the dates above 115. i can go to your original source but will have to replicate your Leap Year adjustments. Would you be willing to share your data? Thanks, Carolyn

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