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Weather Note for November/December/January: Neither rain nor warmer temperatures are a problem for compressor-cooled rinks during the short daylight hours of November, December, and January. While it's raining the ice is fine, underneath a thin layer of water, which freezes as soon as it stops raining. And warm weather in winter is not necessarily because of global warming: see our late-November Weather Data 1940-2011. It's the angle of the sun that matters.
posted March 04, 2008
The angle of the sun in March is already high enough that it fights the ice, very successfully. Here's a graph to show how much lower the temperature has to be in March to counteract that sun angle. March temperatures are seldom cold enough to keep the ice skateable. And energy costs go through the roof.
Our weather researcher, Corey Chivers, has created a research presentation that you can download. Download the pdf version (2.7MB), or the powerpoint version (4.4MB). You can also download the technical background paper.
Here are some observations from March 2008 that support this anaylysis: Rink Conditions March 2008.
*Note -- the graph below shows hard-ice temperatures at high noon. But in the morning and from 4 pm onward, hard ice is maintained at higher temperatures - 10-12 degrees celsius.
posted October 21, 2008
Recommendation: Conform the rink season to the angle of the sun. Based on over 10 years of tracking, the outdoor rink season should be early November to the first Sunday in March.
Comments: In the most recent (2006/07) rink season most (21) of the city-run rinks which we tracked did not open until December 9. Three rinks opened on November 25, December 2 and December 3 respectively. Two other rinks did not open until January due to delays in construction.
December 2006 was unseasonably warm and served as an instructive experiment on the effects of October/November-like temperatures on compressor-run outdoor ice rinks. Taking Dufferin Rink as a sample rink: Toronto’s December temperatures ranged from 0°C to plus 13°C. Throughout December there were no days when the rink had to be closed. In January the temperatures ranged between minus 12°C and plus 11°C. The sun was still low enough that there were no days when the rink had to be closed, even on sunnier days. In February the temperatures were, for the most part lower (ranging from minus 13°C to 0°C). Yet staff had to close Dufferin Rink by 1 pm on 3 days due to soft and slushy ice. In March this became even more pronounced with temperatures ranging from minus 20°C to plus 15°C – but 6 days of afternoon rink closures (often on cold days). Since the rink closing date was March 18, six closures actually represent 33% of the month closed during peak hours.
The angle of the sun in the late fall and early winter makes for dreary days that could happily be spent skating regardless of temperature (anywhere under 18°C) or clear skies (low sun). The compressors are designed to keep the ice frozen and are very well suited to countering the force of higher temperatures. But they are unable to counteract the effects of higher sun. Another example: on November 29 the ice at Harbourfront Rink was in perfect condition at plus 16°C, with over a hundred skaters when we visited, and no puddles. Similarly on December 17 when the high was plus 13°C and it was mostly sunny, the rink at Dufferin was in perfect condition, and full of skaters. Compare: Dufferin Rink staff were forced to shut down the rink during peak hours on March 7 on a sunny day when the high was only minus 6°C. The chart below demonstrates the increase in rink closures over the late winter months, and the fact that this increase happened despite overall lower temperatures.
Using the average daily temperatures that Toronto experiences between November and the end of March, along with the angle of the sun at noon hour of each day, the melt rate of the surface ice was calculated. The following chart illustrates how under average seasonal conditions, outdoor rinks work best from early November until the end of February.
Click on the graph for a larger image.
When these rinks were built, they had a fixed season: November 15 to the end of February. After amalgamation, City Council began to shrink the season, so that in 2001 most rinks didn't open until December 22. Then the season was increased again, but at the wrong end. In 2006/2007, and 2007/2008 the rink season was about the same length as the original rink season (106) days. But because so much of the season was in March, the ice was often bad and rink usage was very low.