Saturday, December 23, 2017

A White Christmas - What is It?

sn't Christmas the only moment in the winter when we want snow?  Yes! What makes snow such an essential part of the Christmas landscape?  What makes a White Christmas so desirable?  In fact, in the U.S. there is WCA - White Christmas Anticipation. The website bigthink shows the map of the U.S., Canada and Europe for the percent chance of a White Christmas.

Did you know there's an official definition  of White Christmas?

From Wikipedia:  "In most countries, it simply means that the ground is covered by snow at Christmas, but some countries have more strict definitions. In the United States, the official definition of a white Christmas is that there has to be a snow depth of at least 1 in or 2.5 cm at 7:00 a.m. local time on Christmas morning, and in Canada the official definition is that there has to be more than 2 cm (0.79 in) on the ground on Christmas Day at 7 am".  

Our Environment Canada site has this chart - Amount of snowfall recorded in centimetres for major cities across Canada from 1955 - 2015.  Here are the Definitions of the columns:
  • % Chance:  probability of a white Christmas (snow on the ground of 2 cm or more on Christmas morning at 7 a.m. EST) for full period of 61 years
  • % Chance now:  for children today based on period 1996-2015
  • % Chance before:  for parents today when they were children based on period 1965-1984
  • Perfect Christmas:  snow on the ground of 2 cm or more on Christmas morning and snow in the air sometime Christmas day, i.e., a measurable snowfall on Christmas based on period 1955-2007
  • Snow depth now:  average depth of snow on the ground (cm) on Christmas morning from 1994 to 2015
At the bigthink site, it shows the maps of Canada, U.S. and Europe so you can see the distribution of White Christmases.  I hadn't realized how much of the U.S. has such a low probability of snow, and how much of Canada has a high probability of snow.  Our White Christmas distribution looks like a mirror reflection.

 And the forecast for this Christmas? Grimsby has a freezing rain changing to snow warning today - and a white Christmas is forecast.

Our pictures show last year's visit to the Guelph Arboretum on a very snowy day before Christmas.

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