Halloween

This is a few days early, but today we're going to look at Halloween weather.

Temperature History

In recent years the average high has been 4°C and the average low is -4°C.

But look at 1984: a high of -18°C and a low of -24°C. Crazy. And that high temperature of -18°C was lower than the low temperatures of every other Halloween, except for 1991.

Another strange thing is that we haven't had a Halloween above 15°C since 1981. From 1897 through 1981 there were 9 of them, but there haven't been any since. And from 1880 to 1983 there wasn't a low below -15°C, but since then we've had three of them.

Lets take a closer look at recent history:

Recent Temperatures

The 1980s were my peak-trick-or-treating years. They all blur together, but I remember a lot of parkas - parkas tucked under costumes, parkas over costumes, and maybe even a balaclava one year?

Looking at the history, I guess it wasn't really that cold, but 1984 really was that cold. If I was ever forced to wear a balaclava it would have been in 1984. It is worth pointing out that it wasn't just Edmonton: Calgary's high and low were -16°C and -26°C. But just a few years earlier in 1981 both cities recorded 20°C on Halloween, which was Edmonton's warmest and Calgary's second warmest.

I'd said that the 30-year average high is 4°C, but that's not a great representation because the temperatures actually bounce around quite a bit. In the last 10 years we've had: 2 Halloweens around -5°C; 3 around 5°C; and 5 around 10°C. 

And the average low is -5°C, but the breakdown for the last 10 years is: 2 below -5°C, 2 at around -5°C, and 6 above (or right at) freezing.

So most of the time Halloween here is fall-like, with the occasional years edging into wintery. And just in the last 10 years we've been more consistently above 5°C (80%) than in the 1980s (70%) or 1990s (40%).

Precipitation History

This chart of precipitation is more complicated than I'd like, because it's showing a combination of data from Blatchford (solid lines) and the International (dashed lines), as well as for rain (blue) or snow (b&w). So that's why there are so many lines.

Halloween doesn't get precipitation very frequently, but when it does it's fairly evenly split between rain and snow.

1882 and 1999 are the big snow years at about 10cm, and then there were a few more in the 6-8cm range. And the last "big" rain years with over 2mm were back in the 1960s. 

Finally, Environment Canada has a measurement they call "Snow-on-Ground":

Snow-On-Ground

I've never used this before, and the data for snow depth is a little spotty, so I'm not quite sure how much faith to put in it. 

This only goes back to 1955, and in those last 60 years it looks like 2000-2006 was the real stand-out for most consistently snowy: 6 of those 7 years had 2cm or more snow on the ground. And I honestly don't recall that at all. But since then none of the years show any snow on the ground.