The year in Calgary, month by month
All the figures are Calgary's: 445.4 millimetres of precipitation a year over 114.0 days, 138.7 centimetres of snow and 2,396.3 hours of sunshine. The scoring crosses three things: how much water falls, how much light there is and how far the temperature can be trusted.
Almost every winter destination is planned around one question: how cold will it be. In southern Alberta that question has no answer, and not for lack of data, but because the margin is so wide that the average tells you nothing.
Calgary's January mean is −7.6 degrees. But the same station has recorded both 17.6 degrees and −44.4 in that same month: 62 degrees of range inside a single box of the calendar. The cause has a name.
01 From minus nineteen to twenty-two in sixty minutes
The extreme case is documented and it is the national record. On 10 January 1962, at Pincher Creek, some 200 kilometres south of Calgary, the temperature rose from −19 to 22 degrees in a single hour. That is 41 degrees in sixty minutes, close to two-thirds of a degree per minute.
It was not a one-off. The same town recorded a rise of 25.5 degrees in an hour on 6 January 1966, from −23 to 2. And in Calgary swings of 20 to 30 degrees within a few hours are not considered unusual.
Frequency is what turns the phenomenon into a travel factor. Calgary records some 25 chinook days per meteorological winter, December to February. That is, one day in three or four.
02 How the chinook works
The mechanism is that of any föhn wind and here it shows with particular clarity. The air arrives from the Pacific loaded with moisture, hits the Rockies and has to rise. As it climbs it cools, and as it cools it releases its water as rain or snow on the western flank.
On the other side the opposite happens. The air, now dry, descends the eastern flank, compresses as pressure rises and warms. And because it has lost its moisture, it warms faster than it cooled on the way up. That mismatch is the whole trick.
The sign in the sky is unmistakable and has a name of its own: the chinook arch. A cloud band with a straight edge stops over the range and leaves a strip of clear sky beneath it. When it appears, the temperature is about to rise.
03 January: 17.6 degrees and 44 below zero
Calgary's figures describe the situation well. January's average high is −1.5 degrees and its average low −13.5. So far, an ordinary continental winter. The problem is the extremes: a record high of 17.6 degrees and a record low of −44.4, both in January.
February holds the city's absolute cold record, −45.0 degrees, and at the same time a record high of 22.6. And December, with an average high of −0.4, has reached 19.5.
The practical consequence for a trip is twofold. The first is that you have to pack for both scenarios, because they can happen in the same week. The second is that the snow on the ground is not reliable: a chinook can strip the province's south of its cover in a day.
04 And the wettest month is June
The other figure that throws people is in the summer. Calgary's wettest month is neither July nor August: it is June, with 112.7 millimetres over 14.5 days of precipitation. Both figures are annual maxima.
The comparison puts it in scale. July receives 65.7 millimetres, August 53.8 and September 37.1. So June receives almost double July's total and three times September's, out of an annual total of 445.4 millimetres over 114.0 days.
June is also the month when many people plan their Rockies trip, on the grounds that the days are long and the crowds have not yet arrived. The days are long, true — 269.9 hours of sunshine — but they are also the wettest of the year.
The year's four stretches
From 10.0 to 12.5 millimetres a month and 16.3 to 16.9 centimetres of snow, with sunshine between 114.0 and 144.6 hours. Means run from −7.6 to −5.9 degrees, but the real range is enormous: January has recorded both 17.6 degrees and −44.4.
23.8, 22.9 and 9.6 centimetres of snow: March and April are the year's two snowiest months, ahead of any winter month. Rain climbs from 17.7 to 61.1 millimetres and sunshine from 177.2 to 249.4 hours.
112.7 millimetres over 14.5 days. The year's absolute maximum in both columns and almost double July's. It has 269.9 hours of sunshine and highs of 19.7 degrees, but it is the worst month for walking badlands or mountains.
65.7, 53.8 and 37.1 millimetres, with sunshine between 314.1 and 207.0 hours and highs from 23.5 to 18.3 degrees. Rain drops month by month and snow disappears entirely in July and August.
05 The snow does not come when you expect
There is a third inversion, and it concerns snow. Calgary's snowiest month is March, with 23.8 centimetres, followed by April with 22.9. Both exceed November, with 18.8, and January, with 16.6.
In other words: it snows less in the depths of winter than at the end of March. The reason is the same one that produces the chinook: deep winter brings cold, very dry continental air, with only 10.0 millimetres of total precipitation in January, while spring brings moister air that still falls as snow.
For a winter trip that means April is still a snow month in the province's south, with 22.9 centimetres and average lows of −1.9 degrees, and that the mountain ski season holds far beyond what the calendar suggests.
06 How to choose the month
If you can go only once, go between July and September. July gives 314.1 hours of sunshine — the year's maximum — and average highs of 23.5 degrees; August, 284.0 hours and 53.8 millimetres; September, 207.0 hours and only 37.1 millimetres over 8.3 days.
Of the three, September best combines little rain with enough warmth, and it is also the least crowded. July is the brightest and warmest; August sits in between.
And if you travel in winter, do it knowing the plan can change twice in a week. With some 25 chinook days a season, the odds of catching one are high, and with it come twenty degrees of warming and ground stripped of snow. It is awkward for planning and it is exactly what makes this place different.
