As I write this column, November is about to claim the calendar. But who would guess it given the past few weeks’ weather? It’s been so mild that the spring peepers began peeping again. Until just a few days ago, foliage remained vivid, and was still on the trees! Ocean temperatures stayed swimmably cool, not frigid. Sunshine is up, rainfall is down. (Ha!)
To demonstrate how unusual this mild spell has been, I’m going to summon my favourite weather graph, the “temp-precip” chart. On this grid, temperature runs horizontally, while precipitation (rain plus melted snow) goes vertically. Every point on the chart, like 20 °C and 200 mm, or -4 °C and 50 mm, represents a possible temp-precip combination, and many of those temp-precip pairs might actually occur somewhere. However, the long-term average temp and precip values for Ingonish (and much of Victoria County) through the course of the year fall only on the blue loop. Extraordinary!
Let’s begin in January, whose average temp and precip for Ingonish are -5 °C and 185 mm; they are marked with a blue dot beside the label “Ja”. From there, the weather follows the blue loop counter-clockwise. February’s and March’s temp-precip pairs aren’t far from January’s; and after April’s precip bump, we slide down and right into the drier, warmer summer months. In late summer we take the sharp curve up and left to moister, cooler temps through the autumn months and back to January. At any given day of the year the weather knows where it’s going next - it’s following the blue loop. And by referring to the blue loop, we can guess the weather’s next move! (Speaking in terms of long term averages, of course.)
If you averaged all the temps and all the precips along the blue loop for a year, you would get a temp-precip pair of 6.3 °C and 145 mm. That’s the green dot on the chart. Since it’s green and it represents Ingonish’s annual mean temp and precip, it is called the mean green dot. The mean green dot represents all the points of the blue loop averaged up and then shrunk down to a single point.
So Ingonish’s weather travels along its blue loop, orbiting its mean green dot once each year. It orbits in the chart’s two-dimensional “temp-precip space”, like earth orbiting the sun in 3-D “physical space.”
Whereas gravity and inertia keep the earth in orbit around the sun, the main force shaping the weather’s orbit turns out to be…. earth’s orbit itself! Cape Breton cannot remain at 6.3 °C all year because we receive different amounts of solar energy at different points in earth’s orbit, and those differences stretch our weather orbit into the -5 to + 19 °C range you see on the chart. In a sense, then, the blue loop is earth’s orbit, plotted in weather space rather than physical space!
Anyway, see those scattered red dots in the chart? They are Ingonish’s temp and precip values for 2017, for the months of January through October. The upper-leftmost one shows the January 2017 mean temp of -3.5° C, and total precip (rain plus melted snow) of 233 mm. Compared to the long term January averages on the blue loop, January 2017 was somewhat wetter and a bit warmer than the long term January average.
The dots for February and March 2017 landed close to their long term averages. Then things went wacky for two months - April was dry, but May quickly made up that deficit, going right off the top of this chart.
But the chart’s most remarkable feature is the group of temp-precip pairs for June through October, in the lower right. Precip in every one of these months was much below normal, while temps were warmer than normal in all but August. It appears that the weather has been derailed from its normal route, and we’re mired in dry, warm weather at the bottom of the graph.
Delightful as our weather’s autumn dalliance has been, earth’s orbit is sure to regain control. In fact, I’ll go out on a limb and boldly predict that soon we will make that turn on the graph and head towards wetter and cooler conditions more typical of year’s end!
Monthly temperature and precipitation data for Ingonish through the cycle of the year. The blue curve shows long term average values. Red dots are 2017 averages for each month (through October). Data from Environment Canada.