Graphic weather!

The Victoria Standard - - Weather - BILL DANIELSON

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.

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