This ‘Omega block’ will dominate Canada’s weather this week
Is it the middle of summer or the middle of spring? A big block settling over Canada will decide your atmospheric fortunes this week
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It’s been a rough stretch across much of Canada as folks back east deal with historic wildfires and prolific smoke, while the Prairies have dealt with almost a week of nonstop severe thunderstorms and occasional tornadoes.
A pattern change will build over Canada for the first full week of June. This ‘Omega block’ will dominate the country’s weather, locking in the heat for some while others are left to wonder what happened to an early taste of true summertime warmth.
Atmospheric blocks are familiar in recent days
This isn’t the first block we’ve heard about in the past couple of weeks.
Ontario closed out May with a burst of heat more common of the middle of summer than just after Victoria Day.
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That unusual heat came courtesy of a Rex block, which saw a centre of high pressure locked over Ontario for days on end.
A truthful rarity in this day and age, blocking patterns deliver exactly what the name promises. These setups effectively dam the atmosphere over the affected areas, preventing upper-level features from moving along as usual.
Without much progression aloft, conditions can remain constant for many days at a time.
Omega blocks earn their moniker because the resulting upper-level pattern resembles the Greek letter Omega.
This setup features a large ridge of high pressure bookended on either side by centres of low pressure aloft. These blocks can stick around for a while, sometimes shifting slightly west or east for the duration.
Ridges of high pressure foster sinking air that favours above-seasonal temperatures. Folks beneath the troughs, on the other hand, are susceptible to an extended period of cooler and unsettled conditions.
Sustained warmth in the west, cooler and rainy in the east
The Omega block setting up over Canada this week will reinforce the warmth settled over the Prairies in recent days.
It’s so hot and humid in Manitoba, for example, that Winnipeg on Saturday registered a feels-like value of 38 just before a powerful thunderstorm dropped near-record rainfall on the city’s airport.
Heat—often humid at times—will persist on the Prairies for most of the week, with daytime high temperatures routinely climbing into the upper 20s and cracking the 30-degree mark at times. A continued risk for strong to severe thunderstorms will accompany the warmth in many spots.
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This heat will migrate west with the ridge as the week wears on, pushing highs around 30°C into British Columbia’s Lower Mainland by the latter half of the week. Combined with the heat a few weeks ago, it's an unusual feat for the Lower Mainland to reach the 30s twice so early in the year.
Back east, we’ll see falling temperatures and more frequent opportunities for rain to spread over portions of Ontario, Quebec, and the Atlantic provinces through the upcoming week.
The best chance for below-seasonal temperatures and bouts of rain will occur from Ottawa and Montreal east toward the Maritimes and Newfoundland. This will bring relief to areas devastated by recent and ongoing wildfires, including Nova Scotia and interior Quebec.
Southern Ontario will fall right on the edge between the two extremes, likely experiencing near or slightly below-seasonal temperatures this week with mostly fair conditions interspersed with occasional showers for the duration.
