B.C. has no chill: summer to fall, this system has it all

Parts of B.C. are set for more rain than they've experienced in months.

This is not a drill, Vancouver. A full-fledged fall low-pressure system will sweep across Metro Vancouver and the South Coast on Friday.

With such an abrupt transition, there'll be some issues and dangers with such a quick start to the fall fury.

THE CAUSE

On Thursday, a deepening upper trough was situated in the Gulf of Alaska – quite anomalous for mid-September, residing on the fringes of climatology for September 17th, 2021.

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THE TIMING

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Early Friday morning: The light rainfall builds, and we're comfortably in the 'it's not so bad' stage. It's also snowing on the higher terrain of Whistler at this time – you hear that, skiers?

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Friday afternoon & evening: The core of the atmospheric river pivots across the South Coast, likely triggering some pooling and ponding on roads – with impressive rainfall rates. Check out the hardest-hit regions: they're the usual suspect spots, getting some added totals with the help of the mountains aiding in some forced ascent:

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Rainfall rates will slowly ease overnight before tapering to unsettled showers throughout the day on Saturday.

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The totals are impressive for mid-September; the forecast atmospheric river happens roughly 3-10 times per year, but rarely in September.

The cold trough left in its wake means isolated thunderstorms are now possible on Saturday.

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WATCH BELOW: HEAVY RAIN, STRONG WIND EXPECTED FOR PARTS OF BRITISH COLUMBIA

THE ISSUES

A large portion of the summer remained rain-free, creating significant stress on the trees across the South Coast. During the wicked windstorm of August 2015, 710,000 customers lost power from winds up to 90 km/h. The damage was certainly high for relatively modest wind speeds, but the dry, antecedent conditions were the primary factors.

The forecast wind gusts will remain below 70 km/h will be along the immediate coastline.

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The trees also still have their foliage, which can act as a sail with strong wind gusts.

SATURDAY: THUNDERSTRUCK?

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As a cool trough maneuvers over the South Coast, temperatures cool significantly with height, naturally developing instability and the threat for isolated thunderstorms into Saturday.

Be sure to check back for the latest updates on this early season fall storm in B.C.