***I recommend using earphones/headphones (bass amplified) to hear the more natural sound of the thunder***
A video compilation highlighting the severe thunderstorms and powerful straight-line winds that affected the West Island of Montreal. Very strong shearing fields (including 0-6 km shear), and robust lift associated with a pre-frontal trough led to scattered to numerous multi-cell thunderstorms.Despite meager solar heating and weak mid-level lapse rates (5.5-6 C/km), SBCAPE/MUCAPE approached 2000 J/kg (locally up to 2500 J/kg). Surface moisture was also very rich, with a maximum dewpoint of 22 C. Low-level lapse rates of 6.5 to even 7 C/km managed to unfold, despite weak heating. Gusty surface and near-surface winds also strengthened moisture convergence and moisture transport into thunderstorms.
A squall line eventually formed, extending mostly into upstate New York. At the Northern end of this line, a bowing segment developed (as shown in the provided radar imagery). A bowing segment is represented by a family of thunderstorms exhibiting distinct curvature, in the form of an archer’s bow. This is caused by strong mid- to upper-level winds (as mentioned, 0-6 km bulk shear was magnified), pushing the thunderstorms rapidly forward and subsequently causing the bow shape. This cluster formed quickly and rushed through the island, suggesting an amplified damaging wind threat, especially at the center of the bow (due to the greatest forward motion located there). Indeed, this bowing cluster (which included a powerful wet microburst), generated incredible force with its wind and rain.
As mentioned, this thunderstorm cluster included a microburst. A microburst is a localized but intense downdraft (downward acceleration of cooled air) that is accompanied by a strong to severe thunderstorm, though it has also occurred independently of a thunderstorm. Because the moisture/humidity level was so rich, this was a wet microburst (a dry microburst forms in a drier environment and is, thus, more driven by significant evaporative cooling of rain droplets). In the case of a wet microburst, combined with some evaporative cooling, the intense water loading within the thunderstorm causes an enhancement in the downward motion of air towards the surface through the thunderstorm's downdraft.
At its height, more than 95,000 customers (potentially in excess of 115,000) were without electricity across Southern Quebec, and massive (tree) damage was reported in NDG (with many reports describing the situation as a war zone). Tree damage was typically observed during/following the sudden forceful gusts of wind. My dwelling sustained a combined outage of 12 hours, 25 minutes and 57 seconds (some of which is shown during the very end of the video). Rainfall was ferocious, and winds induced some property damage to some nearby homes, but principally trees (mostly small twigs, branches and leaves scattered). The highest gust was measured at 113 km/h, at St-Hubert airport (82 km/h at Trudeau airport). Signs were also flipped over, and traffic lights were temporarily out of order. A tornado threat was also prominent due to magnified veering wind fields in the boundary layer, and a touchdown (EF-1 intensity, with 175-180 km/h maximum winds) occurred around Lachute with the initial cluster of thunderstorms that had formed in advance of the eventual squall line.
Ideal start times for loud thunder:
22:22
23:20
24.28
25:50
Closer thunderstorm entry begins at 14:37. Aftermath begins at 33:57.
Footage was taken in SW Pierrefonds, Kirkland and Pointe-Claire, located in Montreal’s West Island.
~Trav.~
Негізгі бет Severe thunderstorm and microburst in Montreal - August 22nd, 2017
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