The following is the EC summary of weather events over the stormy past weekend of Friday, July 19, 2013 and Saturday, July 20, 2013. EWR adds some of our graphics and info from our own monitoring activities below the summary.

Environment Canada Summary:

Updated weather summary for all of Southern Ontario and the
National Capital Region issued by Environment Canada
At 10:46 AM EDT Monday 22 July 2013.

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==weather event discussion==

A hot and humid air mass ahead of a cold front provided the perfect
combination to set off severe thunderstorm activity across Central
and Southern Ontario Friday. The severe weather became extensive
during the afternoon and evening hours resulting in the biggest
severe weather outbreak of the season. An exceptionally large area
was affected, from Windsor to Ottawa and from Lake Erie to North Bay.

Friday morning, thunderstorms gave severe wind damage to callander
(near North Bay) resulting in the declaration of a state of emergency
for the town.

Severe thunderstorms continued to develop eastward and southward. In
the early afternoon, storms produced a swath of damage from Pembroke
to Petawawa where cars were flipped over, roofs blown down, trees
uprooted, street lights snapped, and trailers overturned. By late
afternoon, wind damage was reported in dozens of communities in a
broad swath from Lake Huron and Georgian Bay through to Eastern
Ontario.

The severe storms developed southward during the evening hours,
causing wind damage in the Golden Horseshoe and in Southwestern
Ontario. Flooding and downed trees were reported in Niagara Falls
with rainfall estimated at 75 to 100 mm. 150 mm was reported to have
fallen at Rondeau bay.

2 minor injuries were reported in Chatham late Friday evening when a tree fell on a car with the people in it.

Hundreds of thousands of residents were left without power following the storms. As of this morning, approximately 17,000 homes remained
without power.

Environment Canada storm damage teams have investigated damage in
Barrie, Orillia, Gravenhurst, Hamilton, Petawawa, callander and
Dufferin County. The most severe damage was found near honeywood, in
duffern county, where estimated winds of 150 km/hr destroyed a cattle
barn and threw the roof 300 metres. This damage rates ef1 on the
enhanced Fujita scale. Evidence thus far indicates that the storm
damage in Ontario was caused by straight-line, downburst winds.

Below is a list of the most significant damage reports that
Environment Canada has received as of 7:00 PM Sunday.

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Time(lcl) location event description

11:20 AM Gravenhurst 2.5 cm hail

12:40 PM Petawawa and roof damage, trailers flipped,
Pembrooke power outages

12:55 PM Petawawa plaza front facet off, windows blown out,
Roof caved in

1:55 PM Gravenhurst large trees down, power lines down

2:30 PM Coldwater trees down and snapped, power outages

2:45 PM Gravenhurst cars overturned

2:50 PM Orillia trees down, power lines down, street
Lights snapped

2:55 PM lake dalrymple power lines and trees down

3:00 PM W of Ottawa roof damage, crop damage, trees down

3:00 PM’s of Gull Lake 150 trees down on South Morris island

3:15 PM Barrie funnel cloud, trees down – caused
Damage to homes

3:20 PM se of tree damage
Bracebridge

3:20 PM Bobcaygeon trees uprooted

3:30 PM Kanata large hail

4:00 PM N of Arthur trees down

4:35 PM Barrie building damage, trees snapped,
Power outages

4:50 PM Listowel wind gust of 92 km/h

5:10 PM Ottawa trees down (primarily in west end)

5:10 PM Borden wind gust of 96 km/h

5:10 PM mulmar barn roof thrown 300 metres, barn
Destoyed near honeywood, ef1 damage,
Winds estimated at 150 km/hr.

5:15 PM Napanee trees down, gas leaks, power outages

5:30 PM Innisfil funnel cloud, limbs down

5:30 PM Waterloo arpt wind gust of 119 km/h, trees down

5:35 PM sw of Bradford funnel cloud

5:40 PM Guelph dozens of trees snapped or uprooted,
Hundreds of branches down, damage to
Homes from fallen trees or limbs

5:45 PM Casselman 53 mm rain

5:50 PM Kitchener trees down – caused damage to homes,
-Waterloo power outages, damage to bus shelter

5:50 PM Stratford trees down

5:55 PM Port Carling mature trees down, trees snapped
Port Severn

5:55 PM Gravenhurst large trees down, power lines down

6:00 PM Toronto Pearson wind gust of 104 km/h

6:00 PM paris tree damage, wooden balcony torn off
House, cinderblock warehouse collapse

6:10 PM Toronto trees down, including a
Historic century old tree, power
Lines down

6:30 PM Hamilton trees down

6:45 PM Stoney Creek trees down, trees snapped

7:05 PM Hamilton arpt wind gust of 104 km/h

7:10 PM St Catharines trees down, 75-85 mm of rain,
Flooding

7:3o PM Chatham trees down, power lines down,

7:45 PM Grimsby trees down, power outages, 65 mm of
Rain

7:45 PM Waterdown trees down

8:20 PM Chatham-Kent trees down, power outages

8:30 PM Ancaster trees and power lines down, small
Hail

8:45 PM norwich wind gust of 90 km/h, trees down

9:00 PM mulmur barn damage, crop damage, roof
Damage, power outages

9:10 PM Hamilton arpt wind gust of 106 km/h

9:20 PM Mount Hope trees down, trampoline blown onto
Roof, crop damage

10:00 PM Port Colborne wind gust of 98 km/h

11:00 PM Port Colborne wind gust of 93 km/h, power outages

02:00 AM (sat) Waterloo arpt wind gust of 91 km/h

Reports with exact time unknown:

St George trees and hydro lines down
Essex County trees down
Simcoe County trees down
Rondeau bay 150 mm rain
Chatham minor injuries to two passengers of
A car
Wiarton large tree uprooted
Blenheim trees down, flooded basements, power
Outages
Niagara Falls 75-100 mm rain, flash flooding
Beamsville/ 75-85 mm rain, flash flooding
Vineland

This weather summary contains preliminary information and may not
constitute an official or final report.
____________________

Observations from EWR:

EWR’s rain gauge measured 35mm of rain by the completion of the frontal passage Saturday morning. In the radar animation below, covering the time from 7:28 pm Friday to 9:01 am Saturday morning, two storm systems collided over the Niagara Escarpment at Grimsby at approximately 9:10PM Friday evening (early part of the animation). The westernmost system advanced eastward along the north shore of Lake Erie from the St. Thomas area, and colliding with the system moving southerly across the GH-GTA from the Kitchener-Waterloo area. The Lake Erie system was strongly electified, and the light show was impressive. The gust front from that system was strong with torrential rain in wind as it passed over Dundas, Ancaster and Hamilton. The bulk of the rain we measured at EWR came from that gust front.

20130720 Click image to start animation if it doesn’t start on its own.

[click on any of the following images to see them full size]

2013-0719-srv1-619

This Storm Relative Velocity* image, taken at 6:20pm on Friday, shows two areas of rotational development along the gust front of the storm line that had just arrived from the Kit-Wat area. The inverted pink triangle is a “TVS signature” sent out by the KBUF radar system, indicating conditions for tornadic rotation exist. Immediately to the right of the TVS signature is a very tight “couplet” – bright red and green, indicating that rotational winds exist. The beam centre at this distance from the Buffalo station is about 4300 feet, so it is unknown if this rotation yielded a waterspout or not (its over Lake Ontario at this point).

South of Cobourg, another area of suspected rotational development – quite a large area, suggesting the storm cell is developing a rotating core. The bright green is suggestive of a strong in-flow jet.

When this storm passed over Dundas, there was a strong “fresh earth” smell to the storm leading edge, and a bit of “greenness” to the advancing shelf. Both are suggestive that there had been tornadic activity in the cell in its travels, or at least very strong updraft over open land.

* Storm Relative Velocity – a radar measure of the direction and intensity of winds in a storm, relative to the wind velocity over ground of the storm. Visualizes the wind within a storm, as opposed to the wind we feel over ground. Green – winds flowing toward the radar station, red, flowing away. To be tornadic the couplet must straddle a radial – a line drawn from the radar site to a couplet.

2013-0719-srv2619-2

This image is a zoom-in of the previous one, to get a better look at the couplet. Key elements are the tight and intense colour change. This is indicative of very tight rotation, consistent with a small but well defined funnel, tornado or waterspout.

2013-0719-srv3637--1

A combined Storm Relative Velocity (right) and Base Reflectivity view of the previous area, approximately 20 minutes later. The storm line has moved further across the lake. The previous couplet has dissipated, and a new TVS has come up, although there isn’t any overt indication in the SRV pattern to indicate a cell. These views only represent one angle sweep – the lowest tilt – there may have been more evidence in higher tilts.

The Coboug pattern is better defined and is most likely a strong inflow jet. This is borne out by the shape of the cell in the Base Reflectivity scan. This is a tornadic supercell in the making, but it didn’t mature much beyond this phase.

Of interest, is the well defined “gust front” shelf or roll cloud formed ahead of the storm over Niagara. Notice the thin cloud line in the base reflectivity scan, and the thin green and red line in the SRV scan, stretching from Youngstown in a gentle arc eastward out of the frame, just ahead of the main cloud mass.

2013-0719-srv5638-1

This image is the same as the previous scan, just one radar cycle later. The TVS icon has dropped, but the Cobourg cell is maintaining its integrity.