Tuesday, 5 September 2023

This Day in Weather History - September 5

 September 5, 1996 Bow Echo Downed 19 Vital Hydro Towers

A warm front advancing northward from North Dakota produced some wild weather in southern Manitoba on September 5, 1996. Thunderstorms developed east of Portage la Prairie during the overnight hours and quickly became severe. The storms developed well north of the warm front, which was still in North Dakota. The warm front did not reach Winnipeg until the evening, pushing temperatures and humidity upwards. Despite only reaching 22°C in the afternoon, a sudden switch in wind direction from northeasterly to southerly by 9pm increased temperatures to 26°C. Temperatures fell back below 20°C late in the overnight on the 6th as a cold front moved through. 

The storms during the overnight hours of the 5th were destructive. The storm east of Portage la Prairie quickly became a bow echo, with powerful straight-line winds. It caused extensive damage from Marquette to just east of Grosse Isle. 19 hydro towers near Grosse Isle were toppled. Since this was the main line carrying electricity from northern Manitoba to Winnipeg, this put Manitoba Hydro in a perilous situation, only able to distribute less than half of its regular electricity capacity. Businesses and residents were asked to significantly reduce electricity usage to avoid blackouts. Schools shut off air conditioning and some office buildings turned off lights and computers that were not in use. Residents listened to Manitoba Hydro's pleas, avoiding any rolling blackouts from being necessary. 

In addition, Manitoba Hydro could no longer export electricity and was instead importing. This was costing the corporation about a million dollars per day. 

Environment Canada had done a damage survey and determined that localized wind gusts over 150 km/h were possible where the towers were toppled. One wind gust to 125 km/h was measured just 3 km south of the site at the Dorsey Converter Station. Residents who lived through the storm believed a tornado had struck the region, but Environment Canada's survey determined it was straight-line winds from a microburst/downburst. 

The storms also produced wind gusts to 85 km/h at Winnipeg Airport, from the north-northeast. Winds were quite erratic at Winnipeg Airport from 1 to 4 am, frequently varying between north-northwest and east. Other damages from the storm north of Winnipeg included trees knocked trees, roofs peeled off and toppling grain bins. Downed power lines also caused the closure of Highway 6. Teulon reported about 150 mm of rain from the storms according to Environment Canada. 

Radar image at 1:50am, showing the bow echo over Gross Isle. From Pat McCarthy/Environment Canada

From the Winnipeg Free Press Sep 6, 1996, page 1

From the Winnipeg Free Press Sep 7, 1996, page 7

This post contains information from the Winnipeg Free Press and a publication by Environment Canada's Patrick McCarthy for Manitoba Hydro. Another study was also published about the event in 2011. 

Monday, 4 September 2023

This Day in Weather History - September 4

 September 4, 2015, Heavy Thunderstorms and Extreme Humidity

It was a hot and very humid start to September in 2015. The first three days exceeded 30°C and dewpoint temperatures exceeded 20°C from the 2nd to the 4th. In fact, on the 3rd and 4th, dewpoint values reached a record 23°C, the second highest recorded in September since 1953. Humidex reached 42.0 on the 3rd, the second highest on record in September since 1953. All the humidity culminated in an active thunderstorm day on the 4th. 

It was a very warm and humid night on the 4th. Temperatures hovered near 25°C most of the night, and did not drop to 23°C until mid morning. Thunderstorms developed across southern Manitoba during the overnight hours and dropped large hail. Hail up to toonie-sized fell from Niverville and Ile-des-Chenes to Cooks Creek just east of Winnipeg. Up to dime sized hail was reported in eastern parts of Winnipeg around 2 am. 

It was in the afternoon that the heaviest thunderstorms developed. Locally, over 50 mm fell in the Red River Valley. The Winnipeg area was one of the hardest hit areas with 30 to 50 mm of rain in just under an hour and wind gusts over 80 km/h. The storm struck around 2 pm and it was dark enough for street lights to become illuminated. Significant street flooding occurred, including flooded underpasses. The underpass at Logan and Route 90 was shut down for hours due to flooding. With more rain later in the day, daily totals were between 40 and 60 mm. The airport recorded 41.1 mm for the day, breaking the old daily record of 36.8 mm in 1872. About 31 mm had fallen in an hour, the second highest on record in September. The Forks recorded 38 mm in an hour. The storm resulted in the cancellation of a concert at Assiniboine Park and the baseball game at Shaw Park. Four West Jet flights were diverted to Brandon as a result of the storm, before they could land in Winnipeg. 

From the Winnipeg Free Press Sep 5, 2015, page 4

Cocorahs rainfall amounts Sep 4, 2015. Click to zoom in

Sunday, 3 September 2023

This Day in Weather History - September 3-4

September 3-4, 1912 thunderstorms at night

It was a stunning night of long-lived thunderstorms in 1912. The storms began between 7:30 pm and 9pm in Winnipeg on the 3rd, and continued until about 2 am the 4th. Lightning was vivid and thunder crashed, with torrential downpours lasting intermittently most of the night. The storm played havoc with the electrical system, with the Free Press describing the lighting systems as playing ''hide and seek''. No deal of damage was done to the city however, with the storm's greatest violence apparently missing the city. One horse was struck by lightning and killed near St James. 

About 30-40 mm of rain fell in Winnipeg during the night. Higher amounts occurred in areas outside the city, such as 66 mm in Oakbank. Rainfall amounts via ECCC are as follows:

Oakbank 66.0 mm
Manitou 50 mm (Winnipeg Free Press)
Cartwright 40.1 mm
Winnipeg St John's College 36.6 mm
Portage la Prairie 25.1 mm
Napinka 25 mm (Winnipeg Free Press)
Morden 21.8 mm
Stony Mountain 7.6 mm

From the Winnipeg Free Press Sep 4, 1912, page 1

The storms hit other portions of the province as well, but no major damage was reported. The rains delayed harvesting temporarily. Here are some reports:

Virden - Heavy rain in town last night, and south and east of here. No rain two miles west or north. No damage.
Portage la Prairie - Downpour of rain lasted several hours, completely drenching everything. Harvesting again at a standstill. Storm was accompanied by severe lightning but with no damage from it. 
Gretna - Very heavy rain last night accompanied by hail. Not much damage as most of the grain is cut. South of here in North Dakota, more hail fell and the crop was flattened. 
Snowflake - A fine large barn with the season's hay was burnt last night during one of the worst electrical storms of the season. Rain fell in torrents. 
Carman - The heaviest rainfall of the season last night, the rain continuing through the night. Harvesting cannot be resumed this week as a result. 
Brandon - A fierce thunderstorm broke over the city in the very early hours of the morning and lasted about 2 hours. No damage.
Boissevain - It rained heavily last night for 4 hours with heavy thunder and lightning. Nearly half an inch of rain fell. About 12 farmers suffered loss by hail about 6 miles west of here. Their loss will be about 20-95%. 
Emerson - There was a heavy downpour of rain last night and the ground has been thoroughly soaked. 
Gladstone - There was heavy rain last night. Standing crops laid down badly. 
Melita - Exceptionally heavy rain fell here last night. 
Manitou - Last night's rain was one of the heaviest of the season. Grain was badly beaten down. 
Souris - Rain here last night was quite heavy. 
Dominion City - Heavy fall of rain over the town and immediate vicinity last night. At outside points there was none or very little. 

From the Winnipeg Tribune Sep 4, 1912, page 5

This post contains info from the Winnipeg Tribune, Winnipeg Free Press and ECCC.