News Release

Ontario Weather Review

September 2011

For the most part, Ontarians experienced beautiful summer weather in September, with a drastic transition into fall.

Most of Ontario reported warmer-than-normal mean temperatures this month. About mid-month, a cold low stalled over Lake Michigan causing sunny and warm conditions (to the mid-twenties) in south central and eastern Ontario. Meanwhile, south western Ontario experienced milder and more variable weather conditions.

Total precipitation records remained intact this month; however, south western Ontario received above-normal precipitation amounts. Windsor received 228 millimetres of rain which is the second highest precipitation amount for September since observations began in 1940. The wettest September for Windsor remains the one in 1981 when 246.1 millimetres of rain fell. Overall, southern Ontario, received near-normal precipitation amounts, while northern Ontario received below-normal to normal precipitation amounts.

As a not-so-gentle reminder that colder weather is on the way, snow fell in a few northern locations around mid-September. Chapleau, Geraldton, Kenora, Pickle Lake, Red Lake, Sault Ste Marie, Sioux Lookout and Wawa received snowfall amounts that ranged from trace to 0.8 centimetres.

Severe Weather

This summer’s severe weather arrived late in the season, reminding us that the beginning of the school year and the approaching autumn do not always pair with quiet weather. Ontario’s summer severe weather season normally extends from mid-April to early October.

Severe storms arrived on September 2, causing turmoil in north western Ontario. A few areas saw hail, including Murillo, just west of Thunder Bay, which reported seeing hail as large as a baseball. An Environment Canada investigator assessed structural and tree damage in the same area, and concluded that the cause was downburst wind from a severe storm, with peak winds in the order of 120 to 170 kilometres per hour. 

On the afternoon of September 3, Ontario’s 14^th tornado occurred near Grimsby, in the Niagara Region. It was rated as a Fujita scale zero tornado with peak winds to 110 kilometres per hour. The tornado was spun from one of the strong-to-severe thunderstorms that were triggered by a cold front over southern Ontario on that afternoon.

The storms triggered by the cold front also caused roof damage, brought trees and power lines down and spread up to marble-sized hail in parts of south western Ontario. Wind gusts between 80 to 100 kilometres per hour were reported at several observation stations from Windsor to Pearson Airport in Toronto. An Environment Canada investigator confirmed straight line wind damage in the Kitchener-Waterloo area, including the St. Jacobs Farmers’ Market, where it was reported that five people were injured.

Temperature and Precipitation Tables

Unusual mean temperature readings (in °C), ranked by variation from normal:
Location	Mean Temp	Normal	Difference	Warmest since
Petawawa	16.1	12.5	3.6	2002
Ottawa	17.3	14.3	3.0	2002
Pickle Lake	12.0	9.2	2.8	2009
North Bay	14.7	12.2	2.5	2007
Toronto Pearson	17.7	15.3	2.4	2007
Moosonee	11.7	9.4	2.3	2009
Red Lake	12.6	10.3	2.3	2009
Wawa	12.8	10.7	2.1	2007
Sioux Lookout	13.0	10.9	2.1	2009
Timmins	12.4	10.3	2.1	2009
Trenton	16.8	14.8	2.0	2005
Muskoka	14.9	12.9	2.0	2007
Unusual precipitation readings (in mm), ranked by variation from normal:
Location	Precipitation	Normal	Difference	Driest since
Thunder Bay	33.0	88.0	-55.0	2009
Sioux Lookout	53.4	95.3	-41.9	2009
Sudbury	63.3	101.3	-38.0	2007
Dryden	53.0	90.4	-37.4	2010
North Bay	79.4	113.5	-34.1	2009
Wawa	86.8	120.8	-34.0	2009
Location	Precipitation	Normal	Difference	Wettest since
Windsor	228.0	96.2	131.8	1981
Wiarton	165.4	104.3	61.1	2010
London	136.5	97.7	38.8	2006
Hamilton	116.0	82.1	33.9	2006
Sault Ste Marie	128.3	96.5	31.8	2010

Note: The normal period used is the 1971-2000 Climate Normals

Media: For more information, please contact:

Laurie Thibeault
Communications Advisor
Environment Canada – Ontario
905-336-4711