News Release

Ontario Weather Review

July 2011

July 2011 will be remembered as one of the hottest Julys on record in Ontario. Record daily temperatures were established during the middle of the month at many locations. The extended periods of heat raised the monthly mean temperatures for many locations a noteworthy 2 to 3 degrees above normal values. All-time monthly records were established through southern and central Ontario.

This past month will also be noted for being the driest in many years for many locations. The only exceptions were the few areas caught in the paths of strong thunderstorms, which brought significant rain in a very short period of time. 

Severe Weather

Heat was the predominant factor in last month’s severe weather. Humidex advisories were posted on numerous days, signalling forecast humidex values of 40 or higher. July 21 was the hottest day in southern Ontario, and on that day the Ontario Storm Prediction Centre in Toronto replaced the Humidex Advisory with a broad-reaching Weather Warning to underscore the severity of the hot weather. 

Southwestern Ontario counties experienced their share of severe weather during the month. On July 2, Windsor experienced an intense thunderstorm which brought 43 millimetres of rain in a few hours. On July 23, two severe thunderstorms moving southeastward across Lambton and Middlesex Counties resulted in tornado warnings being issued. One tornado was confirmed by Environment Canada investigators the next day near Watford in eastern Lambton County. It was rated as an F2 tornado, with maximum winds of 180 to 230 kilometres per hour. This was the third tornado of the season in Ontario. Then on July 28, another series of thunderstorms early in the morning brought 83 millimetres in Harrow and 53 millimetres in Windsor. Due to the number of thunderstorms that rolled through the Windsor area in July, that location ended up with almost 155 millimetres of rain for the month. This is well above their average rainfall of approximately 82 millimetres and was, in fact, their wettest July since 1995. 

A particularly noteworthy event occurred on the evening of July 17, when a squall line moved southeastward down the Ottawa Valley. Wind gusts associated with this line of thunderstorms were measured at 120 kilometres per hour at Petawawa at 6 p.m. and 96 kilometres per hour at the Ottawa airport at 7:30 p.m.  Several people were treated for injuries when the passage of the squall line through downtown Ottawa caused the collapse of the main stage at the Bluesfest Festival.

Another storm which moved through Thunder Bay during the evening of July 20 was responsible for wind gusts of 115 kilometres per hour and removal of part of the roof at the Thunder Bay airport terminal.

More heavy downpours associated with thunderstorms on the morning of July 29 left significant amounts of rain all the way from Wiarton (47.4 millimetres) to Coldwater (74.4 millimetres), Peterborough (59.9 millimetres) and Kingston (71.0 millimetres), causing local flooding.

Finally, discussion of the severe weather in Ontario in July would not be complete without mention of the forest fires which raged across northwestern Ontario during the month. Consecutive months of below-average precipitation in many areas of northern Ontario resulted in the dry conditions which set the stage for the month’s forest fire activity. Smoke from these fires resulted in evacuation of many First Nation communities and was noticed even in areas of central and eastern Ontario.

Temperature and Precipitation Tables

Record high mean temperature readings (in °C), ranked by variation from normal:
Location	Mean Temp	Normal	Difference	Previous Record
Toronto Pearson	24.4	20.8	3.6	24.3 (1999)
Windsor	25.8	22.7	3.1	25.3 (1955)
Elliot Lake	21.4	18.5	2.9	20.3 (2002)
Sarnia	23.6	20.9	2.7	23.2 (1999)
Chapleau	19.5	17.0	2.5	19.1 (1988)
Hamilton	23.3	20.8	2.5	23.2 (1999)
Unusual mean temperature readings (in °C), ranked by variation from normal:
Location	Mean Temp	Normal	Difference	Warmest Since
Toronto City	24.9	22.2	2.7	1921
London	23.2	20.5	2.7	1955
Waterloo	22.3	19.8	2.5	1999
Red Lake	20.4	18.1	2.3	1975
Sudbury	21.3	19.0	2.3	1988
Muskoka	20.8	18.5	2.3	2010
Kapuskasing	19.4	17.2	2.2	2005
Geraldton	19.1	16.9	2.2	2010
Sault Ste. Marie	19.8	17.6	2.2	2010
Pickle Lake	19.8	17.7	2.1	2002
North Bay	20.7	18.6	2.1	2005
Trenton	22.6	20.5	2.1	2010
Wawa	16.9	14.8	2.1	2010
Sioux Lookout	20.6	18.6	2.0	2006
Record low precipitation readings (in mm), ranked by variation from normal:
Location	Precipitation	Normal	Difference	Previous Record
Waterloo	16.5	91.8	-75.3	20.3 (2001)
Sudbury	24.2	76.6	-52.4	25.2 (1963)
Unusual precipitation readings (in mm), ranked by variation from normal:
Location	Precipitation	Normal	Difference	Driest Since
Geraldton	54.0	111.7	-57.7	2006
Dryden	45.4	98.8	-53.4	1978
Red Lake	39.0	90.8	-51.8	1981
Sioux Lookout	35.0	85.3	-50.3	1981
Toronto City	21.9	67.5	-45.6	1983
Toronto Pearson	32.4	74.4	-42.0	2005
Timmins	52.8	91.5	-38.7	2005
North Bay	62.8	100.1	-37.3	2010
Kapuskasing	63.6	100.5	-36.9	2005
Kenora	58.4	95.3	-36.9	2006
London	46.1	82.2	-36.1	2007
Wawa	66.4	101.5	-35.1	2005
Hamilton	51.6	86.5	-34.9	2007
Elliot Lake	47.6	79.3	-31.7	2010
Ottawa	59.6	90.6	-31.0	2010
Unusual precipitation readings (in mm), ranked by variation from normal:
Location	Precipitation	Normal	Difference	Wettest Since
Windsor	154.8	81.8	73.0	1995
Peterborough	138.5	66.7	71.8	2008
Kingston	115.3	59.8	55.5	2004
Trenton	84.2	56.1	28.1	2009
Note: The normal period used is the 1971-2000 Climate Normals.

Media: For more information, please contact:

Jack Saunders
Communications Advisor/Media Relations
Environment Canada - Ontario
416-739-4785