News Release

Ontario Weather Review

May 2012

May 2012 was warmer than normal for most of the province, with mean temperatures exceeding normal values by as much as 3.7 degrees Celsius.  Southern Ontario even experienced a short-lived hot spell during the last week of the month, with a number of daily maximum temperature records above 30°C set on May 28.

Conditions were drier than normal for most of Ontario: the southwest, east, near north and northeast. Records for low precipitation were set in Sudbury and Chapleau in northeast Ontario, which received 26% and 45%, respectively, of the precipitation expected in the month. On the other hand, northwest Ontario and north of Superior were wetter than normal. Records for high precipitation were eclipsed by impressive differences. Thunder Bay (the Burwood station) received more than three times the precipitation that would be expected in May. Also, Geraldton set a new mark with more than twice its normal precipitation.

Severe Weather

The most significant event of the month was the flooding that occurred in the City of Thunder Bay on May 28. In the days before the flooding occurred, Thunder Bay had received a number of days of noteworthy rainfall, culminating in approximately 40 millimetres falling on May 25. This rainfall left the area fairly soggy and sensitive to any additional rainfall amounts. During the late evening hours of May 27 and the early morning hours of the next day, a low-pressure system moved into North Dakota, with a warm front extending out from the low up to south of Thunder Bay. The air mass over Thunder Bay was very moist and unstable, and the warm front acted as a focus of thunderstorm development during this time. A series of heavy thunderstorms formed and re-formed over the Thunder Bay area between roughly midnight and 4 a.m. on May 28. Environment Canada rain gauges recorded between 91 and 97 millimetres of rain with these storms, and a Lakehead Region Conservation Authority rain gauge reported an amount exceeding 105 millimetres. The flooding which resulted from this rain caused a number of road washouts, significant basement flooding and the flooding of a sewage treatment plant.

Elsewhere in the province, the other noteworthy events during the month were the first two tornadoes of the season. The first tornado occurred in the small community of Orono, to the east of Oshawa, during the late afternoon of May 22. The tornado, which was relatively weak and short-lived, passed over a farmer’s field, leaving no significant damage in its wake. With no noteworthy damage reported, this tornado was rated as a Fujita Scale Zero event, with peak winds to 100 kilometres an hour. This is the lowest rating on the Fujita Scale which goes from F Zero (weakest) to F5 (strongest).

The second tornado of the season occurred a week later on May 29 in the small community of Bourget, located about 40 kilometres east of Ottawa. This event was also relatively weak and short-lived, with a path of damage approximately three kilometres long and some 50 metres wide. Some trees were uprooted and minor roof damage was reported. This event was also rated as a Fujita Scale Zero tornado. Other parts of Eastern Ontario also experienced some wind damage from other thunderstorms in the area on this day, including the Alexandria area (where an old barn was levelled) and the Merrickville and Kemptville areas (where some tree damage was noted).

Ontario normally averages 13 tornadoes each year in a season that runs from late April until early October.

Unusual mean temperature readings (in °C), ranked by variation from normal:

Location	Mean Temp	Normal	Difference	Warmest since
Toronto Pearson	16.6	12.9	3.7	1998
Windsor	18.1	14.9	3.2	1998
London	16.1	13.0	3.1	1998
Hamilton	15.9	12.9	3.0	1998
Wawa	11.2	8.2	3.0	2010
Toronto City	17.1	14.2	2.9	2010
Sarnia	15.5	12.7	2.8	1998
Chapleau	12.2	9.4	2.8	2010
North Bay	14.0	11.2	2.8	2010
Kitchener-Waterloo	15.2	12.5	2.7	1998
Ottawa CDA	16.3	13.6	2.7	1999
Sudbury	13.7	11.3	2.4	2010
Wiarton	13.3	10.9	2.4	2010
Earlton	12.8	10.5	2.3	2010
Petawawa	13.9	11.9	2.0	2010

Record high precipitation readings (in mm), ranked by variation from normal:

Location	Precipitation	Normal	Difference	Previous record
Thunder Bay	209.0	66.5	142.5	174.2 (1971)
Geraldton	147.0	69.1	77.9	132.3 (2007)

Record low precipitation readings (in mm), ranked by variation from normal:

Location	Precipitation	Normal	Difference	Previous record
Sudbury	20.6	77.5	-56.9	22.1 (1977)
Chapleau	32.8	72.7	-39.9	34.7 (1998)

Unusual precipitation readings (in mm), ranked by variation from normal:

Location	Precipitation	Normal	Difference	Driest since
North Bay	23.8	87.6	-63.8	1982
London	21.1	82.9	-61.8	1954
Muskoka	33.6	91.1	-57.5	2005
Hamilton	24.0	75.6	-51.6	1965
Wiarton	24.2	75.3	-51.1	2005
Petawawa	26.0	68.5	-42.5	1977
Earlton	27.2	67.0	-39.8	2011
Sarnia	35.5	69.9	-34.4	1998
Toronto City	41.8	73.3	-31.5	2010
Kingston	44.7	74.8	-30.1	2010
Toronto Pearson	44.4	72.5	-28.1	2005

 

Location	Precipitation	Normal	Difference	Wettest since
Sioux Lookout	134.5	64.4	70.1	2007
Pickle Lake	114.2	60.3	53.9	1959
Red Lake	102.8	54.6	48.2	2011
Dryden	108.2	67.2	41.0	2010
Kenora	104.8	64.3	40.5	2010

Media: For more information, please contact:

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

(Également offert en français)