Southern Ontario Tornado Outbreak of 2005 - Meteorological Events

Meteorological Events

On the early morning of August 19, a low pressure area was sitting over Northern Michigan with a cold front southwestward. This same systems had been giving an outbreak of tornadoes over Wisconsin the day before. As shown in the map to the left, there was up to 50 mm (2.0 in) of precipitable water in the air mass in the warm sector invading Southern Ontario with a strong southwesterly low level jet parallel to the cold front and the presence of an upper jet-stream. All of these were very favorable from the development of severe thunderstorms. Furthermore, the wind shear in the lower troposphere was creating a large helicity value conducive to a tornado potential.

With the advancing cold front, two lines of thunderstorms developed. The first one was near Stratford, Ontario (20 km (12 mi) west of Kitchener), and spread as far north as Georgian Bay near Collingwood, Ontario while the second one was following behind near the shores of Lake Huron. They tracked eastward and reached as far as Oshawa during the afternoon. Dozens of storm cells populated the line, two of them developing into tornadic supercells. At their worst, the tornadoes reached the F2 level, with gusts between 180 to 250 km/h (110 to 160 mph). Severe thunderstorm warnings were sent, mentioning the possibility of tornadoes in view of the radar output and the potential analysis.

The main storm, later dubbed the Toronto Supercell, spawned a first tornado tracking through Milverton (43°34′N 80°56′W / 43.567°N 80.933°W / 43.567; -80.933 (Milverton)) to Conestogo Lake (43°41′09″N 80°43′49″W / 43.68579°N 80.730293°W / 43.68579; -80.730293 (Conestoga Lake)) (west of Elmira) from 12:40 to 1:20 pm local time. A second twister moved from Salem (43°41′36″N 80°26′49″W / 43.69333°N 80.44694°W / 43.69333; -80.44694 (Salem)) to Lake Belwood (43°46′5″N 80°20′8″W / 43.76806°N 80.33556°W / 43.76806; -80.33556 (Lake Belwood)) (north of Guelph), passing just to the north of Fergus 10 minutes later. When the storm came close to the Greater Toronto Area, a tornado warning was issued, but the storm changed its characteristics. It produced winds of well over 100 km/h (62 mph), golf ball sized hail, but mostly heavy rain flooding many parts of the city between 2 and 4 pm.

Finally, another severe storm passing Southeast of Stratford, in the Tavistock area (43°12′45″N 80°50′51″W / 43.212513°N 80.847462°W / 43.212513; -80.847462), gave an F1 tornado with winds between 120 to 150 kilometres per hour (75 to 93 mph) by 3:20 pm.