Hamilton Mountain, ON F1 Tornado of August 4, 1999

City of Hamilton

This tornado touched down at 1:10 pm and had a path that was 4 km long and 50m wide. Trees were snapped and uprooted and five houses damaged, one of which had most of its roof torn off. Witnesses observed watching a circular cloud of debris swirling through the street.

This was one of three tornadoes to touch down in Southern Ontario on August 4; the others were an F1 at Clear Creek and a damaging F2 that hit Flamborough and Burlington.

Figure 1 depicts the surface observations at 2:00 pm, which shows a low pressure system exiting Ontario with a cold front across Lake Erie. The low pressure would have brought southwesterly winds across Toronto and Hamilton, which could have activated the lake-breezes across Lake Ontario. Figure 1 depicts an ongoing thunderstorm over Hamilton (marked as an “R”), which is responsible for this F1 tornado.

Figure 1. Surface analysis at 18Z on August 4, 1999 showing mean sea-level pressure (MSLP) contours, surface observations, fronts and pressure centres (WPC, 2017)

According to Environment and Climate Change Canada (2018), an F1 tornado touched down at 1:10 pm EDT near Hamilton Mountain, ON. The tornado travelled for 4 km with a maximum width of 50 metres. The tornado caused no fatalities or injuries, but caused $100 thousand dollars in property damage.


NWS Weather Prediction Center Surface Analysis Archive. (2017). Surface analysis 18Z Wed Aug 4 1999. Retrieved from: https://www.wpc.ncep.noaa.gov/archives/web_pages/sfc/sfc_archive.php

Environment and Climate Change Canada Data. (2018). Canadian National Tornado Database: Verified Events (1980-2009) – Public. Retrieved from: http://donnees.ec.gc.ca/data/weather/products/canadian-national-tornado-database-verified-events-1980-2009-public/