Weather warning: Heatwave will make it feel like 45 C in southern Ontario

A multi-day heat event is expected to bring dangerously hot and humid conditions to parts of southern Ontario beginning Monday.

Environment Canada says the heat event will begin Monday and continue until either Wednesday evening or Thursday evening, depending on the region.

Tuesday is expected to be the hottest day, with daytime highs reaching near 36 C in some areas and humidex values climbing as high as 45.

Mississauga, Brampton, Halton, Hamilton, Toronto and Durham Region are among the areas under a heat warning, with daytime highs ranging from 30 to 36 C. Overnight temperatures are expected to remain between 20 and 23 C, providing little relief from the heat.

The weather agency also warns that the hot and humid conditions could lead to deteriorating air quality, with the Air Quality Health Index approaching the high-risk category in some areas.

Environment Canada says extreme heat can affect everyone’s health, particularly older adults, infants, young children, pregnant individuals, people with chronic illnesses and those who work or exercise outdoors. Residents are encouraged to check in regularly on older adults, people living alone and others who may be at greater risk of heat-related illness.

Individuals should watch for early signs of heat exhaustion, including headache, nausea, dizziness, thirst, dark urine and intense fatigue. Anyone experiencing these symptoms should stop their activity, move to a cooler place and drink water.

Heat stroke is a medical emergency. Symptoms may include red and hot skin, dizziness, nausea, confusion or changes in consciousness.

Residents are urged to call 911 immediately if someone shows signs of heat stroke and try to cool the person by moving them to a cooler location, removing excess clothing and applying cold water or ice packs while waiting for emergency responders.

Environment Canada also recommends drinking water regularly before feeling thirsty, limiting direct exposure to the sun, scheduling outdoor activities during the coolest parts of the day, wearing lightweight, loose-fitting and light-coloured clothing and never leaving children, pets or anyone else inside a parked vehicle.

Residents without access to air conditioning are encouraged to seek cooler public spaces such as libraries, community centres, cooling centres or shaded parks. If wildfire smoke is present during the heat event, officials advise prioritizing staying cool while following guidance from local public health authorities.

• Agawa
• Lake Superior Park
• Apsley
• Woodview
• Northern Peterborough County
• Atikokan
• Shebandowan
• Quetico Park
• Bancroft
• Hastings Highlands
• Denbigh
  Barrie
• Collingwood
• Hillsdale
• Barry’s Bay
• Killaloe
• Bayfield Inlet
• Dunchurch
• Belleville
• Quinte West
• Eastern Northumberland County
• Big Trout Lake
• Kasabonika
• Blind River
• Thessalon
• Bracebridge
• Gravenhurst
• Brantford
• County of Brant
• Brockville
• Prescott
• Bruce Peninsula
• Sauble Beach
• Tobermory
• Caledon
• Chatham-Kent
• Rondeau Park
• Cobourg
• Colborne
• Western Northumberland County
• Cornwall
• Lancaster
• Deep River
• Whitney
• Eastern Algonquin Park
• Dunnville
• Caledonia
• Haldimand
• Elliot Lake
• Ranger Lake
• Espanola
• Killarney
• Fenelon Falls
• Balsam Lake Park
• Northern Kawartha Lakes
• Fort Albany
• Gananoque
• Mallorytown
• Goderich
• Bluewater
• Southern Huron County
• Greater Sudbury and vicinity
• Guelph
• Erin
• Southern Wellington County
• Haliburton
• Minden
• Southern Haliburton County
• Hanover
• Dundalk
• Southern Grey County
• Huntsville
• Baysville
• Innisfil
• New Tecumseth
• Angus
• Kaladar
• Bannockburn
• Bon Echo Park
• Kingston
• Odessa
• Frontenac Islands
• Kitchener
• Cambridge
• Region of Waterloo
• Lindsay
• Southern Kawartha Lakes
• Listowel
• Milverton
• Northern Perth County
• London
• Parkhill
• Eastern Middlesex County
• Manitoulin Island
• Maxville
• Alexandria
• Merrickville-Wolford
• Kemptville
• Midland
• Coldwater
• Orr Lake
• Moosonee
• Morrisburg
• Long Sault
• Mount Forest
• Arthur
• Northern Wellington County
• Napanee
• Consecon
• Newmarket
• Georgina
• Northern York Region
• Niagara Falls
• Welland
• Southern Niagara Region
• North Bay
• Powassan
• Mattawa
• Orangeville
• Grand Valley
• Southern Dufferin County
• Orillia
• Lagoon City
• Washago
• Ottawa North
• Kanata
• Orléans
• Ottawa South
• Richmond
• Metcalfe
• Owen Sound
• Blue Mountains
• Northern Grey County
• Oxtongue Lake
• Fort Irwin
• Northern Haliburton County
• Petawawa
• Pembroke
• Cobden
• Peterborough City
• Lakefield
• Southern Peterborough County
• Picton
• Sandbanks Park
• Plevna
• Sharbot Lake
• Western Lanark County
• Port Carling
• Port Severn
• Prescott and Russell
• Renfrew
• Arnprior
• Calabogie
• Rodney
• Shedden
• Western Elgin County
• Sachigo Lake
• Bearskin Lake
• Sarnia
• Petrolia
• Western Lambton County
• Saugeen Shores
• Kincardine
• Southern Bruce County
• Sault Ste. Marie
• St. Joseph Island
• Searchmont
• Montreal River Harbour
• Batchawana Bay
• Shelburne
• Mansfield
• Northern Dufferin County
• Simcoe
• Delhi
• Norfolk
• Smiths Falls
• Perth
• Eastern Lanark County
• South River
• Burk’s Falls
• St. Catharines
• Grimsby
• Northern Niagara Region
• St. Thomas
• Aylmer
• Eastern Elgin County
• Stirling
• Tweed
• Madoc
• Stratford
• Mitchell
• Southern Perth County
• Strathroy
• Komoka
• Western Middlesex County
• Summer Beaver
• Wunnummin Lake
• Kingfisher Lake
• Tamworth
• Sydenham
• South Frontenac
• Town of Parry Sound
• Rosseau
• Killbear Park
• Vaughan
• Richmond Hill
• Markham
• Watford
• Pinery Park
• Eastern Lambton County
• West Nipissing
• French River
• Western Algonquin Park
• Lake of Two Rivers
• Westport
• Charleston Lake
• Winchester
• Newington
• Windsor
• Leamington
• Essex County
• Wingham
• Blyth
• Northern Huron County
• Woodstock
• Tillsonburg
• Oxford County

Residents are encouraged to continue monitoring forecasts and alerts issued by Environment Canada.