What you need to know about the ‘heat dome’ hovering above B.C., Alberta and territories

Much of British Columbia, northern Alberta and parts of Yukon and the Northwest Territories are experiencing a “heat dome” that is expected to shatter high-temperature records over the next few days.

Temperatures into the 40s Celsius are expected for many parts of B.C. Many communities across the northern half of Alberta could also see temperatures near the 40 C mark by early next week.

Environment Canada meteorologist Bobby Sekhon explains the phenomenon and what to expect in British Columbia.

What is a heat dome?

A heat dome is caused by a strong ridge of high pressure that traps warm air underneath it. Although not a term commonly used by Environment Canada scientists, the heat dome gets its name because the ridge acts like a dome, allowing the sun to crank up the heat below and create a heat wave that lasts at least a few days.

How often does this happen?

Ridges of high pressure create hot spells in B.C. most years but they typically occur in July or August. Another memorable heat wave occurred in July 2009, when there were several heat-related fatalities and some B.C. weather stations smashed temperatures records. On July 30, 2009, the Vancouver airport set its current local record of 34.4 C.

1:40Alberta bracing for ‘historic’ heat wave

How significant is this?

This year’s ridge is much stronger and earlier than usual. The temperatures for this time of year are unprecedented and parts of B.C. are going to set some all-time records, certainly a lot of June records and probably daily maximum records.

Are there particular parts of B.C. you’re keeping an eye on?

The whole province is pretty much under heat warnings, except for parts of the northwest near the Yukon border and some coastal areas like West Vancouver Island up to Haida Gwaii. Some of the hot spots will be places like Lytton, Osoyoos, Port Alberni on Vancouver Island, Chilliwack in the Fraser Valley and Prince George in the north. Environment Canada is forecasting six days of 40-plus temperatures in Kamloops, which has never seen 40 C in June on record.

How does a heat dome go away?

Eventually there will be a ridge breakdown, when the province transitions to cooler weather. Usually that is accompanied with thunderstorms because of built-up energy from the heat.

Once the province gets some destabilization of the atmosphere and some troughs coming in, that usually kick-starts some convection and thunderstorms. If accompanying rain showers are limited, that can create a high risk of wildfires.