Monday's high of 26 C, the coolest high for at least a week

Heat warnings are expected to expand in the west as a prolonged heat event starts to set up across the Prairies.

As of Monday morning, heat warnings had been issued from Environment and Climate Change Canada for portions of southern and northern British Columbia, the Northwest Territories, northern Alberta and areas east of Calgary.

Heat warnings are issued for most of Alberta (excluding the southernmost communities like Medicine Hat, Pincher Creek and Lethbridge) when daytime highs reach a temperature of at least 29 C combined with a daytime low temperature of at least 14 C for at least two consecutive days.

Both daytime high and low temperatures will be above seasonal in Calgary and much of Alberta on Monday. Those temperatures are expected to continue to rise over the next few days.

In Calgary, Monday’s high of 26 C is three degrees above average, but it is also the coolest temperature expected for at least a week.

The synoptic setup will include an Omega block – a northerly riding, clockwise circulating high pressure system that is anchored at the base on either side by counter-clockwise circulating low pressure systems.

These types of blocking patterns can be very difficult to dislodge and can last for a prolonged period of time (a perfect example is the record-shattering Pacific heat dome event from 2021).

Before this pattern is firmly established there is a risk of convective activity on Monday and Tuesday across central and southern Alberta.

The combination of rapid daytime heating along with instability may prompt thunderstorms to fire off the foothills – all the way from Hinton to areas east of Crowsnest Pass.

If those storms do develop, they are expecting to track east fairly quickly, possibly impacting locations along the QEII and Highway 2 corridor including Calgary, Red Deer and Lethbridge.