Calgary under heat warning; daytime highs of 29 to 33 C until weekend

As expected, heat warnings have been expanded and now include Calgary.

And Lethbridge.

Daytime highs in Calgary are forecast to range from five to eight degrees above seasonal averages with daily lows between four to seven degrees below average.

Environment and Climate Change Canada (ECCC) will issue heat warnings for most of Alberta when daily highs are expected to reach at least 29 C with daily lows of at least 14 C for at least two consecutive days (the threshold from ECCC is slightly higher in the far southern regions of the province, including Medicine Hat, Pincher Creek and Lethbridge).

This hot, dry weather is linked to a ridge of high pressure that begins along the U.S. western coastline and extends into central Alberta.

 

There are some notable differences between this heat event and the one that impacted the western Prairies for much of July.

This system is not anchored, so it will allow for a resumption of meridional flow in the upper levels rather than remain stationary, and this ridge does not extend as far north as the record-setting one from earlier in the month.

Convective activity is expected along the northern edges of the ridge with severe thunderstorms prompting both watches and warnings Wednesday afternoon.

These storms will be fast-moving with the greatest threats being strong wind and large-sized hail.

There is a chance of more thunderstorm activity on Thursday, with some cells potentially firing off of the foothills and tracking east but at this point, the likelihood is quite low for this region.

As this ridge is not expected to remain situated over the west, when it does break down, instability will move in and lower temperatures closer to seasonal values but also bring in some showers and thunderstorms to end the long weekend.

In Calgary, between 12 and 18 millimetres of rain are possible from Sunday through Tuesday, with daytime highs early next week expected to hold in the low 20s.