Mild start to the Mother’s Day weekend with heavy rain likely Monday

Some rain expected on Monday. Jodi Hughes has a look at the five-day forecast from the Sky Watch Weather Centre.

A dominant ridge of high pressure that has been serving as the main weather-maker for most of southern Alberta over the past few days is starting to flatten and track to the east.

Behind it lies an intense low pressure system that, as of Friday morning, was still in the north Pacific basin.

That low is expected to elongate and strengthen over the next couple of days as it slowly moves onto the coast.

Along the eastern edge of that system intense rain will form, potentially producing heavy accumulations in southern Alberta and B.C.

Daytime highs for the start of the weekend will remail above seasonal for most of Alberta, with a range of 21 C to 25 C in Calgary from Friday through Sunday.

As is typical of upper pattern weather changes this time of year, there will likely be a rapid deterioration in temperatures and conditions once that low starts to affect southern Alberta.

In Calgary, strong wind and a quick drop in temperature late Sunday will be the first indications of this frontal system taking over.

The combination of the topographical barrier of the Rockies, the lag in the upper pattern movement, and the counter-clockwise rotation around that low will create an upsloping effect that makes it challenging to predict exact precipitation totals, however there are early indications that and by Monday rainfall totals of 15 or 20 millimetres are possible in and around Calgary.

A gradual recovery is expected to start on Tuesday with a return to seasonal temperatures by the middle of the week.