With temperatures across much of southern Alberta and Saskatchewan forecast to soar into the mid-30s this week, Environment Canada has issued a “yellow” heat warning for a large area stretching from just east of Edmonton to Estevan in southeastern Saskatchewan.

The national weather agency says the warning will be in effect for the next four days, with temperatures in many areas, such as Medicine Hat  Regina and Saskatoon, soaring into the mid-30s.

While Calgary, Edmonton, Red Deer and Lethbridge are just outside the area covered by the heat warning, the temperature in those Alberta cities is forecast to hit the high 20s or low 30s.

“We could also see a chance of thunderstorm later today (Tuesday) as well,” said Global Calgary weather specialist Leslie Horton.

The extreme heat means nighttime temperatures in many areas are also forecast to be in the 20 C range — about the same as normal daytime highs.

Normal nighttime temperatures are in the high single digits.

Environment Canada is advising people living or visiting the areas covered by the heat warning to limit their outdoor activities to the cooler hours of the day or if they must be outside, to watch for symptoms of heat stroke or heat exhaustion, drink plenty of water and pay special attention to infants, children, seniors and people with pre-existing medical conditions who may be more susceptible to the extreme temperatures.

While temperatures in the 30s are expected to continue through the weekend in Saskatchewan, cooler temperatures are in the forecast for southern Alberta with showers or periods of rain expected on Saturday and a high of 19 C in Calgary and 22 C in Edmonton.