During these warmer months, the Mustard Seed’s southeast Calgary shelter has seen about 100 people staying at the shelter overnight, with another 50 at its overflow site.

"Whenever we have sudden change in temperature or a sudden decrease in the temperature, we do see a surge of people coming to the shelters. They might be staying outside or wherever they're at and also it makes sense for them to come inside," said shelter supervisor Andrew Millar.

Sunday, Environment Canada issued a special weather statement, calling for an "abrupt transition to fall" this Labour Day long weekend for southern Alberta. It's because daytime highs are well below seasonal and a total of five to 30 mm of rain is possible by Monday evening.

"This is going to be a bit of a warning for us about what’s to come," said Millar. "There’s a lot fewer people in the shelter system and we’re not sure where they are. We know that with worse weather, they’re going to come in and start staying at the shelter and they’re going to start straining the system, so we’ve been concerned about that. We’ve been collaborating with other shelters, discussing with other shelters about how to be prepared for that."

Under normal circumstances, the Mustard Seed’s southeast shelter has capacity of 370, with the pandemic and physical distancing requirements, capacity is down to 238.

Millar said he anticipates another 30 to 40 people will stay at the shelter overnight for the next few nights.

"We can manage those numbers for sure."

Millar said the shelter has been aggressive about screening to prevent the spread of COVID-19, saying an isolation centre at a different building has been used.

"We’ll put them into isolation, where they can stay safety and get tested and cleared before they come back and re-join us in the shelter, to prevent the infection from getting inside the building."

FROST IN THE FORECAST

According to Environment Canada, frost is likely across most of Alberta on Monday and Tuesday mornings, especially in southern and central areas.

Forecasters say a low-pressure system tracking along the eastern prairies will bring showers, gusty wind and cooler daytime highs in the 10-15 degree Celsius range.

"A cold air mass will slide south in the wake of the system and entrench itself over Alberta by Monday morning, with overnight low temperatures falling below freezing. Currently, snowfall is expected to remain in and near the mountain parks, however there is a chance of seeing mixed precipitation in areas along lower elevations of the foothills, including Calgary," Environment Canada's statement reads.

There was also some snow in areas of the city Saturday night, but the agency says it won't stay for long.

"Snowfall totals at this time are very uncertain as the warm ground and the confidence in the timing of the changeover to snow is not high. Daytime heating on Monday will also limit the snowfall accumulation potential."