Advocates say a Montreal mission's failure to open its doors to the homeless during a cold snap earlier this week reflects a lack of of co-ordination between the city and partners.

The city has two warming centres, which are supposed to offer temporary shelter when the windchill drops below -27 at night. 

Overnight Monday, it dropped to -28 with the wind chill at Trudeau airport.

But the city says one of those centres, the St. Michael's Mission, failed to open its doors because they had "misinterpreted the forecast."

St. Michael's has promised it won't happen again.

Alexandre Paradis, an outreach worker with SOS Itinérance, said the city needs to do more to ensure homeless people have a safe place to go when the temperature drops.

Paradis said it's hard for people on the streets to know which locations are open and when.

He has launched an online petition calling for centres to open their doors once the wind chill hits -15.