Metro Transit's cold weather protocol is in effect this weekend to protect passengers and others in the dangerously frigid weather.

Transit centers stayed open all night Saturday and are expected to do so again Sunday night, while the 5 and 19 buses, as well as the Green Line LRT, will run at all hours, Metro Transit spokesman Howie Padilla said Saturday. The Target Field will also stay open all night, and people will be allowed to stay overnight in the ABC ramps: the 4th, 5th and 7th Street garages, and the Leamington and Gateway garages. The Union Depot station in downtown St. Paul is open from 5 a.m. to 2 a.m.

Sunday's high in the Twin Cities metro area will be in the single digits below zero, with windchills as low as minus 30, according to the National Weather Service in Chanhassen. Sunday night's lows will be in the double digits below zero.

Padilla said passengers should join train operators and Metro Transit police in keeping a lookout for signs of anyone exhibiting symptoms of frostbite or other weather-related ailments.

"There's the obvious advice to bundle up, but the other thing I don't think can be reiterated enough is for people to look out for each other," he said.

"We've been a little bit spoiled this year," Padilla said. "But even nice winters have days, weeks and months where we're reminded that we are in Minnesota."