Portlanders who heeded the transportation bureau's winter weather warning for this morning were relieved to wake up to snow-free roads.

According to the National Weather Service of Portland, low-elevation road temperatures yesterday evening were too warm for snow to stick. Tonight, however, the agency warns of the potential for black ice to form.

Jon Bonk, a meteorologist with the NWS, says higher elevations around the Portland foothills did see a small accumulation of snow this morning.

"By and large, most populated metro areas had about an inch or less of overnight snow," Bonk says, "but up in the foothills there were 3-5 inches."

While the city avoided traffic mayhem this morning, Bonk warns that the weather system that brought rain and snow to Portland last night is going to continue. After today's showers, Bonk says "we're going to see breaks in the clouds and temperatures that fall below freezing in time for tomorrow morning's commute."

"Any moisture that's still on the road could freeze over into black ice," Bonk says. "Any road left untreated is going to be fairly slick tomorrow."

Last night, PBOT crews were busy salting and de-icing city roads. On bridges, overpasses and hilly areas, the city uses a liquid magnesium chloride salt brine to lower the temperature that water freezes at. Other priority routes get a coating of road salt.

Dylan Rivera, a spokesman for PBOT, says the agency will continue to treat roads "all day today and throughout tonight."

A map of the streets that the city has treated can be accessed here.